Sessione 1.2

GNGTS 2009

sessione 1.2

Processi tettonici: osservazioni e modelli

Convenor: A. Argnani e I. Marson

GNGTS 2009 SESSIONE 1.2

ADRIA TOP TO BOTTOM: A RECEIVER FUNCTION PERSPECTIVE A. Amato, I. Bianchi, N. Piana Agostinetti Ist. Naz. Geofisica e Vulcanologia, Centro Nazionale Terremoti, Roma

The Adria microplate is a key element in the geodynamic evolution of the Mediterranean. Although there are still different views about its role in the long history of Eurasia-Nubia plate convergence, it is generally accepted that Adria played an important part in the frame of the subduction/collision process of the region. However, a deep knowledge of its internal lithospheric structure is still missing. In this contribution we show some preliminary results of a study of the Adria crust and upper mantle using teleseismic receiver functions. In a recent paper, we analyzed teleseismic receiver functions of 175 broad band seismic stations in Italy and proposed a new Moho map of peninsular Italy (Piana Agostinetti and Amato, 2009, see Fig. 1). Fig. 1 above and the the vertical sections published in the paper by Piana Agostinetti and Amato (2009, see also the references therein) show very well the westward deepening of the Adriatic Moho from the Adriatic coast below the Apennines. This map was obtained considering a homogeneous crust and therefore can be improved to solve details of the crustal structure, useful for geodynamic studies. For instance, it is extremely interesting to understand how much of the Adriatic crust has been dragged down or peeled off during continental subduction, whether this process is continuous along the belt or has some irregularities, the meaning of the seismicity associated to Adria below the belt etc. As a first step in this direction, we start looking at the broad band seismic stations located directly above or very close to the Adria plate. We consider 28 stations of the INGV National Seismic Network from the Apulia southernmost tip to the Po Plain. We compute layered 1-D S-velocity models below each station, using a trans-dimensional RJMCMC (Reversible Jump Markov Chain Monte Carlo) inversion procedure recently developed by Piana Agostinetti and Malinverno (2009). This innovative technique permits to retrieve the Vs model beneath a seismic station without giving a priori constraints on the model parameteri- zation (number and thickness of layers, etc.) as usually done in typical receiver function studies. The results obtained to date are consistent with previous knowledge (deep wells, active seismic profiles, tomographic studies, etc.) with an improved areal coverage and extending to the whole deep crust and upper- most mantle, revealing interesting and original features. In this talk we show some preliminary results on selected Adriatic stations. As an example, we show in Fig. 1 – Moho depth in Italy from teleseismic receiver functions (from Piana Agostinetti and Amato, 2009).

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Fig. 2 – Vs preliminary model obtained from the inversion of teleseismic receiver functions at Minervino Murge (MRVN), in Apulia.

Fig. 2 of the technique applied to the INGV station Minervino Murge (MRVN), located in correspondence of the Puglia-1, 7-km deep well. The Vs profile shows the high Vs, Meso- Cenozoic limestone succession, over a ~3-4 km thick low Vs layer, attributed to the Paleozoic basement. Below this, higher Vs from ~12 to ~18 km depth and a low Vs lower crust from ~18km depth to the Moho, at ~30 km depth. References Piana Agostinetti N., Amato A.; 2009: Moho depth and Vp/Vs ratio in peninsular Italy from teleseismic receiver functions, J. Geophys. Res., 114, B06303, doi:10.1029/2008JB005899. Piana Agostinetti N., Malinverno A., 2009, Receiver function inversion by trans-dimensional Markov chain Monte Carlo sampling, submitted to Geophys. J. Int.

TOMOGRAPHIC IMAGES AND ANALYSIS OF STRESS AND STRAIN TENSORS AT MT. ETNA: THE MAGMATIC UNREST LEADING TO THE 2008 ETNA ERUPTION S. Alparone, G. Barberi, O. Cocina, E. Giampiccolo, C. Musumeci, D. Patanè Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Catania

We analysed the seismic activity pre- ceding and accompanying the onset of the 2008 Mt. Etna eruption. Since January 2008, a clear seismic evidence of a magmatic unrest of the volcano was observed. Seismicity was firstly located in the southwestern sector of the volcano, at depth ranging between 10 and 20 km, along two tectonic structures (NE-SW and NNW-SSE) usually associated with deeper magmatic recharge mechanisms (Figs. 1, 2). Afterwards, the seismicity was located along the shallower portions of the main structures of the northeastern and southern flanks of the volcano (Figs. 1, 2). On May 13, 2008 an intense seismic swarm (about 230 events in 7 hours) announced the beginning of the eruption (Fig. 1, white circles). Fig. 1 - Epicentral map of the analyzed seismicity.

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GNGTS 2009 SESSIONE 1.2

Fig. 2 - Time-Depth distribution of the analyzed seismicity.

In order to provide seismological constraints to the magmatic unrest of the volcano, 336 earthquakes recorded from January 2007 to May 2008 (magnitude greater than 1.0) were selected for stress and strain tensors computation and 3D velocity and attenuation structure determination. This in order to individuate possible stress variations caused by the activation of magmatic sources which can be well evidenced by 3D tomographic images.

SEISMIC IMAGES OF DEFORMATION STRUCTURES OFFSHORE THE EASTERN FLANK OF MOUNT ETNA A. Argnani1, F. Mazzarini2, C. Bonazzi1, M. Bisson2, I. Isola2 1 ISMAR-CNR, Bologna, Italy 2 Istituto Nazionale di Geofisica e Vulcanologia, Pisa, Italy In spite of the clear evidence of active flank dynamics that is affecting the eastern side of Mount Etna, the nature and extent of volcano-tectonic processes have not been fully understood. In order to explain the observed flank deformation different models have been proposed, which are mostly based on onshore structural data. The eastern flank of Mount Etna, however, presents a remarkable topographic step towards the Ionian Sea, with the sea floor reaching a water depth close to 1 km not far from the coastline. Offshore Mount Etna evidence of gravitational instability has been previously reported in the form of submarine landslides (Argnani and Bonazzi, 2005; Pareschi et al., 2006), suggesting that gravitational dynamics affects at least the upper sedimentary succession in this region. The onshore flank deformation of Mount Etna appears to be laterally confined by two tectonic guidelines, trending roughly E-W, located to the north and south of the deforming flank. The northern guideline, in particular, takes the surface expression of a sharp fault (Pernicana Fault). Kinematic models often assume that these boundary structures continue offshore as linear features, connected to a frontal thrust ramp (i.e., Borgia et al., 1992). The occurrence of this offshore structural system, however, has never been documented. This contribution aims at describing the deformation located offshore Mount Etna using multichannel seismic profiles recently acquired during three seismic surveys (Argnani and Bonazzi, 2005; Pareschi et al., 2006; Argnani et al., 2009). These surveys total over 800 km of high resolution seismic profiles, with record length ranging between 3 and 6 seconds and spatial coverage varying from 16 to 48 folds. Seismic profiles show various kinds of gravitational instabilities, operating at different scales, along the offshore extent of Mount Etna. In some instances, a possible control of deep structures on superficial gravitational deformation can also be observed. In general, seismic data show that a remarkable degree of structural complexity occurs offshore Mount Etna (e.g., Fig. 1). It has been observed that the Pernicana Fault is not continuing offshore as a sharp feature; rather, the deformation is expressed in a more complex pattern, already close to the coastline.

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Fig. 1 – Example of seismic profile located offshore Mount Etna showing a complex set of contractional structures. Note fault-related fold with eroded top in the center of the figure.

Preliminary results suggest that tectonic structures might have affected the offshore of Mount Etna before the Pernicana Fault system was developed. However, the nature and significance of these structures and its relationship with the regional tectonic framework (e.g., Argnani, 2009) are still to be fully unravelled. Acknowledgements. This research has been supported by the INGV-DPC project FLANK. The officers and crews, and the participants in the seismic cruises during which the data were acquired are kindly acknowled- ged for their support. References Argnani A.; 2009: Evolution of the southern Tyrrhenian slab tear and active tectonics along the western edge of the Tyrrhenian subducted slab. In: Van Hinsbergen, D. J. J., Edwards, M. A. & Govers, R. (eds) Collision and Collapse at the Africa–Arabia–Eurasia Subduction Zone. The Geological Society, London, Special Publications, 311, 193–212. Argnani A., Bonazzi C.; 2005: Tectonics of Eastern Sicily Offshore. Tectonics, 24, TC4009, doi:10.1029/2004TC001656. Argnani A., Brancolini G., Bonazzi C., Rovere M, Accaino F., Zgur F., Lodolo E.; 2009: The results of the Taormina 2006 seismic survey: Possible implications for active tectonics in the Messina Straits. Tectonophysics, in press. Borgia A., Ferrari L., Pasquare’ G.; 1992: Importance of gravitational spreading in the tectonic and volcanic evolution of Mount Etna, Nature 357, 231-235. Pareschi, M. T., E. Boschi, F. Mazzarini, Favalli M.; 2006: Large submarine landslides offshore Mt. Etna, Geophys. Res. Lett., 33, L13302, doi:10.1029/2006GL026064.

VARIAZIONE SPAZIO-TEMPORALE DELLA DEFORMAZIONE SISMICA NELL’AREA DELL’AQUILANO S. Barani, C. Eva Dipartimento per lo studio del Territorio e delle sue Risorse, Università degli Studi di Genova

Il calcolo del tasso di deformazione sismica (seismic strain rate) in aree sismicamente attive è argomento di studio da oltre un cinquantennio. Se i primi studi si basano sul calcolo del flusso tettonico (tectonic flux) (es. St. Amand, 1956; Cattaneo et al., 1981), una misura dell’energia rilasciata dai terremoti in una data area in un dato intervallo di tempo, quelli più recenti calcolano lo strain rate in funzione del tasso di momento sismico (seismic moment rate) (es. Anderson, 1986; Rao, 2000; Mazzotti and Hyndman, 2002; Mazzotti and Adams, 2005; Hyndman et al., 2005), da dati

142 GNGTS 2009 SESSIONE 1.2 geologici (e.g., Wesnousky et al., 1982) o tramite misure geodetiche (es. Serpelloni et al., 2005; D’Agostino et al., 2008). Scopo del presente studio è l’analisi dell’evoluzione spazio-temporale della deformazione sismica nell’area colpita dal terremoto dell’Aquila del 6 aprile 2009 (Mw = 6.3) a partire da un catalogo di terremoti rappresentativo non solo della sismicità strumentale dell’area ma anche della sismicità storica. A tal scopo è impiegato il metodo proposto da Barani et al. (2009), metodo che implementa un approccio a sismicità diffusa (spatially smoothed seismicity approach) per il calcolo del tasso di momento sismico, simile a quello proposto da Frankel (1995) per la valutazione della pericolosità sismica degli Stati Uniti centro-orientali. Rispetto all’approccio originale di Frankel (1995), che sfrutta una funzione di smoothing di tipo circolare, i tassi di momento sono calcolati applicando un kernel gaussiano di tipo ellittico (smoothing bidimensionale) al fine di considerare l’orientazione. preferenziale delle faglie sismogenetiche. presenti nell’area di studio. Noto il moment rate, M0, il tasso di deformazione sismica, ε , è calcolato secondo il metodo di Anderson (1979):

dove k è un coefficiente regionale che dipende dal campo di stress, ovvero dal meccanismo di 2 fagliazione prevalente, µ = 3.6 · 1010N/m è il modulo di taglio, A è l’area della sorgente sismica. (ovvero, dato l’approccio a sismicità diffusa, di una cella del grid impiegato per il calcolo di M0) e h è lo spessore sismogenetico. Tra i parametri in gioco, il moment rate è quello più critico (e.g., Anderson, 1986; Field et al., 1999; Mazzotti and Adams, 2005) in quanto il momento sismico dei terremoti, M0, da cui esso deriva, molto spesso segue dall’applicazione di equazioni di conversione tra scale di magnitudo differenti e, pertanto, risulta affetto da un’incertezza significativa. Al fine di considerare tale incertezza e quella nei valori di h è impiegato un approccio di tipo Monte Carlo, consistente nel variare in modo casuale (random) i valori di Mw e h nota una stima dell’errore ad

Fig. 1 – Distribuzione del tasso di deformazione prima e dopo la sequenza sismica a seguito del terremoto del 6 Aprile.

143 GNGTS 2009 SESSIONE 1.2 assi associato. Nota la completezza del catalogo sismico, sono prodotte mappe rappresentati la distribuzione geografica di per diversi intervalli temporali. Da queste è possibile studiare l’evoluzione nello spazio e nel tempo della deformazione sismica ed individuare gap di sismicità lungo allineamenti/sistemi di faglie presenti nell’area di studio. In Fig. 1 è mostrata. la distribuzione del tasso di deformazione prima e dopo l’evento del 6 aprile. I massimi valori di ε (≈ 50 10-9 yr-1), orientati in direzione appenninica, sono concentrati in corrispondenza delle faglie “Ovindoli-Pezza” e “Fucino-Basin” (Basili et al., 2008). A quest’ultima è associato il terremoto distruttivo di Avezzano del 1915 (Mw = 7.0). Dal confronto tra le mappe in Fig. 1 è evidente un gap deformativo in corrispondenza della faglia di Montereale (“Montereale Basin”), successivamente colmato a seguito del terremoto del 6 aprile e successivi. Si nota, infatti, un incremento dello strain rate da circa 30 10-9 yr-1 a 38-40 10-9 yr-1. I valori di così calcolati saranno confrontati con quelli ottenuti da misure geodetiche qualora disponibili. Tale confronto risulta fondamentale per la caratterizzazione di modelli sismogenetici funzionali al calcolo della pericolosità sismica dell’area, ovvero per una stima corretta dei tassi di ricorrenza associati a forti terremoti. Talvolta, infatti, discrepanze tra tassi deformativi da dati sismici e geodetici (e/o geologici) sono indice, oltre che dell’esistenza di processi asismici attivi, di incompletezza del record (catalogo) sismico per quanto concerne i massimi terremoti associabili all’area di studio. Bibliografia Anderson J. C.; 1986: Seismic strain rates in the Central and Eastern United States. Bull. Seism. Soc. Am., 76, 273-290. Anderson J. G.; 1979: Estimate the seismicity from geological structure for seismic-risk studies. Bull. Seism. Soc. Am., 69, 135- 158. Barani S., Scafidi D. and Eva C.; 2009: strain rates in northwestern italy from spatially smoothed seismicity. Submitted to J. Geophys. Res. Basili R., Valensise G., Vannoli P., Burrato P., Fracassi U., Mariano S., Tiberti M. M. and Boschi E.; 2008: The Database of Individual Seismogenic Sources (DISS), version 3: summarizing 20 years of research on Italy’s earthquake geology. Tectonophysics, 453, 20-43. Cattaneo M., Eva C. and Merlanti F.; 1981: Seismicity of Northern Italy: a statistical approach. Bollettino di Geofisica Teorica e Applicata, 89, 31-42 D’Agostino N., Mantenuto S., D’Anastasio E., Avallone A., Barchi M., Collettini C., Radicioni F., Stoppini A. and Castellini G.; 2008: Contemporary crustal extension in the Umbria-Marche Apennines from regional CGPS networks and comparison between geodetic and seismic deformation. Tectonophysics, doi:10.1016/j.tecto.2008.09.033. Field E. H., Jackson D. D. and Dolan J. F.; 1999: A mutually consistent seismic-hazard source model for Southern California. Bull. Seism. Soc. Am., 89, 559-578. Frankel A.; 1995: Mapping seismic hazard in the Central and Eastern United States. Seism. Res. Lett., 66, 8-2. Hyndman R. D., Flük P., Mazzotti S., Lewis T. J., Ristau J. and Leonard L.; 2005: Current tectonics of the northern Canadian Cordillera. Can. J. Earth Sci., 42, 1117-1136. Mazzotti S. and Adams J.; 2005: Rates and uncertainties on seismic moment and deformation in eastern Canada. J. Geophys. Res., 110, 1-16. Mazzotti S. and Hyndman R. D.; 2002: Yakutat collision and strain transfer across the northern Canadian Cordillera. Geology, 30, 495-498. Rao B. R.; 2000: Historical seismicity and deformation rates in the Indian Peninsular Shield. J. Seism., 4, 247-258. Serpelloni E., Anzidei M., Baldi P., Casula G. and Galvani A.; 2005: Crustal velocity and strain-rates fields in Italy and surrounding regions: new results from the analysis of permanent and non-permanent GPS networks. Geophys. J. Int., 161, 861-880. St. Amand P.; 1956: Two proposed measures of seismicity. Bull. Seism. Soc. Am., 46, 41-45. Wesnousky S. G., Scholz C. H. and Shimazaki K.; 1982; Deformation of an island arc: rates of moment release and crustal shortening in intraplate Japan determined from seismicity and Quaternary fault data. J. Geophys. Res., 87, 6829-6852.

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PRELIMINARY RESULTS ON THE INVESTIGATION OF SEISMOGENIC FAULTS IN ITALY THROUGH ANALOGUE MODELING: FROM THE MESSINA STRAITS TO THE ABRUZZO REGION L. Bonini 1, D. Di Bucci 2, S. Seno 1, G. Toscani 1, G. Valensise 3 1 Dipartimento di Scienze della Terra, Università di Pavia, Italy 2 Dipartimento della Protezione Civile, Rome, Italy 3 Istituto Nazionale di Geofisica e Vulcanologia, Rome, Italy

A simple normal fault plane can be schematically depicted by an elliptical surface with the major axis usually subhorizontal (Marchal et al. 2003 and references therein), but this configuration can change if the fault interacts with other faults producing complex geometries and discontinuous map traces. Through the years, several studies focused on the fault growth in two and three dimensions with different approaches (among many others: Keven and Martel, 2007 and references therein). The characterization of seismogenic faults in tectonically active regions begins from an accurate definition of their geometry and kinematics. In Italy this characterization is quite complex, because many large seismogenic faults are not clearly and unambiguosly expressed at the surface (see Valensise and Pantosti, 2001, for a review), whereas in other regions with higher deformation rates a clear geological evidence is often associated with large earthquakes (e.g. Liu-Zeng et al. 2009). Therefore, the characterization of the Italian seismogenic faults and of their mutual interactions it is not always straightforward; in this case, analogue modeling can provide an independent and useful tool for the interpretation of the surface geological data. Analogue modeling applied to earthquake geology is a quite innovative technique: when combined with other datasets (e.g.: seismic tomography, seismic profiles, well-logging data, field geology, morphotectonic and paleoseismo- logical data) it can provide significant insights on the long term (i.e. Quaternary) evolution of a seismogenic fault. We present two areas characterized by an extensional tectonic regime and where major earthquakes are due to the activity of normal fault systems. We first tested our approach on the source of the catastrophic 28t December 1908 Calabro-Messinese earthquake (Mw 7.1; CPTI Working Group, 2004), one of the largest seismogenic faults in the central Mediterranean Sea. The geometry of this fault is the object of a lively debate. Among the many models available, those which encompass geological data can be grouped in two families: the first one interprets the seismogenic fault as a buried, SE dipping, low angle normal fault, compatible with, the magnitude, coseismic effects and damage patterns of the 1908 earthquake and with the Upper Pleistocene morphotectonic evolution of the epicentral area). On the contrary, the second family presents a seismogenic fault model formed by a ca. NW-dipping, high-angle normal fault associated with one of the Quaternary faults identified on-shore and off-shore. However, the geometry and the limited displacement of these faults do not compare well with the 1908 magnitude, coseismic effects and damage pattern.

Fig. 1 - A) 3D schematic representation of the undeformed experimental apparatus designed for the Messina Straits experiments. B) Example of a vertical section of the Messina Straits experiment after fault activation (extension: 2 cm).

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The analogue models that have been carried out so far (Fig. 1) suggest that surface faulting is not self-governing but can be explained as a direct consequence of the long-term activity of the deeper and buried low-angle seismogenic fault (Bonini et al., 2009), thus allowing all available geological data to be reconciled in a structurally coherent fault model. The second case study is represented by the Abruzzo region: in particular, our purpose was to investigate the long term interaction between the seismogenic fault responsible for the 6 April 2009, L’Aquila earthquake (Mw 6.3) and an adjacent seismogenic fault located to the ESE of the seismic sequence that followed the L’Aquila main shock. Ongoing studies (Di Bucci and Valensise, 2009) have shown that the Barisciano-Civitaretenga basin is underlain by a major active fault similar to the L’Aquila fault, which suggests an equivalent earthquake potential (Mw 6.2-6.4). We adopted the same analogue modeling approach used for the Messina Straits for a threefold goal: 1. testing our modelling approach on a well constrained seismogenic source; 2. investigating the relationships between the surface geology and the deeper seismogenic faults; 3. investigating the structural relationship in the transfer zone between these two seismogenic faults. We carried out a set of analogue models at 1:100,000 scale that reproduce in 3D two normal faults with a relatively low dip angle (45-50°; Fig. 2).

Fig. 2 - Experimental setup of the Abruzzo test in a configuration with the two faults used to generate extension in overlying granular materials.

In the first set we tested the simultaneous activation of the two master faults, whereas in the second we checked an alternating displacement on the fault planes. Preliminary results have showed the mutual control between the two structures, both in the distribution of displacement on the fault planes and on the development of the overlying associated basins. References Bonini L., Di Bucci D., Seno S., Toscani G., Valensise G.; 2009. Reconciling large seismogenic and shallow normal faults in the Messina Straits: the analogue modeling perspective. Geophysical Research Abstracts, Vol. 11, EGU2009-12425. Di Bucci D., Valensise G.; 2009. Surface faults, seismogenic source and their morphotectonic signature: lesson from the 6 April 2009 l’Aquila earthquake and implication to adjacent seismogenic areas (Middle Aterno). Epitome Geoitalia 2009. 3, pp. 173. Marchal D., Guiraud M., Rives T.; 2003. Geometric and morphologic evolution of normal fault planes and traces from 2D to 4D data. Journal of Structural Geology, 25, 135-158. Keven J. O., Martel S. J.; 2007. Growth of surface-breaching normal faults as a tree-dimensional fracturing process. Journal of Structural Geology, 29, 1463-1476.

146 GNGTS 2009 SESSIONE 1.2

ASSETTO TETTONICO E SISMICITÀ NELL’APPENNINO CENTRALE F. Calamita, A. Pizzi, V. Scisciani, S. Satolli, G. Pomposo Dipartimento di Scienze della Terra – Università degli Studi “G. d’Annunzio” Chieti-Pescara

In questo lavoro viene proposto un modello cinematico e sismotettonico per l’Appennino centrale ricostruito sulla base dell’assetto tettonico e della sismicità dell’area. Nell’Appennino centrale le pieghe e i sovrascorrimenti a direzione NW-SE si raccordano a due accavallamenti regionali ad andamento circa N-S (sovrascorrimento Olevano-Antrodoco e Sangro-Volturno) e nell’insieme descrivono due principali fronti a geometria arcuata. Inoltre, nell’Appennino umbro-marchigiano faglie transpressive destre orientate N-S definiscono ulteriori motivi arcuati più interni e concentri- ci a quelli principali suddetti. Il controllo da parte di faglie normali pre-orogeniche sulla geometria arcuata delle strutture della catena è ben ricostruibile dalla geologia di superficie, di sottosuolo e tramite l’interpretazione di profili sismici. Calamita et al., (2009) ricostruiscono un modello di tettonica d’inversione che prevede la completa riutilizzazione delle faglie normali pre-thrusting ad andamento N-S come sovrascorrimenti durante il Neogene (come ad esempio la linea Ancona- Anzio Auctt. nel sovrascorrimento Olevano-Antrodoco). Invece, le faglie pre-esistenti orientate NW-SE sono dislocate dai sovrascorrimenti che seguono una traiettoria di tipo shortcut all’interno della crosta superiore. Pertanto, le faglie normali pre-esistenti, trasportate passivamente nel blocco di tetto dei sovrascorrimenti crostali, si rinvengono nei fianchi occidentali delle pieghe ad andamen- to NW-SE e terminano in corrispondenza dei tratti N-S delle strutture della catena. Le faglie normali presenti nella dorsale appenninica umbro-marchigiano-abruzzese presentano chiare evidenze di attività tardo-quaternaria e sono responsabili dell’intensa attività sismica. Pertanto le faglie normali ad andamento NW-SE, precedentemente dislocate dai sovrascorrimenti neogenici con geometria shortcut, sono state riattivate a partire dal Pleistocene a seguito della tettonica estensionale che sta interessando la dorsale appenninica umbro-marchigiano-abruzzese e risultano compartimentalizzate dai motivi transpressivi ad alto angolo e dai sovrascorrimenti orientati N-S (Pizzi & Galadini 2009). La spaziatura di tali strutture N-S e lo spessore fragile della crosta controllano la segmentazione e la crescita longitudinale delle faglie, le profondità ipocentrali e l’energia rilasciata durante le sequenze sismiche che avvengono nei vari settori (dorsale appenninica umbro-marchigiana, Monti della Laga e dorsale appenninica laziale-abruzzese), rispettivamente delimitati da motivi transpressivi ad alto angolo e sovrascorrimenti crostali con entità di raccorciamento di qualche chilometro ad andamento N-S ed E-W (faglia della Valnerina, sovrascorrimento Olevano-Antrodoco, sovrascorrimento del Gran Sasso e sovrascorrimento Sangro-Volturno). La tettonica attiva dell’arco dell’Appennino centro-settentrionale comprende un fronte compres- sivo rappresentato dalle strutture sepolte della Pianura Padana e dell’off-shore adriatico (Porto S. Giorgio-Promontorio del Conero), raccordate a sud alla rampa obliqua Sangro-Volturno, e faglie normali nella dorsale umbro-marchigiano-abruzzese, localizzate nel blocco di tetto di tale arco. In tale contesto, è possibile ricostruire (in accordo con Boccaletti et alii, 2005, e Viti et alii, 2009) un modello dinamico per l’Appennino centro-settentrionale che prevede una sollecitazione con andamento NNW-SSE parallela alle strutture della catena connessa con la cinematica delle placche, responsabile dell’estrusione laterale di archi crostali/litosferici con estensione nei settori interni, compressione al fronte e zone di deformazione trascorrente ed obliqua lungo faglie ad andamento circa N-S ed E-W nel settore interposto e nell’antistante area di avampaese. Bibliografia Boccaletti M., Calamita F., Viandante M.G.; 2005: La Neo-Catena litosferica appenninica nata a partire dal Pliocene inferiore come espressione della convergenza Africa-Europa. Boll. Soc. Geol. It, 124, 87-105. Calamita F., Esestime P., Paltrinieri W., Scisciani V., Tavarnelli E.; 2009: Structural inheritance of pre- and syn-orogenic normal faults on the arcuate geometry of Pliocene-Quaternary thrusts: Examples from the Central and Southern Apennine Chain. Ital.J.Geosci. (Boll.Soc.Geol.It.), 128, No. 2, 381-394. Pizzi, A., Galadini; 2009: Pre-existing cross-structures and active fault segmentation in the northern-central Apennines (Italy). Tectonophysics , doi:10.1016/j.tecto.2009.03.018. Viti M., Mantovani E., Babbucci D., Tamburelli C.; 2009: Generation of Trench-Arc-Back Arc Systemsin The Western Mediterranean Region driven by plate convergence. Ital.J.Geosci. (Boll.Soc.Geol.It.), 128, No. 1, 89-106.

147 GNGTS 2009 SESSIONE 1.2

DETECTION OF SURFACE MOVEMENTS DURING THE ABRUZZO 2009 EARTHQUAKE BY GNSS TECHNIQUES A. Caporali Department of Geosciences, University of Padova

The April 6, 2009, Mw=6.3 earthquake in Abruzzo (Central Italy) is associated with displacements on the surface which are well visible in the time series of permanent GPS stations within few tens of km from the epicentre. By combining the observed coseismic 3D displacements with an elastic dislocation model we obtain estimates for the position and orientation of the fault plane, and the slip vector at depth. The results are compared with similar results obtained by GPS, but a par- tially different set of stations, InSAR with Envisat and Cosmos SkyMed data, and classical seismological techniques of hypocenter location and fault plane solution, finding in most cases an excellent agreement. The analysis of the GPS time series has additional information not yet exploited: several signals are visible in the time series but are not associated with seismic events. We investigate a number of these features at high time resolution (30 s) using the kinematic mode of the Bernese software. Thus the Abruzzo earthquake offers an interesting example of how space borne techniques (InSAR, GNSS) can monitor creep and transient deformation leading to and following brittle failure, complementing the data obtained by classical seismological techniques.

PRESENT DAY HORIZONTAL VELOCITIES OF PERMANENT GPS STATIONS AND THE IMPLIED REGIONAL STRAIN RATE FIELD A. Caporali Dipartimento di Geoscienze, Università di Padova

We present a set of horizontal velocities in the Italian and surrounding areas computed by stacking normal equations of weekly network adjustments of permanent GPS stations starting 1999 and extending to September 2009. The individual normal equations have removable constraints, and the stacking is accomplished by imposing one set of constraints in position and velocity, according to the ITR2005 realization of the ITRS. Velocities computed out of an Eulerian, rigid body model of the Eurasian plate rotation are subtracted from the resulting velocities, and a picture of the implied kinematics is obtained in a rigorous way. The greatest increase in detail is obtained in NE Italy, where the inclusion of GNSS stations of the Province of Bolzano, the Veneto and Friuli VG regions enable the kinematics of the surface deformation to be detailed with unprecedented resolution. Considerable more information is obtained in Central Southern Italy, where several stations from RING of INGV and networks of Regional Governments again contribute to improve the resolution. To better constrain the boundaries of the national territory, we further present the combination of our network with a Central European Network CEGRN recently computed with identical approach and standards within the TopoEurope project, which has several stations in Austria and former Yugoslavia. The strain rate is computed with reference to this larger network. The evaluation is done at the center of the ZS9 seismic zones of INGV, with the intent to providing for each ZS an estimate of the zonal deformation taking place at present. Comparison of the strain rate eigenvectors with fault plane solutions PT axes projected to the horizontal give a quantitative estimate of the relation between the principal directions of seismic stress release and the principal directions of ground deformation.

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NEOGENE-QUATERNARY TECTONIC STRATIGRAPHY OF THE EASTERN SOUTHERN ALPS, NE ITALY R. Caputo1, M.E. Poli2, A. Zanferrari2 1 Department of Earth Sciences, University of Ferrara 2 Department of Georesources and Territory, University of Udine

Based on the fact that the available chronology and stratigraphy of the Neogene-Quaternary sedimentary succession within the Eastern Southern Alps is very detailed (Zanferrari et al., 2008; and references therein), we investigated the external sector of the Eastern Southern Alps and performed a detailed structural and stratigraphic mapping of the Tortonian-Quaternary sedimentary units outcropping within a 120 km-long zone along the foothills of the mountain chain in Veneto and Friuli regions (Fig. 1). The Eastern Southern Alps is a major strucural subdivision of the broader Alpine Chain and it is conventionally delimited to the north by the Periadriatic Lineament. From a tectonic point of view, the Eastern Southern Alps correspond to a distinct late Oligocene-Quaternary oro- gene (Castellarin et al., 2006). This south-verging fold-and-thrust belt was generated during the complex crustal collision and indentation of the Adria promontory underneath the Alpine chain. Due to the relatively large distribution of conglomeratic bodies within the considered stratigraphic interval, we focused our attention on numerous deformed pebbles characterised by pitted surfaces. These structural features are classically related to small-scale pressure-solution processes mainly occurring along those particle contacts that are roughly oriented perpendicular to the direction of maximum compression. Based on the careful analysis of the shape and orientation of the indented features on the pebbles’ surface and following a statistical approach based on as many as possible measurements for each site, the mean orientation of the maximum compressive stress axis (σ1) is obtained by contouring the data on a stereonet and calculating the density peak. We focus on

Fig. 1: Geological map of the investigated area (dashed line). 1: pre-Tortonian successions; 2: Tortonian-Messinian sedimentary units; 3: Pliocene-Pleistocene sedimentary units. Dots represent the sites of meso-structural investigations. TB = Thiene-Bassano Thrust, BC = Bassano-Cornuda Thrust, MC = Montello Thrust, CA = Cansiglio Thrust, PM = Polcenigo-Maniago Thrust, AR: Arba-Ragogna Thrust, ST: Susans-Tricesimo Thrust.

149 GNGTS 2009 SESSIONE 1.2 the Tortonian-Quaternary deposits outcropping along the foothill belt facing the Veneto-Friuli plain between the Brenta River, to the west, and the Tagliamento River, to the east (Fig. 1). As a whole, the investigated stratigraphic units show a typically clastic shallowing upwards sequence represent- ing the infilling of the Eastern Southalpine foredeep-foreland basins, which developed from Late Oligocene to Pleistocene (Massari et al., 1986; Fantoni et al., 2002). The investigated stratigraphic succession can be separated into three principal units. 1) Tortonian to lower Messinian conglomerates. These deposits correspond to the upper part of the Vittorio Veneto Sandstone (VVE) and to the Montello Conglomerate (MON). They largely crop out along the whole study area. 2) Lower Pliocene conglomerates. They correspond to the Osoppo Conglomerate (OSP) exclusively cropping out in the easternmost sector of the investigated area. 3) Late Pliocene - Early (to Middle?) Pleistocene conglomerates of the Coneglaino Unit (CON) that includes the pelitic-conglomeratic layers of the Conegliano, Refrontolo and Caneva area. These continental clastic deposits overlie the marine Pliocene sediments of Cornuda (COR). Tectonic stratigraphy. Using the above methodological approach, the occurrence of four distinct deformational events has been determined (Fig. 2). 1) Late Tortonian event. Five localities belonging to the Montello Conglomerate and par- ticularly to its lower and middle members or to the Vittorio Veneto Sandstone represent a first group of sites showing a cluster of mean compressional axes, which are all parallel to the strongly dipping

Fig. 2: Synthetic diagram showing the Tortonian p.p.-Pleistocene sedimentary stratigraphy (units), the period of activity for the major tectonic structures (thrusts), the direction of maximum compression estimated from the meso- structural analyses (?1), the tectonic stratigraphy of the Eastern Southern Alps with the principal deformational events (dark sectors) and the corresponding table including all datasets (event), the direction of relative motion of Africa with respect to Europe (AFR/EUR; numbers refer to normal magnetic anomalies, while arrows thickness is proportional to the amount of relative convergence; Mazzoli and Helman, 1994).

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layers. Following the palinspastic restorations the pre-tilting sub-horizontal σ1 axes trend NW-SE with an average orientation of 313°/00°. The lower chronological constraint for this deformational event is provided by the age of the youngest affected deposits (i.e. late Tortonian), while the imprinting process certainly occurred before the beginning of the large-scale fault-propagation- folding, and the consequent tilting, associated with the Bassano-Valdobbiadene and Cansiglio- Maniago thrusts, whose paroxistic activity started in early Messinian (Castellarin et al., 2006). 2) Late Messinian-Early Pliocene event. Eleven sites belonging to the Vittorio Veneto Sandstone and both lower and upper members of the Montello Conglomerate represent a second group of measurements. In most sites the observed compressional features are parallel to layering or form a low intersecting angle. The palinspastic restoration provides a NNW-SSE trending compression with an average orientation of 338°/04°. As concern the timing, this is constrained i) by the age of the youngest affected rocks (early Messinian) and ii) by the full development of the Bassano- Valdobbiadene and Cansiglio-Maniago thrusts, as lower and upper chronological boundaries, respectively. 3) Late Pliocene event. Seven sites have been included in this group, which is again characterised by a mean NW-SE direction of compression (314°/03°). This value is similar and statistically equivalent to that of the Late Tortonian event but there are two main reasons for separating the two datasets and inferring a distinct deformational event. Firstly, in four out of seven sites the youngest affected conglomerates belong to the Early Pliocene Osoppo Conglomerate or even to the Late Pliocene-Early Pleistocene Unit, therefore constraining the lower chronological boundary. Secondly, in the three remaining sites affecting the older Montello Conglomerate the layering is steeply dipping while the measured meso-scale contractional features are horizontal. This observation suggests that they have been imprinted after the occurrence of the macro-scale tilting process associated with the fault-propagation folding of the Bassano-Valdobbiadene and Cansiglio-Maniago thrusts (Messinian to Early Pliocene in age accordingly to Castellarin et al., 1992). Thus confirming the timing of this deformational event: Late Pliocene at the oldest. 4) Early-Middle Pleistocene event. The largest dataset obtained from the investigated area con- sists of seventeen sites forming a last group of mesostructural measurements. They are characterised by a renewed NNW-SSE-trending direction of compression with an average orientation of 160°/03°. Notwithstanding a perfectly matching mean σ1 direction with that of the Messinian event (338°/04°), the striking difference among the two deformational events and groups of data is due to the fact that the measured compressional directions are all horizontal to sub-horizontal, therefore lacking any significant post-deformation tilting. In conclusion, we can say that this last dataset represents a distinct younger deformational event, which likely started in Early Pleistocene. Taking into account the elapsed time, say 1-1.5 Ma, and comparing the average compressional direction obtained from the meso-structural analyses with that inferred from the seismicity of the area (Bressan et al., 2003), it is likely that this tectonic regime is still active. Discussion. Our reconstruction of the late Tortonian-Quaternary Tectonic Stratigraphy in the Eastern Southern Alps has emphasized the occurrence of four distinct deformational events. It is noteworthy that these events do not represent 'simple' local variations of the stress field because for all datasets the corresponding sites of measurements are spread along the entire 120 km-long investigated area and in many cases, the same localities and sedimentary units are affected by more than one dataset (viz. stress field). In particular, the four events could be recognized and distinguished based on i) a different mean direction of compression and ii) their timing of activity. Accordingly during Late Neogene-Quaternary the stress trajectories of the Eastern Southern Alps were affected by repeated rotations with rapid flipping of the principal horizontal stresses. We refer to this behaviour as Twist Tectonics. The tectonic evolution of the Eastern Southern Alps has been compared with Neogene-Quaternary the convergence direction between Adria-Africa and Europe plates (Fig. 2) showing a good fitting with both timing and directions of compression of the major deformational events. However, since late Messinian, the Northern Apennines were close enough to the Eastern

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Southern Alps in order to perturb the stress field and generate short-lived (1-2 Ma) rotations of the stress trajectories (Twist Tectonics) possibly due to accomodation processes of the Adria indenter and overlapping effects of the two 'remote' engines (Africa and Apennines). References Bressan G., Bragato L. and Venturini C. (2003): Bull. Seism. Soc. Am., 93, 1280-97. Castellarin A., Vai G.B. and Cantelli L. (2006): Tectonophys., 414, 203-223. Fantoni R., Catellani D., Merlini S., Rogledi S. and Venturini S. (2002): Mem. Soc. Geol. It., 57, 301-313. Massari F., Grandesso P., Stefani C. and Zanferrari A.(1986a): Giornale di Geologia, 48(1-2), 235-255, Bologna. Mazzoli S. and Helman M. (1994): Geol. Rund., 83, 464-468. Zanferrari, A., Avigliano, R, Grandesso P., Monegato, G., Paiero G., Poli M.E., Stefani, C. (2008): Note illustrative della Carta geologica d’Italia alla scala 1:50,000 – Foglio 065 “Maniago”; 224 pp. Graphic Linea, Tavagnacco (UD).

THE LATE QUATERNARY CRUSTAL DEFORMATION OF NE SICILY: EVIDENCE FOR AN ACTIVE MANTLE DIAPIRISM S. Catalano, G. Romagnoli, G. Tortorici Dipartimento di Scienze Geologiche, Università di Catania

The origin and the nature of the deformation processes, affecting the volcanic regions of eastern Sicily, are still debated. These regions are, in fact, characterised by the coexistence of both extensional and compressional dynamics that have been evidenced by geological, seismological and geodetic data. A dynamic and kinematic model of the Late Quaternary deformation of the NE Sicily, based on new structural and morphological data, is here discussed in order to provide new tectonic constraints for interpreting the volcanism and the seismicity of the region.

Fig. 1 – Late Quater- nary tectonics of NE-Sicily. The geodetic data are from Hollestein et al. (2003). Uplift-rate measurements are from Catalano & Di Stefano (1997) and Catalano & De Gui- di (2003). Focal mechanisms are from Cello et al. (1982) and Giammanco et al. (2008).

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The investigated area represents a mobile crustal block that, according to the available GPS data, diverges towards the NE, from the rest of the Sicilian collision zone (see inset of Fig. 1). In addition, this crustal block, since 600 ka B.P., has experienced a 1.1 mm/a tectonic uplifting that, higher than in the adjacent Mt. Nebrodi region (<0.8 mm/a) (Fig. 1), produced the displacement of 600 ka-old marine deposits at elevation of about 580 m a.s.l.. The southwestern boundary of the NE Sicily mobile block is to locate along a N100 oriented tectonic alignment, here designed as Naso- Rocca Novara Line (NRL), that extends from Naso to Novara di Sicilia (Fig. 1). This belt is composed of distinct segments of pre-existing discontinuities that have reactivated during the Late Quaternary, to accommodate a vertical displacement of about 200 m. This value corresponds to the entire differential uplift (0,3 mm/a) which has been cumulated in the last 600 ka, between the NE Sicily and the Mt. Nebrodi region. The NE Sicily mobile block is composed of two distinct sectors which are separated by a major NNW-SSE shear zone, here designed as Eolian-Peloritani Shear Zone (EPSZ), which is composed of N-S and N130 oriented fault segments that extend from the Eolian Islands to the Peloritani Mts. (Fig. 1). To the west of the EPSZ, a wide uplifted region is bordered by a flight of Late Quaternary (< 580 ka) marine terraces that crosses almost undisturbed all the major on-shore fault zones. To the east, the EPSZ borders a Late Quaternary (<600 ka) collapsed basin, which is confined to the southeast by the N20-40 oriented, northwestern facing normal faults that control the Peloritani Ridge. The Peloritani faults have cumulated vertical displacements for discrete periods of the Late Quaternary, during which an active abrasion surface developed on their stable hangingwall, while the footwall was uplifting at the rate of the regional signal. The occurrence of three distinct polycyclic terraced abrasion surfaces (OIS 11; OIS 9 and OIS 5), each displaced at averaged uplift-rate of 1.1 mm/a and bordered by fault-controlled sea-cliffs along both their inner- and outer-edges, suggest the progressive migration of the active fault zone towards the NW. The distribution and the geometry of the marine terraces, along the faulted belt, evidence that the Late Quaternary fault motion has exactly balanced the regional uplifting, being concentrated on distinct short-lived coast-bounding fault zones. This long-term behavior strongly suggests a gravity-induced origin for the Late Quaternary fault motions along the southeastern margin of the collapsed basin. The reconstructed mechanism also implies that the active bounding-fault is to be confined in the off-shore of the terraced regions, while the relict branches of the margin, as well as the deactivated portions of the EPSZ, are uplifted in the on-shore. The kinematics on both the (post-

Fig. 2 – Kinematic model of the NE Sicily mobile crustal block. In the sketch map on the left the main active and recent (dashed lines) tectonics are represented. The map also shows the subsiding (-) and the uplifting (+) areas. The profile on the right refers to a section located to the north of the major EPSZ.

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220ka) segments of the EPSZ (stereoplot a in Fig. 1) and the N20 oriented (pre-125 ka) fault segments of the Peloritani margin (stereoplot b in Fig. 1) indicate that fault planes have been activated by both a NW-oriented and a NE-oriented direction of extension. In addition, along the EPSZ, fault planes also display kinematics which are related to a NE-oriented compression. The contribution of three different stress field on remobilizing the active structures is also evidenced by the available seismological data. The main recorded event (e.g. 1978; Cello et al., 1982) is to relate to dextral motion along the off-shore active segments of the EPSZ. The coexistence of the two active direction of extension is demonstrated by focal mechanisms related to the low-magnitude events, which are spread over all the Peloritani margin, to the east of the EPSZ (Giammanco et al., 2008). Lesser events, connected to the NE-SW oriented extension, have been also located to the west of the transfer zone. Finally, the occurrence of NE-SW compression is evidenced by the seismogenic stress field in the area of the Eolian Islands (Neri et al., 2005). The complex kinematic picture of the crustal deformation of NE Sicily (see sketch map in Fig. 2) could represent the shallow expression of a Mantle upwelling at depth. The NE-ward shifting and the differential tectonic uplifting of the entire region, associated with the negative tectonic inversion along the NRL and with the diffuse processes of crustal extension and contraction along the same direction, are consistent with a NE-SW oriented, NE-verging intrusion of a Mantle diapir, beneath the NE Sicily mobile crustal block. As well, the occurrence, between the Eolian Islands and the Peloritani Mountains, of the Late Quaternary basin controlled by the NW-SE extension (see the cross section in Fig. 2), could be related to crustal collapses, accompanying the SE-ward lateral spreading of the Mantle dome at depth. This kinematic model also predicts that major crustal contractional structures, to be fully investigated, have to mark the leading edge of the upwelling mantle body, both in the direction of the main intrusion and, at right angle, in the direction of the lateral spreading. The proposed tectonic picture could represent a new key for interpreting the kinematics and the dynamics governing the seismogenic stress field and the surface deformation in the Eolian area as well as in the Mt. Etna region. References Catalano, S., De Guidi, G., 2003: Late Quaternary uplift of northeastern Sicily: relation with the active normal faulting deformation. Journal of Geodynamic, 36, 445-467. Catalano S., Di Stefano, A.; 1997. Sollevamento e tettogenesi Pleistocenica lungo il margine tirrenico dei Monti Peloritani: integrazione dei dati geomorfologici, strutturali e biostratigrafici. Il Quaternario, 10, 337-342. Cello G., Guerra I., Tortorici L., Turco E., Scarpa R.; 1982: Geometry of the neotectonics stress field in southern Italy: geological and seismological evidence. J. Struct. Geol., 4, 385-393. Hollestein Ch., Kahle H.-G., Geiger A., Jenny S., Geos S. e Giardini D.; 2003: New GPS constraints on the Africa-Europe plate boundary zone in southern Italy. Geophysical Research Letters, 30, NO.18, 1935. Giammanco S., Palano M., Scaltrito A., Scarfì L., Sortino F.; 2008: Possible role of fluid overpressurein the generation of the earthquakes swarms in active tectonic areas, the case of the Peloritani Mountains (Sicily). Journal of Volcanology and Geothermal Research, 178, 795-806. Neri G., Barberi G., Oliva G., Orecchio B.; 2005: Spatial variation of seismogenic stress orientations in Sicily, south Italy. Physics of the Earth and Planetary Interiors, 148, 175-191.

QUADRO CINEMATICO ATTUALE DELL’ITALIA CENTRO-SETTENTRIONALE N. Cenni1, E. Mantovani1, P. Baldi2, M. Viti1 , D. Babbucci1 1 Dipartimento Scienze della Terra, Università degli Studi di Siena 2 Dipartimento di Fisica, Università degli Studi di Bologna

L’attuale quadro cinematico presente nell’Italia centro – settentrionale può essere ricostruito con una buona risoluzione spaziale utilizzando le stazioni GPS permanenti installate per studi di carattere scientifico. In questo studio verranno presentati i risultati ottenuti elaborando i dati forniti da 81 stazioni scientifiche, acquisiti dagli archivi informatici dell’ASI, INGV–RING, EUREF, FRED- NET e Rete Toscana, e di 112 stazioni commerciali appartenenti alle seguenti agenzie pubbliche e

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GNGTS 2009 SESSIONE 1.2 private: Arpa Piemonte, ASSOGEO, IREALP, LABTOPO, Regione Veneto, Regione Abruzzo e SOGER. L’analisi dati è stata eseguita utilizzando il software GAMIT/GLOBK seguendo la procedura denominata distributed processing (Dong et al., 1998), che consente di analizzare reti con un alto numero di stazioni suddividendole in diverse sotto – reti distinte (cluster). Per questo motivo, le osservazioni delle diverse stazioni, relative al periodo 1 gennaio 2001 – 30 Agosto 2009, sono state suddivise in 9 diversi cluster, all’interno dei quali sono state sempre incluse anche le osservazioni di 5 siti IGS/EUREF: CAGL, GRAZ, MATE, WTZR e ZIMM, le cui posizioni e velocità IGS sono state usate per allineare la soluzione globale nel sistema di riferimento ITRF2005 mediante una roto – traslazione. L’installazione delle stazioni commerciali avviene solitamente seguendo pro- tocolli per la scelta dei siti e per l’installazione dei supporti dell’antenna diversi da quelli adottati per i siti scientifici. Questo, nel caso si voglia utilizzare le osservazioni commerciali per studi di carattere scientifico, introduce la necessità di verificare se queste metodologie non introducano nuove sorgenti di rumore nei dati o aumentino quelle già esistenti. Da questa analisi è emerso che le caratteristiche delle serie temporali della posizione giornaliera delle stazioni commerciali sono simili a quelle dei siti scientifici come dimostrato in alcuni recenti lavori (Baldi et alii 2009a, D’Agostino et alii 2008) e nella nota presentata da Cenni et alii (Baldi et alii 2009b). La Fig. 1 mostra l’attuale quadro cinematico ottenuto considerando tutti i siti scientifici e commerciali con un periodo di osservazione superiore ad 1 anno. Alcuni autori (Blewitt e Lavallée 2002) ritengono che solo i risultati provenienti da stazioni con un periodo di osservazione superiore a 2.5 anni siano attendibili e utilizzabili per studi di carattere tettonico. Per questo motivo nella Fig. 1, le velocità delle stazioni con un periodo di osservazione superiore ai 2.5 anni sono state riportate con un simbolo più spesso. Le stazioni situate nella parte centrale della catena appennica compresa la sua parte sepolta sotto la Pianura Padana (Fig. 1), sono caratterizzate da una velocità di circa 3-4 mm/anno, generalmente superiore a quelle dei siti ubicati nella parte settentrionale ed interna della catena (Fig. 1). In parti-

Fig. 1 – Quadro cinematico attuale nell’Italia centro – settentrionale. I vettori indicano le velocità residue dei diversi siti nel sistema di riferimento ITRF2005 rispetto ad una placca eura- siatica stabile, modellata utilizzando il polo di rotazione proposto da Altamini et alii 2007. I vettori più spessi rappresentano le velocità delle si riferiscono ad un periodo di osservazione superiore ai 2.5 anni, mentre quelli più sottili rappresentano la cinematica dei siti con un periodo di osservazione tra 1 anno e 2.5 anni. AS = Appennino Settentrionale; AC = Appennino Centrale; LA = Piattaforma Laziale-Abruz- zese; ML = Monti della Laga; PP = Pianura Padana.

155 GNGTS 2009 SESSIONE 1.2 colare, le stazioni poste nella piattaforma Laziale-Abruzzese e dei Monti della Laga (Fig. 1) presentano velocità significativamente più elevate (5-8 mm/anno) rispetto a quelle delle zone circostanti. Considerato l’intervallo di osservazione relativamente breve preso in considerazione per il momen- to, il risultato sopra citato va preso come preliminare. Nella nota verranno presentati i primi risultati relativi al campo di deformazione regionale associato al campo di velocità di Fig. 1 calcolato utilizzando una procedura agli elementi finiti. Ringraziamenti. Si ringraziano le seguenti istituzioni pubbliche: Regione Abruzzo, Regione Veneto e l’Arpa Piemonte e gli enti commerciali: ASSOGEO, IREALP, LABTOPO e SOGER per aver gentilmente messo a disposizione della comunità scientifica le loro banche dati. Un particolare ringraziamento va al personale ASSOGEO e della Regione Abruzzo per la loro disponibilità nel recupero dei dati non presenti in linea. Inoltre si ringrazia l’Ufficio Tecnico del Genio Civile della Regione Toscana per il supporto dato nella realizzazione della Rete della Toscana. Bibliografia Altamimi, Z., Collilieux, X., Legrand, J., Garayt, B., Boucher, C.; 2007. ITRF2005: a new release of the International Terrestrial Reference Frame based on time series of station positions and Earth Orientation Parameters. J. Geophys. Res. 112, B09401. doi:10.1029/2007JB004949. Blewitt, G., Lavallée, D.; 2002: Effect of annual signals on geodetic velocity. J. Geophys. Res. 107(B7), 2145, doi:10.1029/2001JB000570. Baldi P., Casula G., Cenni N., Loddo F., Pesci A.; 2009a: GPS-based monitoring of land subsidence in the Po Plain (Northern Italy). Earth Planet. Sci. Lett., doi:10.10016/j.epsl.2009.09.023. Baldi P., Casula G., Cenni N., Loddo F., Pesci A.; 2009b: La subsidenza nell’Italia Centro – Settentrionale da misure GPS. 28° Convegno Nazionale G.N.G.T.S. Trieste 16 – 19 novembre 2009. D’Agostino, N., Avallone, A., Cheloni, D., D’Anastasio, E., Mantenuto, S., Selvaggi, G.; 2008: Active tectonics of the Adriatic region from GPS and earthquake slip vectors. J. Geophys. Res., 113: B12413, doi:10.1029/2008JB005860. Dong, D., Herring, T.A., King, R.W.; 1998: Estimating regional deformation from a combination of space and terrestrial geodetic data. J. Geod., 72: 200–214. Viti M., Mantovani E., Cenni N., Babbucci D.; 2009: Strain rate field from geodetic velocity measurements: an approach based on numerical modelling. Il Quaternario, 22, 109-116.

SISMICITÀ ALL’ETNA TRA LUGLIO 2005 E GENNAIO 2006: EVIDENZE DI INTRUSIONE MAGMATICA E DI DINAMICA DI FIANCO O. Cocina1, G. Barberi1, E. Giampiccolo1, V. Milluzzo2, C. Musumeci1, D. Patanè1 1 Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Catania 2 Eni S.p.A. – Divisione Exploration & Production, San Donato Milanese, Milano

Nel presente lavoro sono presentati i risultati di uno studio della sismicità dell’Etna registrata tra luglio 2005 e gennaio 2006. Durante tale periodo l’integrazione dei dati provenienti da un esperi- mento condotto attraverso l’impiego di 20 stazioni temporanee a larga banda in aggiunta alla rete permanente, costituita da 40 stazioni, ha permesso di ottenere migliori localizzazioni ipocentrali (maggior numero di letture P ed S, riduzione degli errori ipocentrali e del gap azimutale). Ciò ha consentito analisi di maggior dettaglio anche degli eventi a più bassa magnitudo (M<2.0) che costi- tuiscono il 75 % del campione. In particolare, si è proceduto alla rilocalizzazione degli eventi (Fig. 1) utilizzando il modello di velocità 3D di Patanè et al. (2006) e al calcolo dei meccanismi focali. La maggior parte della sismicità è localizzata sul fianco orientale del vulcano permettendo una più accurata interpretazione della dinamica di questo settore. Inoltre, la localizzazione 3D dei terremoti ha meglio evidenziato l’attività sismica lungo il Rift meridionale del vulcano relativa ad uno scia- me profondo (tra 10 e 15 km) registrato nell’agosto del 2005, probabilmente correlata ad una intrusione magmatica. Infatti, tale sismicità è stata seguita nei mesi successivi da un forte incremento del tremore che, tuttavia, non ha portato nel breve termine ad alcuna eruzione. Ciò nonostante, è stato osservato che in altri periodi la sismicità lungo questo trend strutturale ha preceduto di alcuni mesi l’attività eruttiva (2001, 2002-2003 e 2008).

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Fig. 1 - Mappa epicentrale 3D della sismicità analizzata. In grigio chiaro tutta la sismicità analizzata. In grigio scuro gli epicentri relativi ai meccanismi focali selezionati.

Bibliografia Patane`, D., Barberi G., Cocina O., De Gori P., Chiarabba C.; 2006: Time-Resolved Seismic Tomography Detects Magma Intrusions at Mount Etna. Science, 313, 821-823.

ABRUZZO (ITALY) EARHQUAKES OF APRIL 2009: HETEROGENEOUS FAULT SLIP MODELS AND STRESS TRANSFER FROM ACCURATE INVERSION OF ENVISAT-DINSAR DATA G. De Natale1, B. Crippa2, C. Troise1, F. Pingue1, K. Audia3, G. Dalla Via2 1 INGV-Osservatorio Vesuviano, Naples, Italy 2 University of Milan, Italy 3 University of Trieste, Italy

The seismic sequence occurred in the Abruzzo Apennines near L’Aquila (Italy) in April 2009 caused extensive damage and a large number of casualties (close to 300). The earthquake struck an area in the Italian Apennines chain where several faults, belonging to adjacent seismotectonic domains, create a complex tectonic regime resulting from the interaction among regional stess build-up, local stress changes caused by individual earthquakes and visco-elastic stress relaxation. Understanding such complex interaction in the Apennines can lead to a large step forward in the seismic risk mitigation in Italy. The Abruzzo earthquake has been exceptionally well recorded by InSAR data, much better than the first Italian earthquake ever recorded by satellites, namely the 1997 Umbria-Marche one. Envisat data for the Abruzzo earthquake are in fact very clear and allow an accurate reconstruction of the faulting mechanism. We present here an accurate inversion of vertical deformation data obtained by ENVISAT images, aimed to give a detailed reconstruction of the fault geometry and slip distribution. The resulting faulting models are then used to compute, by a suitable theoretical model based on elastic dislocation theory, the stress changes induced on the neighbouring faults. The figure reports the best variable slip model for this earthquakes, including

157 GNGTS 2009 SESSIONE 1.2

Fig. - Best fitting variable slip fault model for the April 6 and 7 mainshocks of the 2009 L’Aquila earthquake sequence, as inferred from inversion of DInSAR data. Also shown is a depth section orthogonal to the fault plane, showing the relative location of the two mainshocks with respect to modelled fault plane. section showing the position of the two mainshocks of April 6 and 7 relative to the fault plane. A striking observation is that both the earthquakes appear located deeper than the significantly slipped areas. The study of the mainshocks sequence of the Abruzzo earthquakes clearly evidence the effect of static stress changes consecutively triggering the subsequent mainshocks. Furthermore, this analysis put in evidence the seismotectonic domains that have been more heavily charged by stress released by the Abruzzo mainshocks. The most important faults significantly charged by the Abruzzo sequence include the Sulmona and Avezzano tectonic domains. Taking into account the average regional stress build-up in the area, the positive Coulomb stress changes caused by this earthquake can be view as anticipating the next earthquakes in the neighbouring domains of some tens of years.

STRUCTURAL AND GEOPHYSICAL CONSTRAINTS RELATIVE TO A “TRASCURRENT BELT”: A NEW POSSIBLE INTERPRETATION ABOUT THE FORMATION OF THE NORTHERN/CENTRAL APENNINES? F.M. Elter1, P. Elter2, C. Eva1, E. Eva 3, R.K. Kraus1, M. Padovano1, S. Solarino3 1 Dip.Te.Ris., Università di Genova, Genova 2 Località Val di Vico, Calci, Pisa 3 Istituto Nazionale di Geofisica e Vulcanologia, CNT, c/o Dip.Te.Ris., Genova

The North-Central Apennines regional stress field, responsible for the development and evolution of the Quaternary Shear Frame (QSF), is characterized by a NW-SE compression and by a NE- SW extension (Favali et al., 1993, Cello et al., 1997, Boncio and Lavecchia, 2000, Pizzi and Galadini, 2009). A coeval NE-SW (“Tettonica Trasversale”) and NW-SE line system is recognizable in the North-Central Apennines. The “Tettonica Trasversale” (Elter, 1960, Bortolotti, 1966, Castellarin et al., 1978, Fazzini and Gelmini, 1982) or persistent structural barriers (Pizzi and Galadini, 2009) is characterized by a set of NE-SW kilometric lines that cuts the North Apenninic belt. Moving from Northwest towards Southeast, the best known persistent structural barriers are:

158 GNGTS 2009 SESSIONE 1.2 the Taro Line (TL, or Passo del Bracco-Parma, Fazzini and Gelmini, 1982), the La Spezia-Reggio Emilia-Concordia Line (SRECL, Fazzini and Gelmini, 1982), the Secchia Line (SL, Fazzini and Gelmini, 1982), the Livorno-Sillaro Line (LSL, Eva et al., 2005, Dellisanti et al., 2008), the Arbia- Val Marecchia Line (AML, Liotta, 1991), the Vicchio fault system, (VFS, Sani et al., 2009), the Monte Cavallo Thrust (MCT, Pizzi and Galadini, 2009), the Olevano-Antrodoco-Sibillini Mounts thrust (OAST, Pizzi and Galadini, 2009) or Ancona-Anzio Line (AAL, Castellarin et al., 1978) and the Sangro-Volturno thrust (SVTZ, Pizzi and Galadini, 2009) or Roccamonfina-Ortona Line (ROL, Favali et al., 1993). The kinematic of some of these lines is composite: the TL and SRECL, are sinistral strike-slip shear zones (Fazzini and Gelmini, 1982), the LSL is actually interpreted as a system of strike slip or transpressive faults (Bortolotti, 1966); the AML acted as dextral transfer fault (Fazzini and Gelimini, 1982) on the western side and as lateral ramp on the eastern side (Liotta, 1991). The kinematic of the OAST or AAL is actually controversial: sinistral strike-slip shear zone according to Castellarin et al. (1978), dextral strike-slip for Fazzini and Gelmini (1982) and Favali et al. (1993) and a reverse shear zone for Pizzi and Galadini (2009). Also the SVTZ (or ROL) is considered as dextral strike-slip shear zone by Favali et al (1993) and as a reverse shear zone by Pizzi and Galadini (2009). Kilometric NW-SE Lines are, for example, the Groppodalosio- Compione and Arzengio-Ceretoli faults (Bernini, 1988), the Sieve-fault - Ronta Fault system (Sani et al., 2009), the Alto Tiberina fault (Collettini et al., 2000). The kinematic of these lines is always composite and is characterized by the coeval presence of sinistral strike-slip shear zones and normal shear zones (Bernini, 1988, Favali et al., 1993, Cello et al., 1997, Martini et al., 2001, Sani et al., 2009). The complex pattern of coeval strike-slip and normal shear zones has already been observed, at a smaller scale, in the L’Aquila area (Kraus et al., 2009). In the model suggested by these authors, the pattern of “snake” shear zones enhances the formation of pull-apart and coeval pop-up structures. In more details, the model suggested for the L’Aquila by Kraus et al. (2009), is characterized by: 1. normal faults oriented NW-SE; 2. imposed “snake” sinistral stike-slip shear zones oriented NNW-SSE (persistent structural barriers); 3. “snake” R- synthetic strike-slip faults oriented NW-SE coeval with restraining/releasing bends; 4. R’- antithetic oblique dextral strike-slip faults oriented WNW-ESE coeval with the NW-SE, R- synthetic strike-slip faults. In the present study we discuss the applicability of the model to a larger scale for the whole Apenninic chain. In the North-Central Apennines, many pull-apart basins (formerly “intramontane basins”) are recognizable and they are generally related to NW-SE sinistral strike-slip faults and NW-SE normal fault. Moving from SE towards NW, they are: the Avezzano basin (Martini et al., 2001), the Aquila basin (Cello et al., 1997); the Cascia basin: (Cello et al., 1997); the Norcia basin, (Cello et al., 1997); the Colfiorito basin, (Boncio and Lavecchia, 2000); the Arezzo-San Sepolcro basins, (Sani et al., 2009); the Firenze-Pistoia and the Mugello-Casentino basins (Sani et al., 2009); the Altopascio basin (Cantini et al., 2001); the Barga basin, (Coltorti et al., 2008); the Garfagnana- Serchio basin, (Luzi et al., 2000); the Sesta Godano basin, (Galadini et al., 2000) and the Lunigiana graben, composed by two fluvio-lacustrine basins, the Compiano-Pontremoli basin to the northwestern and the Aulla-Olivola to the southeastern, (Bernini, 1988, Bernini and Papani, 2002). Despite of the good knowledge about pull-apart basins, few data can be found in bibliography about the restraining bends or pop-up structures. Only in the Southern Apennines, Cello and Mazzoli (1999) have shown the presence of “push-ups” structures between WNW-ESE en-echelon left-lateral strike-slip, restraining bend and contractional structures at fault termination in the Calabria- Lucania borderland. Favali et al., 1993 consider the Tremiti Islands as a push-up structure too. Kraus et al. (2009) hypothesized that other pop-up structures are recognizable into the Central Apennines: the Maiella Massif (MM) and some minor pop-up structures in the Sannio-Molise Unit

159 GNGTS 2009 SESSIONE 1.2 could in fact represent these restraining bends. Ciaccio and Chiarabba (2002), delineate in the North Apennines, a pop-up structure in the center of the Emilian arc at 6-14 km depth, namely the Bagnolo structural high. It is composed by shelf limestones of Early Cretaceous and analogous limestones of the late Jurassic, decolled and thrust over the Neogenic formations belonging to the foredeep. From the seismological point of view the Northern and Central Apennines are characterized by instrumental seismicity of moderate to intermediate magnitudes up to 6.0 (Gruppo di lavoro CPTI, 1999). Seismic events are generally concentrated in the first 20 km depth (Frepoli and Amato, 1997). The focal solutions of the principal events show great complexity; the most recent strong earthquakes show normal mechanisms in the central Apennines (Umbria-Marche 1997, (Morelli et al., 2000) and Aquila 2009, (http://portale.ingv.it/primo-piano/archivio-primo-piano/notizie- 2009/terremoto-6-aprile/meccanismi-focali)), both reverse (Reggio Emilia, 1996 (Selvaggi et al., 2001)) and strike-slip solutions (Ancona 1972, (Gasparini et al., 1985) and Ancona 2009, (http://mednet.rm.ingv.it/procedure/events/QRCMT/090920_035016/qrcmt.gif)) in the Northern Apennines. The analysis of the minor seismicity indicates a similar trend with marked non-homo- geneities in the focal solutions (Frepoli and Amato, 1997; 2000; Eva et al., 2005). However the orientations of the principal stress axes, as computed from the focal solutions, reveal a sigma 3 oriented NE-SW / ENE-WSW, except for the northern sector where, on the basis of the orientation of sigma 1 and sigma 2 axes, a strike slip stress regime prevails (Frepoli and Amato, 2000), as also confirmed by borehole breakout analysis (Montone et al. ,1995). Thus the seismological evidences confirm a NE-SW extension, in agreement with the model proposed in this study for the North- Central Apennines. In particular in the Western part of the Northern Apennines the “persistent structural barriers” perfectly mimic the seismicity. In the Northern sector, a line northern of the Taro river acts as the limit of the consistent seismicity of the chain; conversely, the southern limit is the Livorno-Sillaro, acting as a transfer zone close to the high heat flux area of Larderello (Eva et al., 2005). It has to be remarked that the complexity of the stress regime in this part of the chain lies in its different behaviour with depth. In fact, the orientation of the principal stress axes turns from transtensive at a depth 0-10 km to transpressive below 10 down to 30 km depth (Eva et al., 2005). The interpretation of both geological and seismological aspects leads to underline the fundamental role played by the system of shear zones, and allows us to propose the Apennines Belt (North and Central sectors) as a Transcurrent Belt (Padovano et al., 2009). These kind of belts are characterized by “bowed” morphology, coeval presence of restraining and releasing bends, a relevant seismicity and the lack of a typical High Pressure and/or High Temperature overprinting. References Bernini M., 1988: Il Bacino dell’Alta Val di Magra: primi dati mesostrutturali sulla tettonica distensiva. Bollettino della Società Geologica Italiana, 107, 355-371. Bernini M., Papani G., 2002: La distensione della fossa tettonica della Lunigiana nord-occidentale. Bollettino Società geologica Italia, 121/3, 313-341. Boncio P., Lavecchia G., 2000: A geological model for the Colfiorito earthquakes (September-October 1997, central Italy). Journal of Seismology, 4, 345–356. Bortolotti V., 1966: La tettonica trasversale dell’Appennino I - La linea Livorno-Sillaro. Bollettino della Società Geologica Italiana, 85, 529-540. Cantini P., Testa G., Zanchetta G., Cavallini R., 2001: The Plio–Pleistocene evolution of extensional tectonics in northern Tuscany, as constrained by new gravimetric data from the Montecarlo Basin (lower Arno Valley, Italy). Tectonophysics 330, 25–43. Castellarin A., Colacicchi R., Praturlon A., 1978: Fasi distensive, trascorrenze e sovrascorrimenti lungo la linea “Anzio-Ancona” dal Lias Medio al Pliocene. Geologica Romana, 17, 161-190. Cello G., Mazzoli S., 1999: Apennine tectonics in southern Italy: a review. Geodynamics, 16, 191-211. Cello G., Mazzoli S., Tondi E., Turco E., (1997: Active tectonics in the central Apennines and possible implications for seismic hazard analysis in peninsular Italy. Tectonophysics 272, 43-68. Ciaccio M.G., Chiarabba C., 2002) Tomographic models and seismotectonics of the Reggio Emilia region, Italy. Tectonophysics 344, 261– 276. Collettini C., Barchi M., Pauselli C., Federico C., Pialli G., 2000: Seismic expression of active extensional faults in northern Umbria (Central Italy). Journal of Geodynamics, 29, 309-321. Coltorti M., Pieruccinia P., Rustioni M., 2008: The Barga Basin (Tuscany): A record of Plio-Pleistocene mountain building of the Northern Apennines, Italy Quaternary International, 189, 56–70.

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Dellisanti F., Pini G.A., Tateo F., Baudin F., 2008: The role of tectonic shear strain on the il-litization mechanism of mixed-layers illite–smectite. A case study from a fault zone in the Northern Apennines, Italy, Geol Rundsch, 97, 601–616. Elter P., 1960: I lineamenti tettonici dell’Appennino a nord ovest delle Apuane. Bollettino Società Geologica Italiana, 79. Eva E., Ferretti G., Solarino S., 2005: Superposition of different stress orientations in the western sector of the northern Apennines (Italy) Journal of Seism., 9, 413-430. Favali P., Funiciello R., Mattietti G., Mele G., Salvini F., 1993: An active margin across the Adriatic Sea (central Mediterranean Sea). Tectonophysics, 219, 109-117. Fazzini P., Gelmini R., 1982: Tettonica trasversale nell’Appennino Settentrionale. Memorie della Società Geologica Italiana, 24, 299-309. Frepoli A., Amato A., 1997, Contemporaneous extension and compression in the Northern Apennines from earthquake fault plane solutions. Geophys. J. Int., 129, 368-388. Frepoli A., Amato A., 2000, Spatial variations in stresses in peninsular Italy and Sicily from background seismicity. Tectonophysics, 317 (1) 109-124. Galadini F., Meletti C., Vittori E., 2000: Stato delle conoscenze sulle faglie attive in Italia: elementi geologici di superficie. Risultati del progetto 5.1.2 “Inventario delle faglie attive e dei terremoti ad esse associabili”, 1-30. Gasparini C., Iannaccone G., Scarpa R., 1985, Fault-plane solutions and seismicity of the Italian peninsula. Tectonophysics, 117, 59-78. Gruppo di lavoro CPTI, 1999, Catalogo Parametrico del Terremoti Italiani. ING, GNDT, SGA, SSN, Bologna. Kraus R.K. , Elter F.M. , Eva C., Eva E., Padovano M, Solarino S., 2009: An alternative interpretation for the seismic sequence of the L’Aquila earthquake: a combination between imposed strike-slip system and strain ellipse frame. In: 28° GNGTS, Sessione SPECIALE: Il terremoto dell’Abruzzo. Liotta D., 1991: The Arbia - Val Marecchia Line, Northern Apennines. Eclogae Geol. Helv., 84/2, 413-430. Luzi L., Pergalani F., Terlien M.T.J., 2000: Slope vulnerability to earthquakes at subregional scale, using probabilistic techniques and geographic information systems. Engineering Geology 58, 313–336 . Martini P. I., Sagri M., Colella A., 2001: Neogene-Quaternary basins of the inner Apennines and Calabrian arc. In: Anatomy of an Orogen: the Apennines and Adjacent Mediterranean Basins, Vai G.B., Martini P. I. (eds), Kluwer Academic publisher, 375-400. Montone P., Amato A., Chiarabba C., Buonasorte G., Fiordelisi A., 1995, Evidence of active extension in Quaternari volcanoes of Central Italy from breakout analysis and seismicity. Geophys. Res. Lett., 22 (14), 1909-1912. Morelli A., Ekström G., Olivieri M., 2000, Source properties of the 1997-98 Central Italy earthquake sequence from inverions of long-period and broad-band seismograms. Journal of Seismology, 4 (4), 365-375. Padovano, M., Kraus, R., Elter, F.M., 2009. The Sardinian Variscan Mantle Gneiss Dome: a pop-up structure emplaced along the eastern Gondwana boundary? In: VII Forum di Scienze della Terra – Geoitalia 2009- Simposium Geodinamica e Petrogenesi, H 1- Approcci multidisciplinari per la ricostruzione ed interpretazione tettonica delle traiettorie P-T-t, Epitome 3, 187-188. Pizzi A., Galadini F., 2009: Pre-existing cross-structures and active fault segmentation in the northern-central Apennines (Italy). Tectonophysics, doi:10.1016/j.tecto.2009.03.018. Sani F., Bonini M., Piccardi L., Vannucci G., Delle Donne D., Benvenuti M., Moratti G., Corti G., Montanari D., Sedda L., Tanini C., 2009: Late Pliocene-Quaternary evolution of outermost hinterland basins of the Northern Apennines (Italy), and their relevance to active tectonics. Tectonophysics, :10.1016/j.tecto.2008.12.012. Selvaggi G., Ferulano F., Di Bona M., Frepoli A., Azzara R., Basili A., Chiarabba C., Ciaccio M.G., Di Luccio F., Lucente F.P., Margheriti L., Nostro C., 2001, The Mw 5.4 Reggio Emilia 1996 earthquake: active compressional tectonics in the Po Plain, Italy. Geophys. J. Int., 144, 1-13.

EVIDENZE DI FAGLIAZIONE NORMALE TARDO-OLOCENICA NEL SETTORE COMPRESO FRA LA CONCA SUBEQUANA E LA MEDIA VALLE DELL’ATERNO, A SUD DELL’AREA EPICENTRALE DEL TERREMOTO DI L’AQUILA DEL 6 APRILE 2009: IMPLICAZIONI SISMOTETTONICHE E. Falcucci1, S. Gori1, M. Moro2, F. Galadini1, S. Marzorati1, C. Ladina1, D. Piccarreda1, P. Fredi3 1 Istituto Nazionale di Geofisica e Vulcanologia, Milan-Pavia 2 Istituto Nazionale di Geofisica e Vulcanologia, Centro NazionaleTerremoti 3 Dipartimento di Scienze della Terra, Università degli Studi di Roma “La Sapienza,” La conca Subequana costituisce una delle depressioni intermontane più orientali dell’Appennino abruzzese, situata a sud delle conche di L’Aquila e di Fossa-San Demetrio. L’evoluzione e l’asset- to strutturale della conca Subequana sono stati condizionati dall’attività di un sistema di faglie che interessano il margine orientale della depressione e che sono individuabili lungo il versante occidentale del Monte Urano-Le Serre. Tale sistema di faglie, con direzione NW-SE, si segue con una certa continuità per circa 8-10 km. Questa struttura tettonica, caratterizzata da una evoluzione strutturale complessa, è stata interessata da movimenti prevalentemente distensivi nel corso del

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Fig. 1 – Parete di una delle trincee geognostiche scavate lungo un segmento del sistema di faglia che borda la conca Subequana. Le frecce indicano i piani di taglio che interessano depositi.

Quaternario, testimoniati dalla dislocazione di depositi continentali pleistocenici (Miccadei et al., 1997). Sono stati effettuati rilevamenti geologici e geomorfologici all’interno del bacino, con particolare riguardo alla zona del versante del monte Urano, finalizzati all’individuazione di elementi utili alla definizione dell’attività tardo-pleistocenica-olocenica di tale elemento tettonico. A tal fine sono state effettuate delle trincee geognostiche che hanno permesso di individuare la dislocazione di depositi riferibili ad un contesto cronologico relativo all’Olocene (con un evento di fagliazione in superficie posteriore a 2615±19BP), definendo così l’attività della struttura tettonica (Fig.1). Inoltre, le osservazioni effettuate hanno permesso di individuare elementi strutturali orientati NE- SW, dunque trasversali al sistema di faglie analizzato, localizzati nel settore compreso fra la conca Subequana e la terminazione meridionale della Valle dell’Aterno, nello specifico nell’area compresa fra i paesi di Castelvecchio Subequeo e Molina Aterno. Questi elementi strutturali sono responsabili della dislocazione di depositi fluviali, individuabili in destra idrografica del fiume Aterno, a poche centinaia di metri a sud di Molina Aterno. Anche se tali depositi non sono stati ancora cro- nologicamente vincolati, la loro dislocazione lungo queste faglie trasversali indica l’attività quaternaria (probabilmente tardo-quaternaria) di questi elementi tettonici. Tali osservazioni suggeriscono che queste faglie trasversali rappresentino delle trasfert faults (e.g. Peacock, 2002) che collegano il sistema di faglie del bacino subequano con quello della media Valle dell’Aterno, quest’ultimo già riconosciuto da diversi autori (e.g. Galadini e Galli, 2000). Inoltre, nell’ottica di ottenere maggiori informazioni sull’evoluzione quaternaria della conca Subequana, è stata condotta una campagna di misure di noise sismico ambientale nel bacino, volta ad indagare l’andamento profondo dell’interfaccia substrato carbonatico-riempimento continentale. I risultati ottenuti attraverso la tecnica dei rapporti spettrali HVSR di Nakamura, mostrano chiari picchi spettrali grazie al forte contrasto di impedenza tra i depositi quaternari ed il substrato calca- reo. In particolare, lo spostamento della frequenza fondamentale di vibrazione dei sedimenti indica un approfondimento del bacino della zona tra Castel di Ieri e Castelvecchio Subequo. Tale assetto sarebbe paragonabile a quello osservato nelle depressioni tettoniche adiacenti del Fucino (Galadini e Messina, 2001) e della conca di Sulmona (Miccadei et al., 1998). Questo per- metterebbe di ipotizzare un’evoluzione tettonica simile di questi bacini.

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Bibliografia Galadini F, Galli P (2000) Active tectonics in the central Apennines (Italy) – Input data for seismic hazard assessment. Nat Hazards 22:225-270. Galadini F, Messina P (2001) Plio-Quaternary changes of normal fault architecture in the central Apennines (Italy). Geodinamica Acta 14:321-344. Miccadei E, Barberi R, De Caterini G (1997) Nuovi dati geologici sui depositi quaternari della conca Subequana (Appennino abruzzese). Il Quaternario 10(2), 485-488. Miccadei E, Barberi R, Cavinato GP (1998) La geologia quaternaria della conca di Sulmona (Abruzzo, Italia centrale). Geol Romana 34:59-86. Peacock DCP (2002) Propagation, interaction and linkage in normal fault systems. Earth-Science Rev 58:121-142.

MODELLI ALTERNATIVI PER LA SISMOTETTONICA DEL MARGINE ALPINO LIGURE F. Fanucci 1, S. Migeon 2, C. Larroque 2, A. Cuppari 1, N.Corradi 3, D. Morelli 1 1 DISGAM – Università di Trieste 2 Geoscience Azur – Nizza 3 DIPTERIS – Università di Genova

Nuove indagini di morfobatimetria multibeam e sismica a riflessione ad alta risoluzione, condotte nell’ambito del Progetto franco-italiano MALISAR, consentono di porre alcuni vincoli alle interpretazioni e modellazioni riguardanti la sismotettonica del margine continentale ligure di ponente. Esso è limitato ad est dalla imponente scarpata di faglia che costituisce il limite tra bacini del Mediterraneo Occidentale e sistema tirrenico. Essa interferisce con le direttrici appenniniche del margine di levante dando luogo ad una concentrazione di eventi sismici riconducibili a strutture dirette e/o trascorrenti. Ben più complessa è l’attività delle altre parti del margine, diffusa e a caratteri fortemente variabili, che si concentra maggiormente nel settore occidentale (Fig. 1). I meccanismi focali noti non sono moltissimi, ma diversificati: prevalgono trascorrenza e traspressione, con singoli eventi le cui soluzioni si avvicinano alla compressione pura (Fig. 2). La struttura superficia-

Fig. 1 – Sismi- cità delle Alpi Liguri e del loro margine.

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Fig. 2 – Meccani- smi focali dei principali eventi.

le di questa parte del margine è determinata da step-faults che conferiscono ripidità alla scarpata continentale, intersecate da numerose faglie normali alla costa, talune in continuità con linee emerse, a cinematica prevalentemente disgiuntiva o trascorrente, mentre i meccanismi focali di tipo opposto competono agli eventi sismici di maggiore profondità ubicati al piede della scarpata o in posizione ancora più distale. Per tentare di conciliare fatti apparentemente così discordi è stato ela- borato un modello che propone una ripresa in compressione di un originario margine passivo per attivazione di una superficie di scorrimento profonda, in pratica coincidente con la Moho, che por- terebbe la crosta europea a sovrapporsi a quella del Bacino Ligure. Il meccanismo di attivazione sarebbe sostanzialmente lo stesso (spinta da N) che ha portato nel Plio-Pleistocene i massicci cri- stallini esterni delle Alpi Marittime (Argentera-Mercantour) ad accavallarsi verso S, sollecitando la deformazione delle coperture sedimentarie del basamento provenzale (Fig. 3) Risentirebbe di questa dinamica, sia pure in misura attenuata, anche il settore occidentale del margine in questione che, però, presenta un assetto morfostrutturale alquanto diverso. I dati più recenti presentano alcune sostanziali novità sulla strutturazione ed evoluzione del margine, ma non

Fig. 3 – Modello geodinamico di Courboulex et alii (2003).

164 GNGTS 2009 SESSIONE 1.2 rilevano alcun dato decisivo in favore o contro il modello citato. Considerando che la sismicità del tipo detto non interessa solo il margine, ma anche il retroterra ed il Bacino stesso con analoga frequenza e intensità, è possibile formulare un modello alternativo che ammette una riattivazione di Bacino e margine settentrionale nel contesto della convergenza Africa-Europa, con il Blocco Corso- Sardo nel ruolo di trasferitore delle spinte, prevalentemente orientate SE-NW. Ne risulterebbe una riattivazione delle trascorrenti crostali che hanno determinato la genesi del Bacino e delle linee che segmentano il basamento bacinale, orientando SW-NE i cosiddetti “muri di sale”, strutture diapiri- che a simmetria cilindrica orizzontale. Le varie modalità di interazione tra le linee dette e quelle caratterizzanti il margine possono dar conto delle soluzioni focali note. Gli effetti del processo detto sarebbero prevalentemente di natura traspressiva come indicano recenti rielaborazioni dei dati sismici più significativi. Bibliografia Bigot-Cormier F., Sage F., Sosson M., Déverchère J., Ferrandini M., Guennoc P., et l’équipe CYLICE, (2004). Déformations pliocènes de la marge nord-Ligure: les conséquences d’un chevauchement crustal sud-alpin, Bull. Soc.Géol. Fr., 175, 2, 197-211. Courboulex F., Larroque C., Deschamps A., Gélis C., Charreau J. and J.F. Stéphan. (2003). Hidden faulting revealed by microseismicity in the south-east of France Geophys. Res. Lett., 30(15), 1782, doi:10.1029/2003GL017171. Fanucci F. & Nicolich R. (1984). Il Mar Ligure: nuove acquisizioni sulla naturagenesi ed evoluzione di un “Bacino marginale”. Mem. Soc. Geol. It., 27: 97-110. Fanucci F., Firpo M. (1992) - Structural model of Italy (Sheets 1-3, marine areas). C.N.R., P. F. Geodinamica, Sottoprogetto Modello Strutturale Tridimensionale. FanucciI F. , Morelli D. (1994) – Principali limeamenti strutturali ed evoluzione del Mar Ligure (Mediterraneo Occidentale). Atti XI Congresso A.I.O.L.:793-806 Larroque C., Béthoux N., Calais E., Courboulex F., Deschamps A., Déverchère J., Stéphan J.F., Ritz J.F. and Gilli E. (2001). Active deformation at the junction between southern French Alps and Ligurian basin. Netherlands Journal of Geosciences, 80, 255-272.

STRUCTURAL EVOLUTION AND ACTIVE TECTONICS IN THE SOUTHERN TARANTO GULF: INSIGHTS FROM SEISMIC REFLECTION PROFILES ANALYSIS L. Ferranti1, M. E. Mazzella1, D. Morelli2 1 Dipartimento di Scienze della Terra, Università di Napoli, Italy 2 Dipartimento di Scienze Geologiche, Ambientali e Marine, Università di Trieste, Italy

Analysis of offshore seismic profiles and morphobathymetric data, supplemented by local network seismicity, provides insights into the recent structural evolution and active strain field that affects northeastern Calabria, a region of weak seismicity. Onland this region, Middle Pleistocene waning of Miocene-Early Pleistocene thin-skinned frontal thrust belt motion was coeval to onset of regional uplift, which is documented by flights of raised marine terraces (Cucci & Cinti, 1998; Santoro et al., 2009; Ferranti et al., 2009) and is commonly attributed to deep sources. Offshore, motion of the thrust belt might have continued in the Pleistocene, when it was replaced by thick- skin shortening (Doglioni et al., 1999) or strike-slip tectonics (Del Ben et al., 2007), but details are lacking. The study area is centred in the southern part of the Taranto Gulf adjacent to the northern Calabria coast stretching from the borders of the Sila and Pollino mountain ranges and across the Sibari coastal plain. The Miocene-Pliocene fold and thrust belt is cross-cut by steep left strike-slip and transpressional faults mapped both on-land (Catalano et al., 1993; Van Dijk et al., 2000) and offshore (Del Ben et al., 2007), which were active till the Early and perhaps the Middle Pleistocene. The existence of normal faults displacing the marine terraces toward the Ionian Sea was proposed, but is debated (Cucci and Cinti, 1998). The offshore projection of the Pollino morphostructural culmination coincides with the prominent bathymetric high of the Amendolara ridge. Offshore the Sibari plain, a large depoaxes filled by >2.5 km of Pliocene-Quaternary deposits is imaged in the Sibari basin (Fig. 1).

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Fig. 1 – Structural map of the study area (modified after Ferranti et al., 2009).

Our previous work (Ferranti et al., 2009; Santoro et al., 2009) estab- lished that uplift and folding of Pleistocene coastal terraces was partitioned between a regional and a local component, the latter active in a transpressional regime. The faults causing terrace folding can be traced from the coast to offshore the Sibari plain and Pollino and Sila mountain ranges. A numerical modelling of the faults is presented in Santoro et al. (this meeting), whereas this contribution discusses the main results of analysis of publicly available (http://www.socgeol.info/pozzi/ind ex.asp) multichannel seismic reflection profiles (zones D and F and other profiles) supplemented by oil- exploration well logs. The first step in this analysis consisted in the depth conversion of TWT profiles, which was based on a standard but time-consuming velocity analysis. Starting from the velocity readings at individual shot points where available, we computed every 200 ms interval velocity at each point, that was then converted in interval and progressive depths. Manual contouring of isovelocities was then used to create velocity bodies and convert them into depth sections. Identification in the depth profiles of prominent horizons calibrated with exploratory wells allowed to stipulate the vertical displacement rates across faults and folds. Chronostratigraphic and seismic data offer excellent markers that can be laterally traced along the profiles. The best developed reflector is the unconformity which truncates the Messinian (Late Miocene) evaporitic and clastic rocks and forms the base of an unevenly thick Pliocene-Quaternary depositional package. Locally, the abrupt transition between the Lower Pleistocene clay and the overlaying Middle-Upper Pleistocene coarser clastic sequence forms an identifiable reflector which can be used to decipher the more recent structural evolution. Deep reflectors are found in the Apulia carbonate block forming the foreland to the NE and dipping beneath the Apennines and Calabria to the SW. Analysis of a dense grid of seismic profiles (inset in Fig. 1) illustrates that the structural pattern of the SW sector of the Taranto Gulf is dominated by thrusts and transpressional faults that bound structural highs and lows (Fig. 1). The frontal ridge is limited eastward by the markedly curvilinear front of the thin-skinned thrust belt, and is bound to the NE by the low-lying foredeep basin. A satellite basin (Sinni basin) separates the frontal ridge from the more internal and elevated Amendolara ridge (Fig. 1). The structural thickness of the thin-skinned thrust belt increases to the SW from ~2.5 km beneath the frontal high to in excess of 10 km beneath the Amendolara ridge, and is mostly composed of imbricated Miocene and younger deposits. The Apulian carbonate platform, found at the sea-bottom to the NE, plunges southward underneath the foredeep basin and the thrust

166 GNGTS 2009 SESSIONE 1.2 belt, and is itself involved in thrusting. Cross-cutting relations suggests that early shortening was accommodated by gently-dipping, NE-displacing thrusts which repeatedly imbricate the Miocene deposits and, in more internal sectors beneath the Sila coastline, where the thickness of the orogen is in excess of 10 km, the Calabrid and the Apenninic thrust sheets. These thrusts are cut by steeper reverse and transpressional faults which mostly displace to the SW and represent back-thrusts in the regional reference frame (Fig. 1). The backthrusts emanate from underneath the Apulian platform and, at more surficial levels, they branches with several splays within the Messinian evapor- ite, which provides a preferred detachment level. The younger faults clearly truncate the Lower Pleistocene unconformity, and tilting and depoaxial shifts within the Middle-Upper Quaternary package supply further evidence of the recent activity of some faults. Line-balancing techniques indicate that the backthrusts control the present ridge-and-basin morphobathymetric arrangement. Significant back-thrusting has been accommodated on the southern side of the Amendolara ridge, where it controlled the development of a deep (~3 km) through in the Sibari basin, filled by Pliocene-Quaternary deposits. A significant fraction of the vertical offset accommodated along the deformation belt, named Amendolara backthurst fault zone (ABFZ), was accrued during the Pleistocene as suggested by growth relations on the southern side of the ridge. A more internal high (Luana high) is found SW of the Sibari basin, and its NW-SE trend is indicated by alignment of oil drills. In detail, the faults bounding highs and lows have curvilinear traces akin to the pattern which characterizes the fault systems found on-land in the Pollino and Sila ranges (Fig. 1). On the westward sector of the ABFZ close to the coastline, a major backthrust active during the Middle-Late Pleistocene bound the SW side of the Larissa high and can be straightly traced to join the Satanasso shear zone to the west (Fig. 1). To the south, the backthrusts bounding the Luana High can be merged on-land with the Civita shear zone along the southern side of the Pollino range. Other transpressional systems found offshore north of the Amendolara ridge can be laterally correlated with the Saraceno and Valsinni shear zones, the latter one having north-directed displacement (Fig. 1). The offshore faults appear arranged in arrays up to 80-100 km long, but individual segments have no more than 15 km length. Careful mapping of offset reflectors indicate that the offshore Civita fault zone slipped at ~0.5 mm/yr during the Early Pleistocene, but was less active afterwards. Conversely, the offshore Satanasso shear zone slipped at ~0.2- 0.3 mm/yr even during recent times; similarly, recent activity is found along the offshore Valsinni shear zone to the north at ~1.5 mm/yr. Slumping or creeping at more surficial levels occurs above listric normal faults localized on the steeper flanks of the Amendolara and frontal ridges. Marker correlation suggests that the listric faults are rooted within the Lower Pleistocene clays at depths no higher of 1.5 km. These sit- uations are similar to the tilted struc- Fig. 2 – Seismicity map of the study area (modified after Ferranti et al., 2009).

167 GNGTS 2009 SESSIONE 1.2 tural panels found on-land, indicating a shallow-crustal origin for these faults (Ferranti et al., 2009). Recent low to moderate magnitude crustal events were used to highlight the contemporary deformation pattern. For this analysis, we rely on a set of 2005-2007 focal mechanisms (3.0≤Ml≤4.0) calculated by Mucciarelli (2007), supplemented by Regional CMT fault-plane solutions (4.0≤Ml≤4.7) retrieved from the Mednet catalogue. The most energetic shocks concentrate along the coast and in the near offshore. Seaward of the Sibari plain, a mixture of thrust and strike-slip earthquakes are aligned with the ABFZ along the southern flank of the Amendolara ridge (Fig. 2). A second belt of thrust and strike-slip focal solutions is found to the south at the NE flank of the Sila massif (Fig. 2). Both at the northern and southern seismic belts, the NW-SE nodal planes parallel the trend of bedrock structures, and are consistent with marine geophysical lineaments. The P axis of the incre- mental strain tensor trends almost consistently ~ENE-WSW for both thrust and strike-slip earthquakes, and indicates substantial thrusting and left-transpression on the NW-SE striking structures (Fig. 2). Most of the events are located within the upper crust sedimentary cover above ~15-25 km depth (Fig. 2). This depth is roughly set at the base of the underthrust Apulian foreland platform from the Amendolara ridge to the Sila coast. We suggest that the Early Pleistocene strike-slip faults emanate from underneath the Apulian foreland plate underlying the inactive thin-skinned accretionary wedge, and are being currently reactivated in a transpressional regime. These structures form at least two deep-seated oblique backthrust belts, each of them composed of individual strands of maximum length <15 km, placing lim- its on the maximum expected earthquake size. References Catalano S., Monaco C., Tortorici L., Tansi, C.; 1993: Pleistocene strike-slip tectonics in the Lucanian Apennine (Southern Italy). Tectonics, 12, 656-665. Cucci L., Cinti F.R.; 1998: Regional uplift and local tectonic deformation recorded by the Quaternary marine terraces on the Ionian coast of northern Calabria (southern Italy). Tectonophysics, 292, 67-83. Doglioni C., Merlini S., Cantarella G.; 1999: Foredeep geometries at the front of the Apennines in the Ionian Sea (central Mediterranean). Earth Planet. Sci. Lett. 168, 243-254. Del Ben A., Barnaba C., Toboga A.; 2007: Strike-slip systems as the main tectonic features in the Plio-Quaternary kinematics of the Calabrian Arc. Mar. Geophys. Res., DOI 10.1007/s11001-007-9041-6. Ferranti L., Santoro E. Mazzella M.E., Monaco C., Morelli D.; 2009: Active transpression in the northern Calabria Apennines, Southern Italy. Tectonophysics, doi:10.1016/j.tecto.2008.11.010 Santoro E., Mazzella M.E., Ferranti L., Randisi E., Napolitano E., Rittner S., Radtke U.; 2009: Raised coastal terraces along the Ionian Sea coast of northern Calabria, Italy, suggest space and time variability of tectonic uplift rates. Quaternary International, 206, 78-101. Van Dijk J.P., Bello M., Brancaleoni G.P., Cantarella G., Costa V., Frixa, A., Golfetto F., Merlini S., Riva M., Torricelli S., Toscano C., Zerilli A.; 2000: A regional structural model for the northern sector of the Calabrian Arc (southern Italy). Tectonophysics, 324, 267–320. Van Dijk J.P., Bello M., Brancaleoni G.P., Cantarella G., Costa V., Frixa, A., Golfetto F., Merlini S., Riva M., Torricelli S., Toscano C., Zerilli A.; 2000: A regional structural model for the northern sector of the Calabrian Arc (southern Italy). Tectonophysics, 324, 267–320.

DEFORMAZIONE INTER E POSTSISMICA DA DATI GPS DEL BACINO DELL’AQUILA A. Galvani 1, A. Esposito 1, G. Pietrantonio 1, A. R. Pisani 1, E. Serpelloni 1, M. Anzidei 1, R. Devoti 1, F. Riguzzi 1, V. Sepe, A. Massucci 1, S. Del Mese 2 1 Istituto Nazionale di Geofisica e Vulcanologia, Roma 2 Istituto Nazionale di Geofisica e Vulcanologia, Milano

A partire da Dicembre 2008 l’area dell’Aquila è stata interessata da una lunga sequenza sismica che è culminata con l’evento catastrofico del 6 aprile 2009 (Mw 6.3). Il bacino dell’Aquila rica- de nel settore dell’Appennino Centrale, riconducibile al dominio di piattaforma carbonatica laziale- abruzzese, che è caratterizzato dalla presenza di sistemi di faglie attive normali orientate NW – SE responsabili dell’attività sismica di questa regione (Capitignano, Monte Marine, Monte Pettino,

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Assergi, Campo Imperatore, Lucoli, Campo Felice Colle Cerasitto, media Valle dell’Aterno). Negli ultimi 20 anni la distribuzione della sismicità nell’Appennino abruzzese era, poco significativa rispetto a quella registrata per il settore Umbro – Marchigiano. Terremoti storici di elevata magnitudo hanno interessato l’area dell’Aquila nel 1461 (Mw 6.5) e nel 1703 (Mw 6.6). I meccanismi focali della sequenza sismica a partire dal main shock del 6 aprile e degli after shock con Mw>4, indicano un sistema di faglia di tipo distensivo NW-SE riconosciuto nella faglia di Paganica. L’evoluzione spazio-temporale della sequenza sismica indica inoltre una migrazione verso prima verso SE e poi verso NNW degli epicentri. Il campo di velocità e di deformazione intersismico dell’Appennino Centrale è stato stimato a partire dai dati delle campagne GPS effettuate dal 1999 al 2007 sui 131 vertici della rete geodetica non permanente Ca_GeoNet (Anzidei et al., 2003) Dopo il sisma del 6 aprile sono stati misurati nuovamente 42 vertici della rete CA_GeoNet ubicati sia in area epicentrale sia nelle zone più distanti. Per entrambe le soluzioni ottenute, inter e post sismica, i dati GPS della rete non permanente sono stati combinati con i quelli provenienti da alcune reti permanenti: IGS, RING (INGV), ASI, di alcune Università Italiane e dalla Regione Abruzzo. Le misure effettuate su cinque caposaldi della rete Ca_Geonet a partire dal 3 aprile 2009 e i dati delle stazioni permanenti hanno permesso di stimare con precisione lo spostamento cosismico e di vincolare al geometria della sorgente attraverso l’inversione dei dati geodetici (Anzidei et al., 2009). In questo lavoro vengono presentati i risultati del confronto del campo di velocità e di deformazione inter e post-simico. Bibliografia Anzidei M., Galvani A., Esposito A., Cristofoletti P., Pesci A., Baldi P., Casula G., Cenni N., Loddo F. and Serpelloni E. (2003): The Central Apennines Geodetic Network (CA-Geonet): description and preliminary results. In XXVIII European Geophysival Society General Assembly, Geophys. Res: Abstr:, Vol 5, abstr EAE03-A-05288. Anzidei, M., E. Boschi, V. Cannelli, R. Devoti, A. Esposito, A. Galvani, D. Melini, G. Pietrantonio, F. Riguzzi, V. Sepe, and E. Serpelloni (2009): Coseismic deformation of the destructive April 6, 2009 L’Aquila earthquake (central Italy) from GPS data, Geophys. Res. Lett., doi:10.1029/2009GL039145.

VINCOLI GEOLOGICO-STRUTTURALI PER UN MODELLO SISMOTETTONICO IN CONDIZIONI DI DEFORMAZIONE NON COASSIALE, NELL’AREA DEL TIRRENO MERIDIONALE-SICILIA SETTENTRIONALE G. Giunta1, A. Giorgianni2, S. Orioli1 1 Dipartimento di Geologia e Geodesia, Università di Palermo 2 Dipartimento di Scienze della Terra, Università di Camerino

L’attività sismica che caratterizza la Sicilia settentrionale e l’antistante off-shore tirrenico, è connessa con l’architettura della catena Maghrebide realizzata attraverso fasi tettoniche compressiona- li, estensionali e trascorrenti continue sin dall’Oligocene superiore. L’attuale assetto della catena è il risultato dell’attivazione di strutture fragili neotettoniche a carattere strike-, net- e dip- slip, sin- tetiche destre e antitetiche sinistre, rispettivamente orientate NO-SE fino a O-E e N-S fino a NE- SO, studiate nei settori emersi della catena dove sono osservabili dalla scala chilometrica a quella metrica, controllano la genesi e l’evoluzione di zone di restraining e di depressioni tettoniche riem- pite da sedimenti clastici, presenti sia lungo le aree costiere della Sicilia settentrionale, dove talvolta dislocano depositi post-pliocenici, che negli antistanti settori sommersi tirrenici. La ricostruzione dell’ordine sequenziale delle deformazioni risulta estremamente complessa dato che la maggior parte delle strutture presentano sovrapposizioni di indicatori cinematici con caratteri diversi, che denotano la loro differente attività nel tempo. Al sistema trascorrente si sovraimpongono, a partire dal Pleistocene, faglie estensionali net- e dip-slip ad immersione tirrenica che giocano un ruolo di accomodamento nell’ambito del sollevamento recente delle porzioni emerse della catena Maghrebide. La deformazione fragile che interessa l’area Tirreno meridionale-Sicilia settentrionale è stata definita analizzando dati strutturali acquisiti sul campo nelle aree emerse della catena, ed

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Fig. 1 - Rilocalizzazione degli epicentri (A) e ipocentri (B) dei terremoti avvenuti nel Tirreno Meridionale tra il 1981 e il 2005 (Giunta et al., 2008). interpretando per le aree off shore carte morfobatimetriche e geologiche del Tirreno meridionale, che tuttavia soffrono di una certa carenza di dati morfobatimentrici nei settori prossimi alla costa. Nonostante ciò, i dati così acquisiti evidenziano la continuità di alcuni segmenti di faglie dalle aree emerse a quelle sommerse, come per altro dimostrato da dati sismici; inoltre, le orientazioni delle principali famiglie di faglie, appaiono del tutto simili, a meno di una maggiore dispersione angola- re lungo alcune direzioni nel settore sommerso, confermando attraverso la possibilità di confronto delle strutture nei due settori la compatibilità della griglia di faglie riconosciuta in terra con quella interpretata in mare. Il pattern deformazionale neotettonico e recente, in parte sismicamente attivo e responsabile della sismicità superficiale dell’area sud-tirrenica, viene interpretato come l’effetto dell’evoluzione di una zona di taglio regionale a componente destrale orientata circa O-E, estesa dal cosiddetto “rift di Pantelleria” a circa la congiungente Ustica-Eolie nel Basso Tirreno (Boccaletti et al., 1990; Nigro, 1998; Renda et al., 2000; Giunta et al., 2008), attiva sin dal Pliocene superiore. La zona di taglio controlla l’evoluzione della cerniera tra la porzione emersa e quella sommersa delle Maghrebidi siciliane (Gueguen et al., 2002; Giunta et al., 2008), che corrisponde ad un assottiglia-

Fig. 2 - Carta sismotettonica della zone di cerniera tra il Tirreno Meridionale e la Sicilia settentrionale (A); Campo di stress attivo nella zona sud-tirrenica e relazioni geometriche tra le strutture che si attivano all’interno della zona di taglio destro (B). (Modif. da Giunta et al., 2008).

170 GNGTS 2009 SESSIONE 1.2 mento crostale interposto tra il bacino Tirrenico, caratterizzato da processi di oceanizzazione, e la porzione emersa della catena siciliana costituita da crosta continentale. L’ intensa attività sismica dell’area sud tirrenica è concentrata principalmente in due province ipocentrali (Fig. 1): una più profonda che interessa prevalentemente la Sicilia nord-orientale, verosimilmente riferibile ai processi di subduzione dello slab litosferico ionico al di sotto dell’Arco calabro, ed una più superficiale che rappresenta l’espressione della deformazione fragile a carico della catena Maghrebide (Gueguen et al., 2002; Giunta et al., 2008). I meccanismi focali relativi ad alcuni eventi principali nel basso Tirreno indicano spesso una cinematica transpressiva e/o inversa su piani nodali orientati NE-SO, e talora transtensiva specie su piani nodali NO-SE, che sembrano confermare la compatibilità delle strutture sismogeniche con il modello tettonico regionale (Giunta et al; 2008). Negli ultimi anni sono state condotte, numerose ricerche multidisciplinari, sia a scala nazionale che a scala regionale, finalizzate alla elaborazione di carte di zonazione sismogenetica, vincolate a dati geologico- strutturali e geologico-geofisici, che hanno consentito, relativamente all’area in oggetto, l’elaborazione di modelli sismotettonici, non sempre congruenti tra loro, (Neri et al., 2008; Guarnieri, 2005; Pepe et al., 2003; Billi et al. 2006; Ferranti et al., 2008; Lavecchia et al., 2007, Giunta et al., 2008). La complessità dei processi sismogenici richiede che i modelli descrittivi siano basati su un eleva- to numero di informazioni sperimentali, riguardanti una consistente quantità di eventi e di strutture nell’ambito dei principali volumi sismogenici dell’area in studio. La comprensione del quadro sismotettonico dell’area in esame, sulla base della caratterizzazione delle faglie neotettoniche e l’individuazione di segmenti sismogenici tra quelle attive, risulta a tutt’oggi ancora notevolmente dif- ficoltosa dal momento che molto ancora rimane da comprendere sull’evoluzione dell’attività sismica in relazione alle strutture che generano i singoli eventi, sulla geometria e dimensione delle stes- se faglie attive, sulla loro eventuale prosecuzione in superficie, e sulla reologia dei volumi rocciosi che le contengono. Il presente lavoro rappresenta un tentativo di affrontare la problematica, nella zona Tirreno meridionale-Sicilia settentrionale, utilizzando un approccio inusuale. Attraverso l’analisi dei modelli sismotettonici esistenti per l’area oggetto di studio, sono state definite le macroaree sismogeniche, nell’ambito delle quali, l’analisi statistica dei dati sismologici disponibili consente di individuare i volumi sismogenici maggiormente attivi negli ultimi 25 anni. I numerosi dati sismologici esistenti hanno consentito altresì di focalizzare l’attenzione sulle strutture tettoniche che si sarebbero attivate nell’ambito dei volumi sismogenici. Al fine di vincolare maggiormente un modello sismotettonico proposto con dati geologico- strutturali, viene tentato un confronto tra il pattern strutturale neotettonico studiato in dettaglio in alcune aree emerse, che però non sono caratterizzate da attività sismica storica, con quello di aree sommerse sismicamente attive, ma dove l’assetto strutturale è stato ricostruito attraverso interpretazione di carte morfo-batimetriche e tettoniche. I dati sismologici e strutturali analizzati sembrano essere compatibili con un modello neotettonico, caratterizzato da una zona di simple shear, correlata ad un campo medio di stress, caratterizzato da un’asse di massima compressione (σ1) orientato circa NO-SE, il quale produce una complessa deformazione non-coassiale, con progressiva rotazione oraria dell’ellissoide delle deformazioni sia nel settore emerso della Sicilia che probabilmente in quelli sommersi del Basso Tirreno (Fig. 2). In particolari aree sono tuttavia possibili differenti condizioni sismogeniche, dovute all’accomodamento locale di volumi rocciosi in un contesto di marcata eterogeneità meccanica. Bibliografia Billi A., Barberi G., Faccenna C., Neri G., Pepe F., Sulli A.; 2006: Tectonics and seismicity of the Tindari Fault System, southern Italy: Crustal deformations at the transition between ongoing contractional and extensional domains located above the edge of a subducting slab. Tectonics, vol. 25, TC2006, doi:10.1029/2004TC001763. Boccaletti M., Nicolich R., Tortorici L.; 1990 : New data and hypothesis on the development of the Tyrrhenian Basin. Paleogeo. Paleoclim. Paleoecol., 77, 15-40. Ferranti L., Oldow J.S., D’Argenio B., Catalano R., Lewis D., Marsella E., Avellone G., Maschio L., Pappone G., Pepe F., and Sulli A.; 2008: Active deformation in Southern Italy, Sicily and southern Sardinia from GPS velocities of the Pery-Thirrhenian Geodetic Array (PTGA). Bollettino Società Geolgica Italiana, 127, (2), 229-316. Lavecchia G., Ferrarini F., De Nardis R., Visini F., Barbano M.S.; 2007: Active thrusting as possible seismogenic source in Sicily (Southern Italy): some insights from integrated structural-kinematic and seismological data. Tectonophysics 445, 145–167.

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Giunta G., Luzio D., Agosta F., Calò M., Di Trapani F., Giorgianni A., Oliveri E., Orioli S., Perniciaro M., Vitale M., Chiodi M., Adelfio G.; 2008: An integrated approach to the relationships between tectonics and seismicity in northern Sicily and southern Tyrrhenian, in stampa. Guarnieri P.; 2005: Plio-Quaternary segmentation of the south Tyrrhenian forearc basin. Int J Earth Sci (Geol Rundsch) DOI 10.1007/s00531-005-0005-2. Gueguen E., Tavarnelli E., Renda P., Tramutoli M.; 2002: The geodynamics of the southern Tyrrhenian Sea margin as revealed by integrated geological, geophysical and geodetic data. Bollettino Società Geologica Italiana, sp. vol. (1), 77-85. Neri G., Orecchio B., Presti D.; 2008: Sismicità attuale, campo di sforzo e dinamiche litosferiche nell’area della Stretto di Messina. Geoitalia, 25, 24-26. Nigro F.; 1998: Neotectonic events and kinematic of rhegmatic-like basins in Sicily and adjacent areas. Implications for a structural model of the Tyrrhenian opening. Ann. Soc. Geol. Poloniae, 68, 1-21. Pepe F., Sulli A., Agate M., Di Maio,D., Kok A., Lo Iacono C., Catalano R.; 2003: Plio-Pleistocene geological evolution of the northern Sicily continental margin (southern Tyrrhenian Sea): new insights from high resolution, multi-electrode sparker profiles. Geo-Marine Letters 23, 53–63. Renda P., Tavarnelli E., Tramutoli M., Gueguen E.; 2000: Neogene deformations of Northern Sicily, and their implications for the geodynamics of the Southern Tyrrhenian Sea margin. Memorie Società Geologica Italiana, 55, 53-59.

MONSOON SPEEDS UP INDIAN PLATE MOTION G. Iaffaldano1, L. Husson2,3, H.-P. Bunge4 1 Dept. of Earth and Planetary Sciences, Harvard University, Cambridge U.S.A. 2 CNRS Geosciences Renes, France 3 CNRS Universite de Nantes, France 4 Dept. of Earth and Environmental Sciences, LMU Munich, Germany A striking property of plate tectonics are short-term plate motion variations, on the order of a few Myrs. Such variations are a powerful probe into the nature of plate boundary forces, as mantle related buoyancy forces evolve on longer time-scales. Here we take a recent change of Indian plate motion and relate it directly to increased erosion and lowered elevation of the eastern Himalayas following recent monsoon intensification. We superimposing contributions of mountain building and erosion to arrive at a simple estimate of elevation change along the eastern Himalayan front. We show with global geodynamic simulations of the coupled mantle/lithosphere system that the estimate is consistent with the history of Indian plate kinematics for the past 10 Myrs. Our calcula- tions suggests that increased erosion of the eastern Himalayas acted to decrease its gravitational potential energy and its ability to resist convergence of the Indian plate towards Eurasia, allowing faster plate velocities along the eastern edge of the convergent margin and resulting ultimately in a rigid counter-clockwise rotation of India about a pole located north of the Carlsberg ridge. We find less agreement between modelled and observed plate motion if we assume a larger Indo-Australian plate, supporting the notion that India and Australia were separate tectonic units prior to monsoon intensification. To our best knowledge, this is the first quantitative evidence that climate acts as a force on large-scale plate motions, and represents a crucial advance in our understanding of how plates move.

AN ALTERNATIVE INTERPRETATION FOR THE SEISMIC SEQUENCE OF THE L’AQUILA EARTHQUAKE: A COMBINATION BETWEEN IMPOSED STRIKE-SLIP SYSTEM AND STRAIN ELLIPSE FRAME R.K. Kraus1, F.M. Elter1, C. Eva1, E. Eva 2, M. Padovano1, S. Solarino2 1 Dip.Te.Ris., Università di Genova, Genova 2 Istituto Nazionale di Geofisica e Vulcanologia, CNT, c/o Dip.Te.Ris., Genova The main shock of the l’Aquila seismic sequence occurred at 01:32 GMT of April 6 and was rated Mw=6.3. It occurred on a normal fault dipping SW of an angle between 45° and 54° at a depth

172 GNGTS 2009 SESSIONE 1.2 ranging from 8 to 10 km; the average slip of the fault was estimated to be 0.5 m. The earthquake was followed by some 20000 aftershocks, but the seismic activity is ongoing and the number of counts is of course still growing. The most important aftershocks were the Ml=5.3 of April 7 and the Ml=5.1 event of April 9. These two earthquakes occurred respectively southern and northern with respect to the main shock. The focal mechanisms relative to the earthquakes of 6- 9 April 2009 define an extension towards NE. Small arrangements, due to the daily addition of novel data and the completion of research studies, have been made on the focal parameters of the main and after shocks, but basically the whole scientific community nowadays agrees on the Fig. 1 - UM: Umbria-Marche Unit; SMU: Sannio-Molise Unit; SM: Sicily main characteristics of the Unit; PPF: Pliocene-Pleistocene Foreland; MM: Maiella Massif. episode and a few models have already been proposed for its occurrence. In this contribution we introduce an alternative model capable of either explaining the seismological evidences and to take into account the studies made by several authors which carried out on the likely causes for extension towards NE. Extension towards NE could be related to a setting of coeval different faults: 1. normal faults oriented NW-SE (Favali et al., 1993, Cello et al., 1997, Martini et al., 2001); 2. imposed sinistral stike-slip shear zones oriented NNW-SSE (persistent structural barriers as introduced by Pizzi and Galadini, 2009 for the Ancona-Anzio Line and Roccamonfina-Ortona Line); 3. R- synthetic strike-slip faults oriented NW-SE (see the geological map of Vezzani et al., 2009 and the models of Favali et al., 1993, Cello et al., 1997, Martini et al., 2001); 4. R’- antithetic oblique dextral strike-slip faults oriented WNW-ESE coeval with the NW-SE, R- synthetic strike-slip faults. One of these oblique dextral strike-slip faults could be represented by the Gran Sasso Line (previously interpreted just as a thrust fault), as already shown in the model suggested by Speranza et al. (2003); Many of these faults (imposed, R, R’ shear zones) are not linear and show a “snake” geometry. This particular fault-morphology is recognizable also at a smaller scale, as shown by the EMER- GEO Working Group (2009) when mapping the metric and decametric faults occurred during the April 6th, 2009 main shock in different manufacts. The “snake” geometry of faults is also suggested by the earthquake distribution in the L’Aquila area. The “snake” morphology of the faults cause the coeval presence of NW-SE releasing and NW-SE restraining bends: all these tectonic structures

173 GNGTS 2009 SESSIONE 1.2 are in agreement with the extension towards NE. The releasing bands are represented by the NW- SE pull-apart basin of Avezzano (Martini et al., 2001) and by the NW-SE L’Aquila-Sulmona basin. The restraining bands could be represented by the presence of pop-up structures such as the Maiella Massif (MM hereinafter). The interpretation of the Maiella Massif as a pop-up structure derive from many geological-morphological evidences, such as: a) the north–south, half-dome shape (Di Luzio et al., 2004); b) the presence at its border of the NNW-SSE Caramanico Fault; c) the marked asym- metry of the western and eastern slopes (this geomorphological setting is similar to those described by Gibbs (1989) in the Imperial Valley, California, in relation with a sinistral strike-slip); d) its sigmoidal shape comparable with the Restraining Analog Models proposed by McClay and Bonora (2001), related with two sinistral strike-slip shear zones. The Restraining Analog Model implies a lot of trasversal faults develop: similar transversal faults are mapped on the MM in the map by Vezzani et al. (2009). Secondary sigmoidal bodies and relative fault frame networks are recognizable also in the Sannio-Molise Unit (south of the MM) showing a good agreement with the model proposed by Mandl (1993). In relation to these data, we hypothesize that the geodynamic evolution of the L’Aquila area could be related to the action of regional imposed sinistral N-S strike-slip shear zones and their associated Riedel/strain ellipse (fig. 1). This geodynamic reconstruction seems to be in agreement with the coeval presence of restraining bends (such as the Maiella Massif) and releasing bends (such as the Fucino pull-apart). References Cello G., Mazzoli S., Tondi E., Turco E.; 1997: Active tectonics in the central Apennines and possible implications for seismic hazard analysis in peninsular Italy. Tectonophysics, 272, 43-68. Di Luzio E., Saroli M., Esposito C., Bianchi-Fasani G., Cavinato G.P., Scarascia-Mugnozza G.; 2004: Influence of structural framework on mountain slope deformation in the Maiella anticline (Central Apennines, Italy). Geomorphology, 60, 417–432. EMERGEO Working Group (in collaborazione con CNRIGAG,DiMSAT e Università degli Studi Roma TRE); 2009: Rilievi geologici nell’area epicentrale della sequenza sismica dell’Aquilano del 6 aprile 2009 (con appendice fotografica). Quaderni di Geofisica, http://portale.ingv.it/produzionescientifica/quaderni-di-geofisica/, 53 pp. Favali P., Funiciello R., Mattietti G., Mele G., Salvini F.; 1993: An active margin across the Adriatic Sea (central Mediterranean Sea). Tectonophysics, 219, 109-117. Gibbs A.D.; 1989: Structural styles in basin formation. In: Tankard A.J. & Balkwill, H.R. (eds), Extensional Tectonics and Stratigraphy of the North Atlantic Margins, AAPG Memoir, 46, 81-93. Mandl G.; 1993: Mechanics of Tectonic Faulting, Models and Basic Concepts. In Series Editor: H.J. Zwart, Developments in Structural Geology, 1, 1-407. Martini P. I., Sagri M., Colella A.; 2001: Neogene-Quaternary basins of the inner Apennines and Calabrian arc. In: Vai G.B., Martini P. I. (eds), Anatomy of an Orogen: the Apennines and Adjacent Mediterranean Basins, Kluwer Academic publisher, 375-400. McClay K., Bonora M.; 2001: Analog models of restraining stopovers in strike-slip systems. AAPG Bulletin, 85, 233-260. Pizzi A., Galadini F.; 2009: Pre-existing cross-structures and active fault segmentation in the northern-central Apennines (Italy). Tectonophysics, doi:10.1016/j.tecto.2009.03.018. Speranza F., Adamoli L., Maniscalco R., Florindo F.; 2003: Genesis and evolution of a curved mountain front: paleomagnetic and geological evidence from the Gran Sasso range (central Apennines, Italy). Tectonophysics 362, 183– 197 Vezzani L., Festa A., Ghisetti F.; 2009: Geological-structural map of the Central-Southern Apennines (Italy). Sheet 1 and 2, 1:250.000.

DIECI ANNI DI MISURE DI DEFORMAZIONE A PRATO CARNICO (UD) C. Marchesini 1, A. Vianello 2, G. Zambon 2 1 Dipartimento di Georisorse e Territorio, Università di Udine 2 CNR – Istituto di Scienze Marine, Venezia

Nell’abitato di Prato Carnico (UD), Alpi Carniche centrali, è in atto una frana lenta che riguar- da la parte centrale dell’abitato che si estende su due conoidi fortemente coalescenti formati da due piccoli torrenti affluenti di sinistra del Torrente Pesarina. a monte ed a valle di un tratto dalla SR 465, della Val Pesarina. Nel convegno GNGTS 2002 è già stata presentata una relazione su questo

174 GNGTS 2009 SESSIONE 1.2 problema, a cui si rimanda per l’introduzione geologica. Nell’agosto 1998, su consiglio del prof. Manzoni (Università di Trieste) e con la collaborazione del Comune di Prato Carnico, è stata pre- disposta una linea di livellazione lungo la citata Strada Regionale, che attraversa tutto il centro abitato. Sono stati installati 9 capisaldi (3 dei quali sono andati distrutti nel corso degli anni), costituti da bulloni inseriti verticalmente e cementati in strutture ritenute ben ancorate al suolo. La linea realizzata è lunga complessivamente 1 km; in essa, i capisaldi 4 e 5 si trovano nella zona compresa fra i due torrenti, mentre i capisaldi 3 e 6 sono posizionati in loro corrispondenza. Immediatamente dopo l’infissione dei capisaldi è stata eseguita la prima misura; successivamente, in genere nel mese di ottobre, è stata eseguita annualmente una una serie di livellazioni di alta precisione. Nell’ 2000 e nel periodo 2005 – 2007 sono state intensificate le misure, ripetendole ogni tre mesi. Ad ogni rilie- vo, tutti i dislivelli sono stati misurati in andata e ritorno, con autolivelli di precisione a lettura elet- tronica e stadie in invar; e gli errori di misura sistematici sono sempre risultati inferiori ad 1 mm. Nel 2000 è stata installata una seconda linea, passante all’interno del paese, connessa in due punti (collegamento ad anello) alla precedente. Nel 2005 e negli anni seguenti le linee sono state raffitti- te aggiungendo altri capisaldi, sia su manufatti al suolo che alla base degli edifici.

Fig. 1 – Rete di livellazione geometrica nell’abitato di Prato Carnico (UD).

Considerando solo i contrassegni che è stato possibile quotare ininterrottamente nel decennio di studio, dai risultati di tutte le misure risulta evidente che i capisaldi 4 e 5 si abbassano rispetto a tutti gli altri di quantità nettamente superiori agli errori di misura. Gli spostamenti degli altri contrassegni sono inferiori all’errore di misura e quindi non significativi. Siccome non ci sono riferimenti esterni, ossia non c’è una linea di livellazione nazionale a Prato Carnico, come zero di riferimento è stata scelta la media delle quote attribuite ai capisaldi 1, 3, 6, 7 e 9, i cui movimenti non sono significativi. Nella Fig. 2 vengono indicati gli spostamenti nel tempo (velocità) dei singoli capisaldi. Dal trend di movimento pertinente ad ogni contrassegno, per il 4 e 5 è evidente che l’abbassamento è abbastanza costante nel tempo. Nell’ultimo periodo si nota un rallentamento della velocità del caposaldo 4, che inizia dopo i lavori di rifacimento e stabilizzazione della strada SR465, eseguiti nel 2007. La linea del caposaldo 5 si interrompe prima delle altre, in quanto esso è andato distrutto in conseguenza dei sopracitati lavori. Nella Fig. 3 sono rappresentati gli spostamenti nel tempo (velocità) dei nuovi capisaldi installati lungo il sentiero ai piedi del conoide che viene inciso fino al substrato dal Torrente Pesarina. Gli spostamenti misurati risultano maggiori di quelli verificati lungo l’asse viario soprastante. L’improvvisa variazione di velocità di abbassamento registrata nel 2007 in corrispondenza dei capisaldi 207 e 208 è imputabile ai citati lavori. Il caposaldo 106 si trova al di fuori della zona interes-

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Fig. 2 – Variazioni di quota nel tempo dal’inizio delle misure lungo la SR465. sata al movimento. Se si calcolano le velocità dei movimenti verticali si nota un aumento genera- lizzato in corrispondenza dei lavori del 2007, poi tutte le velocità si sono stabilizzate. Sul lato a monte della strada le velocità sono comprese fra -4 e -6 mm/anno, mentre solo il cs 4 raggiunge –8 mm/anno; sul lato a valle, le velocità variano fra -4 e –11 mm/anno, ma due cs sul sentiero sotto- stante la strada raggiungono la velocità di –16 mm/anno.

Fig. 3 – Variazioni di quota nel tempo dei nuovi capisaldi sotto la strada.

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Ringraziamenti. Si ringrazia per l’impegno profuso e la professionalità dimostrata in molti anni di rilievi di campagna il seguente personale del CNR: Giancarlo Arcari, Nicola Cavallarin, Giancarlo Dal Missier, Loris Dametto, nonchè i laureandi: Franco Bisaro, Leonardo Regazzo, Monica Trapani. Le misure nel periodo 2005 – 2007 sono state finanziate mediante un contratto con la Protezione Civile del Friuli-Venezia Giulia.

UPPER AND LOWER CRUSTAL EVOLUTION DURING LITHOSPHERIC EXTENSION: NUMERICAL MODELLING AND NATURAL FOOTPRINTS FROM THE EUROPEAN ALPS A.M. Marotta1, M.I. Spalla2, G. Gosso2 1 Sezione di Geofisica, Università degli Studi di Milano, Dipartimento di Scienze della Terra “A. Desio”, Milano 2 Sezione di Geologia e CNR-IDPA, Università degli Studi di Milano, Dipartimento di Scienze della Terra “A. Desio”, Milano

Igneous and metamorphic records, as well as structural and sedimentary imprints of rifting-related lithospheric extension, are frequently ambiguous. This is the case with high-temperature–low- pressure (HT–LP) metamorphism, which is undoubtedly related to high thermal regimes and can be consequent to the late orogenic collapse of a collisional belt or to the lithospheric thinning, thereby promoting continental rifting (e.g. Thompson 1981; Wickham & Oxburgh 1985; Sandiford & Powell 1986; Platt 1998; Beardsmore & Cull 2001). The same uncertainty holds for the normal faulting that can accommodate the lateral expansion of the thickened axial part of a mountain belt during the final stages of continental collision, when gravitational forces dominate the horizontal stress field or, alternatively, accommodate lithospheric thinning in the axial zone of continental rifting (e.g. Wernicke 1985; Molnar & Lyon-Caen 1988; Keen et al. 1989; Malavieille 1993; Vissers et al. 1995). This interpretative ambiguity is enhanced when continental rifting does not develop on a stable continental lithosphere, but follows the thermal and mechanical instabilities induced by a subduction–collision process in which the rifting precursor signals overprint the markers of a late orogenic extension. This latter case corresponds to that of the European Alps, where the exposure of Variscan structures and metamorphic imprints within the present-day Alpine structural domains indicates that before the Pangaea break-up the continental lithosphere was thermally and mechani- cally perturbed by Variscan subduction and collision. The overprint of HT Permian–Triassic evolution on the HP relics of the Variscan subduction and collision has been interpreted as induced either by late-orogenic collapse or by lithospheric extension and thinning leading to continental rifting (e.g. Lardeaux & Spalla 1991; Diella et al. 1992; Gardien et al. 1994; Ledru et al. 2001). Even the interpretation of the geodynamic environment responsible for the development of intracontinental basins hosting the Permian volcanic products allows of two possible alternatives, one envisaging a strike-slip dominated regime (Arthaud & Matte 1977; Cassinis & Perotti 1994), which is compatible with the evolution of a mature collisional setting (Molnar & Lyon-Caen 1988), the other a continental rifting tectonic setting (Siletto et al. 1993; Selli 1998; Staehle et al. 2001). In both cases the continental rifting promoting Mesozoic opening of the ocean in a lithosphere thermally softened and thinned by slab break-off processes is generally accomplished in the final stages of continental collision. Trying to resolve the dualistic interpretation of the geodynamic significance of the Permian–Triassic high thermal regime, Marotta & Spalla (2007) and Spalla & Marotta (2007) used numerical models to simulate ocean subduction leading to continental collision, lithospheric detachment and subsequent gravitational thermal relaxation. Comparing model predictions with natural data, they concluded that the Permian–Triassic metamorphic and igneous imprints in the Alps cannot simply result from the thermal relaxation consequent to lithospheric unrooting during late orogenic extension, and that a supplementary mechanism, such as hot mantle upwelling under continental plates, was necessary to satisfy the Permian–Triassic geothermal state required to account for the natural tectono-metamorphic data. Indeed, the lithospheric thermal detachment was premature

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(360 Ma) with respect to natural thermal signals (290–225 Ma). In the present work we expand the analysis by Marotta & Spalla (2007) on the effects of a forced extension during the Permian–Triassic period (from 300 to 220 Ma) via new models characterized by extension velocities varying from no extension to 2.0 cm a-1. To understand the geodynamic settings at the Permian–Triassic high thermal regime, we use finite-element techniques to model the active lithospheric extension process overprinting the deformation patterns driven by a previous phase of oceanic subduction, followed by continental collision and purely gravitational evolution. The continuity, momentum and energy equations are integrated within a rectangular domain in which the flow is driven by velocity boundary conditions and density contrasts. The 2D finite-element code SubMar (Marotta et al. 2006) is used for the analysis, which accounts for a crust compositionally differentiated from the mantle via the Lagrangian particle technique (e.g. Christensen 1992), as in Marotta & Spalla (2007) and an incompressible viscous fluid with temperature and composition-dominated viscosity and density. The initial configuration of the four models corresponds to the shallow and deep heterogeneities generated at 300 Ma by an oceanic subduction, which consumed a 2500 km wide ocean during a 52.5 Ma convergence from 425 to 372.5 Ma (e.g. Tait et al. 1997; von Raumer et al. 2003), followed by continental collision and a purely gravitational evolution for 72.5 Ma, thereby reproducing the Variscan subduction and collisional phases affecting the pre- Alpine continental crust (Marotta & Spalla 2007; Spalla & Marotta 2007). In order to account for this previous history, we use as initial distributions of temperature and crustal markers those corresponding to the geodynamic setting at 300 Ma after simulation of Variscan subduction–collision in Marotta & Spalla (2007). Model predictions of lithospheric thermal state and strain localization are compared with metamorphic data, time interval of plutonic and volcanic activity and coeval onset of sedimentary envi- ronments. Our analysis demonstrates that the integrated use of geological data (metamorphic PT estimates, magmatic and sedimentary histories) and predictions of numerical modelling, which take into account the thermal instabilities induced by mechanic perturbations, sheds light on the tectonic evolution of a fossil passive margin dispersed in separate fragments within a subduction–collisional belt, as is the case for the Permian–Triassic thinned continental lithosphere recycled in the Alpine orogen. In the specific case of the European Alps, a relative high rate of active extension is required, associated for example with a far extensional field, to achieve the fit with the maximal number of tectonic units. Furthermore, thermal conditions allowing partial melting of the crust accompanying gabbroic intrusions and HT–LP metamorphism are generated. The concordant set of geologic events that took place from Permian to Triassic times in the natural Alpine case is justified by the model and is coherent with the progression of lithospheric thinning, later evolving into the generation of an oceanic lithosphere. On a large scale, uprising of previously subducted crust occurs mainly underneath the upper continental plate, reaching shallower depth for the higher extensional model, and underplating takes place over a wider area below the thinned crust. Crustal thinning is proportional to the assumed extensional velocity and ranges from almost 0, for a purely gravitational evolution, to c. 80%, when the maximum rate of extension is 2.0 cm a-1. In the purely gravitational model, decoupling of the deformation regime occurs between the upper crust and the lower crust/mantle coherent system, whereas in the active extensional models the extensional regime is widespread through the crust, allowing strain rate localization that in the natural systems may correspond to faulting that generates basin opening and provides magma ascent pathways from deep seated mafic and acidic intrusions. Strain localization shows a periodicity comparable per order of magnitude with episodic faulting and related volcanic pulses, periodic basin deepening and facies fluctuations in natural systems. In the active extensional models, a low extension velocity of 0.5 cm a-1 reduces the minimal P/T ratio to a half with respect to that of the purely gravitational model. However, crustal thinning is not accompanied by a concurrent thermal erosion and, hence, the thermal state of the crust remains rather low to satisfy completely the PT values frozen in Permian–Triassic mineral assemblages. Only at a rate of forced extension of 2.0 cm a-1 does the data

178 GNGTS 2009 SESSIONE 1.2 set from the Southalpine domain begin to fit and the maximal number of tectonic units from all structural domains are matched by the predicted thermal regime. Only this last model generates thermal conditions suited to a partial melting of the crust accompanying mafic magma emplacement and HT–LP metamorphism. Our model is physically compatible with the natural case in which the distribution of gabbro complexes in the Austroalpine and Southalpine crusts suggests that the rifting was asymmetrical and that the continental crust belonging to these two domains acted as a hang- ing wall during an asymmetric lithospheric thinning that paved the way to the opening of the western Tethys ocean. This interpretation is supported in the natural Alpine case by the gradual age transition between the Permian–Triassic magmatic and metamorphic histories that ends with ocean crust formation; this picture is reinforced by a comparison with the new Permian ages obtained from gabbros and tonalites underplating the thinned continental crust of the present-day passive Galicia margin. References Arthaud, F. & Matte, P.; 1977: Late Paleozoic strikeslip faulting in southern Europe and northern Africa: result of a right-lateral shear zone between the Appalachians and the Urals. Geological Society of America Bulletin, 88, 1305–1320. Beardsmore, G. R. & Cull, J. P.; 2001: Crustal heat flow. Cambridge University Press, London. Cassinis, G. & Perotti, C.; 1994: Interazione strutturale permiana tra la linea delle Giudicarie ed i bacini di Collio, Tione e Tregiovo (Sudalpino centrale, N Italia). Bollettino della Societa Geologia Italiana, 112, 1021–1036. Christensen, U. R.; 1992: An Eulerian Tecnique for thermo-mechanical model of lithospheric extension. Journal of Geophysical Research, 97, 2015–2036. Diella, V., Spalla, M. I. & Tunesi, A.; 1992: Contrasted thermo-mechanical evolutions in the Southalpine metamorphic basement of the Orobic Alps (Central Alps, Italy). Journal of Metamorphic Geology, 10, 203–219. Gardien, V., Reusser, E. &Marquer, D.; 1994: Pre- Alpine metamorphic evolution of the gneisses from the Valpelline Series (Western Alps, Italy). Schweizerische Mineralogische und Petrographische Mitteilungen, 74, 489–502. Keen, C., Peddy, C., De Voogd, B. & Matthews, D.; 1989: Conjugate margins of Canada and Europe: results from deep reflection profiling. Geology, 17, 173–176. Lardeaux, J. M.&Spalla,M. I.; 1991: From granulites to eclogites in the Sesia zone (Italian Western Alps): a record of the opening and closure of the Piedmont ocean. Journal of Metamorphic Geology, 9, 35–59. Ledru, P. Et Al.; 2001: The Velay dome (French Massif Central): melt generation and granite emplacement during orogenic evolution. Tectonophysics, 332, 207–237. Malavieille, J.; 1993: Late orogenic extension in mountain belts: insights from the Basin and Range and the Late Paleozoic Variscan Belt. Tectonics, 12, 1115–1130. Marotta, A. M. & Spalla, M. I.; 2007: Permian– Triassic high thermal regime in the Alps: result of Late Variscan collapse or continental rifting? Validation by numerical modeling. Tectonics, 26, pTC4016, doi: 10.1029/2006TC002047. Marotta, A. M., Spelta, E. & Rizzetto, C.; 2006: Gravity signature of crustal subduction inferred from numerical modelling. Geophysical Journal International, 166, 923–938. Molnar, P. & Lyon-Caen, H.; 1988: Some simple physical aspects of the support, structure and evolution of mountain belts. In: EDITOR, A. (ed.) Volume title. Geological Society of America Special Papers, 218, 179–207. Platt, J. P.; 1998: Thermal evolution, rate of exhumation, and tectonic significance of metamorphic rocks from the floor of the Alboran extensional basin, western Mediterranean. Tectonics, 17, 671–689. Sandiford, M. & Powell, R.; 1986: Deep crustal metamorphism during crustal extension: modern and ancient examples. Earth and Planetary Science Letters, 79, 151–158. Selli, L.; 1998: Il lineamento della Valsugana fra Trento e Cima d’Asta: cinematica neogenica ed eredita` strutturali permo mesozoiche nel quadro evolutivo del Sudalpino orientale (NE Italia). Memorie della Societa` Geologia Italiana, 53, 503–541. Siletto, G. B., Spalla, M. I., Tunesi, A., Lardeaux, J. M. & Colombo, A.; 1993: Pre-Alpine structural and metamorphic histories in the Orobic Southern Alps, Italy. In: EDITOR, A. (ed.) Pre-Alpine basement in the Alps. Springer-Verlag, Heidelberg, 585–598. Spalla, M. I.&Marotta, A. M.; 2007: P–T evolutions vs. numerical modelling: a key to unravel the Paleozoic to early-Mesozoic tectonic evolution of the Alpine area. Per. Mineral., 76, 267–308. Staehle V., Frenzel G., Hess J. C., Saup F., Schmidt S.T. & Schneider W.; 1990: Zircon syenite pegmatites in the Finero peridotite (Ivrea zone): evidence for a syenite from a mantle source. Earth and Planetary Science Letters, 101, 196–205. Tait, J. A., Bachtadse, V., Franke, W. & Soffel, H. C.; 1997: Geodynamic evolution of the European Variscan fold belt: paleomagnetic and geological constraints. Geologisches Rundschau, 86, 585–598. Thompson, A. B.; 1981: The pressure–temperature (P,T) plane viewed by geophysicists and petrologists. Terra Cognita, 1, 11–20. Vissers, R. L. M., Platt, J. P. & Van Der Wal, D.; 1995: Late orogenic extension of the Betic Cordillera and Alboran Domain: a lithospheric view. Tectonics, 14, 786–803. Von Raumer, J., Stampfli, G. & Bussy, F.; 2003: Gondwana-derived microcontinents – the constituents of the Variscan and Alpine collisional orogen. Tectonophysics, 365, 7–22. Wernicke, B.; 1985: Uniform-sense normal simple shear of continental margins. Canadian Journal of Earth Sciences, 22. Wickham, S. M. & Oxburgh, E. R.; 1985: Continental rifts as a setting for regional metamorphism. Nature, 318, 330–333.

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HOW LITHOSPHERIC SUBDUCTION CHANGES ALONG THE CALABRIAN ARC IN SOUTHERN ITALY: GEOPHYSICAL EVIDENCES G. Neri 1,2, A.M. Marotta 3, B. Orecchio 4, D. Presti 1, C. Totaro 1, R. Barzaghi 5, A. Borghi 5 1 Department of Earth Sciences, University of Messina 2 Istituto Nazionale di Geofisica e Vulcanologia, Rome 3 Department of Earth Sciences, University of Milano 4 Department of Physics, University of Calabria, Arcavata di Rende (CS) 5 DIIAR, Department of Environmental, Hydraulic, Infrastructures and Surveying Engineering, Politecnico di Milano

A local earthquake tomography recently performed down to 300km depth in the Calabrian Arc region evidenced that the Ionian subducting slab is in-depth continuous beneath the central part of the Arc while detachment of the deep portion of the subducting structure already occurred beneath the edges of the Arc itself. In the present study, seismic tomography at shallow depth furnishes evidence of SE-ward migration of the Tyrrhenian crust in the Calabrian area and the migration front is found to finely correspond to the portion of the Arc where the subducting slab was found continuous and trench retreat can be presumed to have been active in the most recent times. Clear support to this geodynamic view is given by surface gravity anomalies which evidence deep structure het- erogeneity along the Arc closely matching with the lithospheric subduction changes (continuous vs detached subducted slab) detected by seismic tomography. Good location finds in this framework the space distribution of recent crustal seismicity which evidences NW-trending seismogenic structures in northeastern Sicily and northern Calabria interpretable as shear zones accommodating the southern Tyrrhenian SE-ward kinematics. This view of the processes also incorporates the geostruc- tural data, specifically the NW-trending transtensional fault systems reported in the literature for Northeastern Sicily and Northern Calabria that we propose as seismogenic lateral boundaries of the SE-ward migrating Tyrrhenian lithosphere. Also, the analysis of recent crustal seismicity brought us to detect seismolineaments in southern Calabria corresponding to the NE-trending longitudinal structures of the Arc where the great historical earthquakes of 28 December 1908, and 5 and 7 February 1783 occurred. Seismicity and the extensional stress regime detected in these structures may also represent a response to subduction slab rollback and trench retreat in the central part of the Arc (southern Calabria).

TOMOGRAPHIC IMAGING OF P- AND S- WAVE VELOCITY STRUCTURE BENEATH THE CALABRIAN ARC REGION (SOUTH ITALY): AN IMPROVED VIEW OF THE SUBDUCTION SYSTEM B. Orecchio 1, D. Presti 2, C. Totaro 2, I. Guerra 1, G. Neri 2,3 1 Department of Physics, University of Calabria, Arcavata di Rende (CS) 2 Department of Earth Sciences, University of Messina 3 Istituto Nazionale di Geofisica e Vulcanologia, Rome

A recently published tomographic investigation of the Calabrian Arc, South Italy (Neri et al., 2009) has shown that the Ionian subducting slab is in-depth continuous only beneath the central part of the Arc (southern Calabria), while it has already undergone detachment at the edges of the arcuate structure (northern Calabria and northeastern Sicily). In the present study we have developed a new 3D velocity model of the crust and upper lithosphere in the Calabrian Arc area using the method proposed by Waldhauser et al. (1998, 2002) and the seismic velocity data (DSS and WARR profiles, P- and S-wave tomographic studies, etc.) available for the study region. We merged this structure into an averaged regional velocity model, ranging between the surface and 300km depth, that we used to perform new P- and S-wave tomographic inversion of shallow and deep earthquakes occurred between 1975 and 2008. All the data available from the national and local networks,

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GNGTS 2009 SESSIONE 1.2 including the CAT-SCAN and UniCal network, have been used for inversion. The investigation allows us to propose an improved and more complete view of the subduction system with respect to the previous works, including Neri et al. (2009). References Neri G., Orecchio B., Totaro C., Falcone G., Presti D.; 2009: Subduction beneath southern Italy close the ending: results from seismic tomography. Seim. Res. Lett., 80, 63-70. Waldhauser F., Kissling E., Ansorge J., Mueller S.; 1998: Three-dimensional interface modelling with two-dimensional seismic data: the Alpine crust-mantle boundary. Geophys. J. Int., 135, 264-278. Waldhauser F., Lippitsch R., Kissling E., Ansorge J.; 2002: High-resolution teleseismic tomography of upper-mantle structure using an a priori three-dimensional crustal model. Geophys. J. Int., 150, 403–414.

NATURAL AND CONTROLLED SEISMIC EXPERIMENT ON THE PROFILE IN TRANSITION AREA FROM THE DINARIDES TO PANNONIAN BASIN J. Oresˇkovic´1, F. Sˇumanovac1, E. Hegedüs2, D. Dudjak1, A. C. Kovács2, S. Kolar1 1 University of Zagreb, Faculty of Mining, Geology and Petroleum Engineering, Zagreb, Croatia 2 Eötvös Loránd Geophysical Institute of Hungary, Budapest, Hungary

Introduction. The study area is related to the transition between the Dinarides and the Pannonian basin, as a contact between the Adriatic microplate and Pannonian segment. It is based on the results of active seismic experiment ALP 2002 and recent passive seismic project ALPASS- DIPS (Alpine Lithosphere and Upper Mantle PASsive Seismic Monitoring - DInarides-Pannonian Segment). Our analysis was carried out on profile Alp07, which is a part of the ALP 2002, a large international seismic refraction experiment that focused on the lithospheric structure of the Eastern Alps, the northwestern Dinarides, the eastern part of Pannonian basin and western part of the Bohemian massif (Brückl et al., 2007). Profile Alp07 stretches from Istra to the Drava River at Hungarian–Croatian border in a WSW-ENE direction (Fig. 1). It is oriented approximately perpendicular to the Dinarides, the main faults in the Adriatic region, and the contact between the Dinarides and Pannonian basin. The ALPASS-DIPS project followed successful active source

Fig. 1 - Locations of the temporary seismic stations and Alp07 profile on a tectonic map of the investigation area.

181 GNGTS 2009 SESSIONE 1.2 experiment, and its main objective is to apply passive seismic methodology in research of the lithosphere processes and structures. To reach this goal, temporary seismic stations were deployed along Alp07 profile (Fig. 1). Recorded seismic data have been interpreted by a Receiver Functions method, in order to determine Earth’s crust and upper mantle velocity discontinuities in the survey area. Seismic model. Seismic modelling, both inverse and forward, was performed on the data gath- ered along Alp07 profile, for the purpose of determining the structure of the lithosphere and relationships between the Adriatic microplate and the Pannonian basin of the Eurasian plate. The velocity model along Alp07 profile shows that the Moho depth is the greatest in the area of the Dinarides, reaching about 40 km and is shallowest (20–30 km) in the Pannonian basin area (Fig. 2). Three types of crust were defined along the profile: the Dinaridic and the Pannonian crusts that are separated by a relatively wide transition zone. The Dinaridic upper crust is characterized by low seismic velocities, but velocities in lower crust are high. The Pannonian crust can be seen as unique layer characterized by low seismic velocities. Large lateral and vertical changes in seismic velocities can be found in the transition zone (Fig. 2). Troughs in the seismic model at the level of the Mohorovicˇic´ discontinuity are interpreted as major faults in the lithosphere (Sˇumanovac et al., 2009).

Fig. 2 - Velocity model along Alp07 profile from the ALP 2002 experiment (Sˇumanovac et al., 2009).

Deployment and data analysis. Temporary seismic stations (12) were deployed on the profile Alp07 (Fig. 1). The stations consisted of 3-component short-period seismic sensors and data logger (ELGI-DAS). Seismic waves were continuously recorded with the frequency sample rate of 50, from November, 2005 to May, 2007. Teleseismic data have been used for P-receiver functions analysis. More than 70 events have been selected at epicentral distances between 30° and 90° with magnitude greater than 5.5. Number of selected earthquakes varied between 22 and 40 per station. Two of the stations had less number of events (18), due to lack of data or high noise level. Most of the events are from North-American/Pacific plate contact and they are visible at major number of stations. However, only a small number of events are from Atlantic Ocean and Africa. Earthquake distribution considering backazimuth is mainly in the I and II quadrant. The magnitude of earth-

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GNGTS 2009 SESSIONE 1.2 quakes ranged from 5.7 to 6.5. Number of visible earthquakes can be connected with depth and magnitude. Earthquakes with hypocenter between 10 and 60 km and magnitude over 6.5, have been recognized at major number of stations. Accordingly, earthquakes with hypocenter out of that range, and with magnitude less than 6.5, could be recognized at only a few stations. Receiver functions. The recorded data were processed using P-receiver function method (PRF). It is a method which is based on analysis of converted P-to-S phase (Langston, 1979). Teleseismic body waveforms recorded at seismic station contain information on the earthquake source, ray path and structure in the vicinity of both source and the receiver. The receiver functions are obtained by deconvolution, used to isolate the response of the structure below receiver from other influences. The component, obtained after deconvolution, is called the P-receiver function and contains mostly energy of converted Ps wave, and thus the information about the structure below seismic station. Arrival time of converted Ps phase on the receiver function component depends on the discontinuity depth. Receiver functions calculated for different events at each station are stacked. In this way, the signal-to-noise ratio is improved. To obtain constructive interference, it is required that receiver functions are equalized with respect to the ray parameter. Moveout correction of the ray path for all epicentral distances is done with respect to the arrival time of Ps conversion at a reference epicentral distance of 67° (ray parameter 6.4 sec/°). Results. P-receiver functions are calculated for all stations (Cro_01 to Cro_12) and for station CBP4M located in the northeastern extension of the profile. Stacked traces are displayed in Fig. 3. The arrival times of Ps conversions at Mohorovicˇic´ discontinuity are between 3.8 and 6.6 s. At the beginning of the profile the Ps phase can be observed at 5 s delay time. Under the Dinarides delay time increases up to 6.6 s. Ps conversion at Moho in the transition zone (stations Cro_06 to Cro_09) becomes shallower, with Ps time between 5.5 and 5 s (lower dashed line in Fig. 3). In this part there is also converted phase with strong amplitude between 2.8 and 4 s (upper dashed line in Fig. 3), which most probably originates from velocity discontinuity in the crust. Velocities in the upper crust under these stations are low (Fig. 2) and velocity contrast at the upper/lower crust boundary is strong. The minimum Moho Ps time is observed in the Pannonian part, in the range from 3.8 to 4.5

Fig. 3 – Stacked P-receiver functions along Alp07 profile.

183 GNGTS 2009 SESSIONE 1.2 s. In the transition zone and in the Pannonian basin, the first positive phase on the receiver functions is converted Ps phase from the shallow discontinuity. Therefore, under these stations the presence of a significant sedimentary layer can be observed between 0.4 and 1.0 s delay time. Results of the Moho depth obtained from migrated receiver functions and results of deep refraction experiment ALP 2002 generally agree under the Dinarides and in the Pannonian basin area. However, there are differences in the transition zone which can be observed under stations Cro_06 to Cro_09. Disagreement could be caused by velocity anomalies in the upper crust, and high velocity contrast between upper and lower crust in the transition zone. Geophysical model of Alp07 profile already implied that Adriatic microplate is subducting under the Pannonian segment. According to the results of receiver functions, the change in Moho depth occurs between stations Cro_05 and Cro_06, therefore the subduction is observed on the northeastern part of the Dinarides. Acknowledgements. The final data processing and interpretation was performed within the project ‘Geophysical explorations of water-bearing systems, environment and energy resources’, approved by the Ministry of Science, Education and Sports of the Republic of Croatia. References Brückl, E., Bleibinhaus, F., Gosar, A., Grad, M., Guterch, A., Hrubcová, P., Keller, G.R., Sˇumanovac, F., Tiira, T., Yliniemi, J., Hegedüs, E., Thybo, H.; 2007: Crustal structure due to collisional and escape tectonics in the Eastern Alps region based on profiles Alp01 and Alp02 from the ALP 2002 seismic experiment. J. Geophys. Res., 112, B06308, doi: 10.1029/2006JB004687. Langston, C.A.; 1979: Stucture under Mount Rainier, Washington, inferred from teleseismic body waves. J. Geophys. Res., 84, 4749-4762. Sˇumanovac, F., Oresˇkovic´, J., Grad, M. and ALP 2002 Working Group; 2009: Crustal structure at the contact of the Dinarides and Pannonian basin based on 2-D seismic and gravity interpretation of the Alp07 profile in the ALP 2002 experiment. Geophys. J. Int., 179, 615-633, doi: 10.1111/j.1365-246X.2009.04288.x.

SEQUENTIAL TECHNIQUE FOR JOINT INVERSION OF GRAVIMETRIC AND SEISMIC DATA APPLIED TO THE SICILIAN AREA S. Panepinto1, M. Calò1,2, C. Dorbath2, A. D’Alessandro3, G. D’Anna3, D. Luzio1 1 Dipartimento C.F.T.A. Università di Palermo 2 IRD-IPGS, Strasbourg 3 INGV, CNT, Roma

A procedure for the construction of 3D velocity-density models and earthquake relocation by integrated inversion of P and S wave traveltimes and Bouguer anomaly distribution was applied to a large data set concerning the Sicilian area and portions of the surrounding basins. In order to cut down the data and the number of model parameters, the seismic data set was subdivided into two subsets for separate inversions. The obtained results were later on joined by the WAM (Weighted Average Model) technique. This is a post-processing technique proposed by M. Calò et al. (2008) by which numerous tomographic models, relative to a same data set with different selection of a- priori inversion parameters as well as to different data set, are unified in a common 3D grid. The Fig. 1 shows the total investigated volume that was obtained through the merging of two WAM tomographic inversions relative to the two above cited subsets. The first data set concerns 28873 P and 9990 S arrival times of 1800 earthquakes located in the area 14°30’ E - 17°E, 37°N - 41°N while the second data set contains 31250 and 13588 S arrival-times related to 1951 events located in the area 11° E - 15°48’ E, 36°30’N - 39°N. The selected events were recorded at least by 10 stations in the period 1981-2005 and marked by RMS < 0.50 s. The second data set was integrated with P-wave traveltimes picked in seismic profiles relative to the high density W.A.R.R. and D.S.S. experiments carried out in the study region since the earlier 1970. The Bouguer anomaly data set contains values (gb) interpolated into the nodes of a 8x8 km regular grid covering the area 12° E - 16°01’ E, 37°30’ N - 38°31’ N.

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Fig. 1 - The picture shows the total investigated volume of the study area characterized with a DWS >100.

The applied procedure allows to integrate seismic and gravimetric data inversions with a sequential technique in order to avoid the problematic opti- mization of the relative weights to assign to the different type of data. In the following, the main steps of the procedure are summarized. Since the Vs model is often much less constrained by the experimental data than the Vp model, a first classic tomographic inversion provides just a preliminary Vp model and a first ipocentral relocation. The Vp model is then converted into a pseudo-Vs model, through a Vs-Vp correlation law (Eq. 2) proposed by Brocher (2005). This last one is used, jointly to the Vp model and to the first relocation results, as input for the first WAM inversion that provides the first Vp, Vs and Vp/Vs models and a new ipocentral relocation of the iteration cicle. The results previously obtained are used to derive two density distributions (ρp,ρs) associated to the Vp and Vs models respectively, by the empirical Brocher’s equations: (1)

(2)

These density models are statistically compared, in spatial and wave number domains, and the distribution of their average value is determined. In the previous formula σp and σs are the standard deviation distributions of ρp and ρs obtained, from Eq. 1 and 2, by using the simple propagation rule for normal distributed errors, and the Vp and Vs standard deviation distributions determined by the WAM topographic technique. Afterwards, two extreme density distributions are calculated using the following relation:

(3) where the k index depends on the selected confidence level used to define the uncertainty of the velocity distributions. In the equation 3 it doesn’t take into account typical dispersion of the empirical correlations ρ → Vp and ρ → Vs to force the constraining effect of the gravimetric data. The − max gravimetric effects of the mean density model (gc), maximum density model (gc ) and minimum min density model (gc ) have been calculated using the 3GRAINS code, implemented by Snopek and Casten (2006). The program uses the Nagy formula (1966) to calculate the gravity attraction of right rectangular prisms. In order to significantly reduce the border effects the 3GRAINS program by itself automatically extends the edge blocks into ‘‘infinity’’. It has been attributed to these blocks density values that take into account the real trend of the main lithospheric structures in a surrounding zone about 300 km wide. The Figs. 2 and 3 clearly suggest the necessity to correct this initial density model. Probably, these corrections will not be consistent with the trend and the dispersion of the aforesaid empirical correlations.

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Fig. 2 - Bouguer anomaly (solid line) and calculated gravimetric effects (dashed line) relative to: two West-Est sections of the density model and to the first iteration.

Fig. 3 - Scatter plot of the correlation Vs → Vp with a superposition of the Brocher’s relationships (solid line). a): DWS>1000; b): DWS>5000. − After the spatial analysis of the gravimetric residues distribution (gb - gc ) it has been determined the minimum norm density correction vector. This vector was chosen among all those that generate max min gravimetric effects between gc and gc . The correction distribution is used both to make small corrections to the Brocher’s density-velocity correlation equations (ρ -Vp, ρ -Vs), averaged on a very extended experimental case study, and to determine two correction vectors for Vp and Vs models respectively, through the previous Eq. (2) and the following Brocher’s equation:

(4)

Using the corrected Vp and Vs distributions as input for a new tomographic inversion the velocity and density models are iteratively upgraded. The application of the proposed procedure to the Sicilian area underlined the necessity of the integration of these different kinds physical information to construct lithospheric models, although the seismic problem seemed to be a priori well constrained. Furthermore, it allowed to highlight some velocity and density features that could play a crucial rule for the reconstruction of the geodynamic evolution of the study area. References Brocher M. T. (2005). Empirical Relations between Elastic Wavespeeds and Density in the Earth’s Crust. Bulletin of the Seismological Society of America, Vol. 95, No. 6, pp. 2081–2092.

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Caló M., Dorbath C., Luzio D., Rotolo S. G., D'anna G. (2009). Local Earthquake Tomography in the Southern Tyrrhenian Region of Italy: Geophysical and Petrological Inferences on the Subducting Lithosphere. Frontiers in Earth Sciences - Subduction Zone Geodynamics - Springer Berlin Heidelberg, pp. 85-99. Calò M., Dorbath C., Luzio D., Rotolo S.G., D’Anna G., (2008). WAM Tomography in the southern Tyrrhenian region. Petrological inferences and hypothesis on the fluid circulation in the subducting Ionian slab and adjoining mantle domains, Bollettino di Geofisica Teorica ed Applicata Vol. 49 (2), 136-141. Nagy, D., 1966. The gravitational attraction of a righ rectangular prism. Geophysics 31, 362–371. Snopek, K., Casten, U. (2006) 3GRAINS: 3D Gravity Interpretation Software and its application to density modeling of the Hellenic Subduction Zone, Computers & Geosciences, 32, 592-603.

THE NANGA PARBAT-HARAMOSH MONITORING NETWORK G. Poretti1, C. Calligaris2, S. Tariq3, Hawas Khan4, F. Zubair3 1 University of Trieste, Italy – DMI 2 University of Trieste, Italy – DiSGAM 3 Bahria University, Pakistan - DE&ES 4 Karakorum International University, Gilgit – DES

Introduction. If the Himalayas are a land of extremes from the topographical, geophysical and geological point of view (Windley, 1984, 1988), the Karakorum is a land of superlatives, having the highest concentration of mountains over 8000 metres, having the longest glaciers outside of the poles, being the source of one of the longest rivers. From the geophysical point of view it contains the largest gravity anomalies (Poretti et al., 1983) and thickness of the earth crust (75 km) (Finet- ti et al., 1978, 1983) and the highest values of deflection of the vertical. It also contains the highest relief (4000 metres from the Indus plains to the summit of Nanga Parbat). It seems also that this area is subject to the highest uplift. This has been mentioned by many authors who derived it

Fig. 1. Regional geological setting of the Nanga Parbat-Haramosh massif (modified after Gansser [1964]; Coward, et. al., [1988]; Searle, et. al., [1988]; Greco and Spencer, [1993].

187 GNGTS 2009 SESSIONE 1.2 through indirect methods, but had not yet been confirmed by accurate direct observations. Lewis Owen reports 0.7 mm/y using fission-track methods (Owen, 1981). Higher values (2 mm/y) are inferred by several researchers (Zeitler 1985, Gorniz and Seeber 1981; Lyon-Caen and Molnar 1983; Ferguson, 1985 and again Owen, 1989). Finally an average value of 6-10 mm/y was in the hypothesis of Zeitler et al. 1985 including uplift and erosion. These values were calculated through indirect methods, but no tentative was made to calculate the uplift of the Nanga Parbat - Haramosh massif through direct surveys. The present study shows the preliminary results of a first survey consequent to the installation of a GNSS network including three permanent GNSS stations between Islamabad and the Northern Areas of Pakistan and four points located on the Nanga Parbat – Haramosh massif. These points will be surveyed once a year during the next 6 years and will provide a fair record of their movements, both horizontal and vertical, with respect to the surrounding areas. During the processing of the surveyed data, the observations of the International GPS Net- work Kit3 situated at in Uzbekistan will be taken into account. Another problem tackled by this research is the determination of the stability of the two banks of the Indus river in the area where the Diamer Basha dam is being built. The repeated measurements, before, during and after the construction of the dam will be an important index of the change in the geophysical parameters produced by the dam and the related lake. GPS and classical distance measurements will be performed on a network of 6 points located on both sides of the river. Regional Geology and Plate Tectonic Setting. Northern Pakistan comprises three former distinct and previously separate plates named Karakoram, Kohistan and Indian plates. These plates collided with each other during the Cretaceous-Tertiary ages and formed the present day configuration of this region (Tahirkheli et al., 1982; Coward et al., 1987). This collisional tectonics and mountain-building activity is termed “Himalayan Orogeny” being the result of continent-arc-continent collision. The Kohistan Island Arc is sutured to the Karakoram Block (Shyok Suture) in the north along the MKT (Main Karakoram Thrust) and to the Indian Plate (Indus-Tsangpo Suture) in the south. The tectonics of Kohistan is related to the collisional tectonics of the Hindu Kush, Karakoram and Himalayan Ranges which involve the Indian plate, with the Nanga Parbat- Haramosh Massif sandwiched between the Kohistan and Ladakh island arcs.. Geology of the Nanga Parbat area. The Nanga Parbat–Haramosh massif is delimited by two thrust-displacement shear zones that have a spatial and temporal link with granite plutonism from ca. 10 to 1 Ma. The shear zones define a crustal-scale antiformal pop-up structure, with dominant west-northwest–vergent and subordinate east-southeast–vergent thrusting. This is substantially

Fig. 2 - Geological map of the Nanga Parbat-Haramosh massif (from Butler et al., 1992; Lemennicier et al., 1996; Greco and Spencer, 1993; Fontan and Schouppe, 1995; Edwardset al., 1997).

188 GNGTS 2009 SESSIONE 1.2 different from the surrounding area where the main exposed Himalayan structures are oriented parallel to the orogenic trend and are early to middle Miocene or older (Schneider et al., 1999). The western Himalaya syntaxis includes the Nanga Parbat–Haramosh massif, a now exposed section of largely Proterozoic Indian plate crust, initially overthrusted by Cretaceous island arc rocks along the Main Mantle thrust. Nanga Parbat is an area of extreme relief that has undergone rapid exhumation since 10 Ma (e.g., Zeitler, 1985), exposing migmatites and granulitegrade rocks at the core of the massif (Smith et al., 1992). Nanga Parbat syntaxis comprises three major rock units: a) Iskhere- Mushkin-Rupal Gneiss; b) Shengus-Harchu Gneiss; c) Haramosh-Tarshing Schists. A wide range of rocks intruding these major lithological units has been noticed in nearly all of the Nanga Parbat syntaxial region, which includes basic dykes and a wide variety of granites. The younger phases of granite up to 0.75 Ma are intruding the Nanga Parbat Gneisses. Geophysical constraints a) Seismology The epicentres distribution of the main earthquakes (m>4) were analysed confirming that the seismic activity is mainly prevalent along the MMT. b) The gravity field Airy and Bouguer gravity anomalies were computed along 3 profiles crossing the massif. A remarkable deepening of the already negative anomalies was found on all profiles reaching to a value of -70 mgal. c) Magnetic anomalies The anomalies provided rather low values except at margins of the massif i.e. in Bunji and in Khume, suggesting an outcrop of ferro-magnetic rocks along the margins of the massif. The selected points and their monumentation: The selection of the points. The NPH massif is surrounded by the Main Mantle Thrust between Kohistan and Ladakh. In order to determine its movements, both horizontal and vertical, a network of GNSS stations has been planned, including four points on the massif (Harchu, Rama, Shengus, Fairy Meadows) four on the surrounding area (Gilgit, Chilas, Skardu and Muzaffarabad) but external to the MMT. One point was located in Islamabad (Bahria University), completely external to the investigated tectonic area. The location of the Diamer Basha dam. Six points were monumented along the Indus River where the dam will be built. Three on each bank, two on the upstream segment, two in correspondence to the dam and two downstream with respect to the line of the dam. Conclusions. No deductions can be drawn after the preliminary survey. The first campaign will be conducted between October and November 2009 and the second in September 2010. Afterwards it will be possible to detect and point out eventual movements of the Massif. References Tahirkheli, R. A., 1982. Geology of the Himalaya, Karakoram, Hindukush in Pakistan. Geol. Bull. Univ. Peshawar. Coward, M. P.., Butler, R. W. H., Khan, M. A. & Knippe, R. J., 1987. The tectonic history of Kohistan and its implications for Himalayan structure. Jour. Geol. Soc. London, 144, 377-391. Khan, M. A., Jan, M. Q. & Weaver, B. L., 1993. Evolution of the lower arc crust in Kohistan, N. Pakistan: temporal arc magmatism through early, mature and intra-arc rift stages. In: Himalayan Tectonics, Spec. Publ.Geol. Soc. London, 74, 123-138. Burg, J.-P., Chaudhry, M. N., Ghazanfar, M., Anczkiewicz, R. and Spencer, D., 1996. Structural evidence for back sliding of the Kohistan arc in the collisional system of northwest Pakistan. Geology 24, 739-742. Butler, R.W.H., George, M., Harris, N.B.W., Jones, C., Prior, D.J., Treloar, P.J., and Wheeler, J., 1992. Geology of the northern part of the Nanga Parbat massif, northern Pakistan, and its implications for Himalayan tectonics. J. Geol. Soc., 149, 557-567. Gansser, A., 1964. Geology of the Himalaya. Wiley Interscience, London. 289pp., & 4 plates. Burg, J.-P., Chaudhry, M. N., Ghazanfar, M., Anczkiewicz, R. and Spencer, D., 1996. Structural evidence for back sliding of the Kohistan arc in the collisional system of northwest Pakistan. Geology, 24, 739-742. Butler, R.W.H., George, M., Harris, N.B.W., Jones, C., Prior, D.J., Treloar, P.J., and Wheeler, J., 1992. Geology of the northern part of the Nanga Parbat massif, northern Pakistan, and its implications for Himalayan tectonics. J. Geol. Soc., 149, 557-567. Schneider, D. A., Edwards, M. A., Zeitler, P. K., and Kidd, W. S. F., 1997. Ion microprobe U-(Th)-Pb and Ar/Ar geochronology of Nanga Parbat - Haramosh Massif (part 1). Rupal Valley, southern Nanga Parbat, and Jutial granite, Haramosh area. in Angiolini, L., et al. eds., 12th Himalaya-Karakoram-Tibet Workshop - Abstract Volume, Accademia Nazionale dei Lincei., 205-206.

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NUMERICAL SIMULATION OF OCEAN/CONTINENT CONVERGENT SYSTEMS: INFLUENCE OF SUBDUCTION GEOMETRY AND MANTLE WEDGE HYDRATION ON CRUSTAL RECYCLING M. Roda 1-2, A.M. Marotta 1, M.I. Spalla 2 1 Università degli Studi di Milano, Dipartimento di Scienze della Terra Ardito Desio, Sezione di Geoﬁsica 2 Università degli Studi di Milano, Dipartimento di Scienze della Terra Ardito Desio, Sezione di Geologia

Studies on high-pressure (HP) and ultrahigh-pressure (UHP) rocks exposed in orogenic belts linked to collisional margin show that nappes of oceanic and continental deeply subducted crust can be exhumed to shallow structural levels. In particular, during ocean-continent-type subduction, the crustal material dragged into subduction channel is composed chiefly by ocean and trench sediments, crustal slices belonging to subducting plate [microcontinent (Ring & Layer, 2003) or linked to early continental collision (Chemenda et al., 1995)] or crustal slices tectonically eroded from the overriding plate (ablative subduction) (Tao & O’Connell, 1992, Marotta & Spalla, 2007). Several models have been developed, during last 20 years, to analyse exhumation of subducted crustal material. They can be resume on five main mechanisms: a) crustal-mantle delamination (Chemenda et al., 1995), b) slab break-off (Ernst et al., 1997), c) slab retreat (Ring & Layer, 2003) and roll-back slab (Brun & Faccenna, 2008) and d) decoupling of two main ductile layers (Yamato et al., 2008), in which the exhumation is mainly driven by negative buoyancy and/or faulting and e) subduction- channel flow (Gerya & Stockhert, 2005) in which the exhumation is driven by the upwelling flow developed in low-viscosity mantle wedge. Only channel flow takes into account recyrculation of crustal slices dragged to high depth by ablation in pre-collisional subduction zones. To study the effects of subduction rate, slab dip and mantle rheology changes on channel flow efficiency a para- metric analysis is made. We present the results of a set of numerical simulation with different subduction rates, slab dips and mantle rheology represented by dry dunite and dry olivine flow laws. Numerical model predictions are finally compare to some PT paths obtained from ancient and actual subduction zones with different slab dips and convergence velocities. A general good agreement between natural data and model predictions emerges from the comparison: exhumation rates obtained from complete PTt-paths (total exhumation rates) are more compatible with natural rates rather than maximum exhumation rates; the thermal states predicted by ablative subduction simulations with a hydrated mantle wedge justify the natural PT estimates obtained on continental crust units involved in ocean/continent subduction systems. For these reasons, we propose ablative subduction of the upper continental plate linked to hydrated mantle wedge as a good alternative pre-collisional mechanism, with respect to the collisional mechamisms as the slab break-off, slab-retreat and roll-back slab. References Brun J-P, Faccenna C.; 2008: Exhumation of high-pressure rocks driven by slab rollback. Earth and Planetary Science Letters, 272, 1-7. Chemenda A. I., Mattauer M., Malavieille J., Bokun A.N.; 1995: A mechanism for syn-collisional rock exhumation and associated normal faulting: Results from physical modelling. Earth and Planetary Science Letters, 132, 225-232. Ernst W.G., Maruyama S., Wallis S.; 1997: Buoyancy-driven, rapid exhumation of ultrahigh-pressure metamorphosed continental crust. Proc. Natl. Acad. Sci., 94, 9532-9537. Gerya T.V., Stockhert B.; 2005: Two-dimensional numerical modeling of tectonic and metamorphic histories at active continental margins. Int. J. Earth. Sci. (Geol Rundsch), 95(2). Ring U., Layer P. W.; 2003: High-pressure metamorphism in the aegean, eastern mediterranean: Underplating and exhumation from the late cretaceous until the miocene to recent above the retreating hellenic subduction zone. Tectonics, 22(3). Spalla, M.I. & Marotta, A.M., 2007. P-T evolutions vs. numerical modelling: a key to unravel the Paleozoic to early-Mesozoic tectonic evolution of the Alpine area. Periodico di Mineralogia, 76, 267-308. Tao W.C., O’Connell R.J.; 1992: Ablative subduction: A two-sided alternative to the conventional subduction model. Journal of Geophysical Research, 97(B6), 8877-8904. Yamato P., Burov E., Agard P., Pourhiet L.L., Jolivet L.; 2008: HP-UHP exhumation during slow continental subduction: self- consistent thermodynamically and thermomechanically coupled model with application to the western alps. Earth and Planetary Science Letters, 271, 63-74.

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UPLIFT AND FOLDING OF PLEISTOCENE MARINE TERRACES ALONG THE IONIAN SEA COAST OF NORTHERN CALABRIA: FIELD ANALYSIS AND MODEL RESULTS E. Santoro1, L. Ferranti2, C. Monaco1, P. Burrato3 1 Dipartimento di Scienze Geologiche, Università di Catania, Italy 2 Dipartimento di Scienze della Terra, Università di Napoli, Italy 3 INGV, Rome A detailed study of uplifted Middle-Late Pleistocene marine terraces on the eastern side of northern Calabria and Basilicata provides insights into the temporal and spatial scale variability of vertical displacement rates over a time span of ~600 ka, and allowed to model the recent activity of transpressional faults in the area. This region is located on the northeastern tip of the Calabrian arc, which lies above the westerly-plunging Ionian slab, and a combination of lithospheric and crustal processes concurred to rapid Late Quaternary uplift (Westaway, 1993; Wortel and Spakman, 2000; Gvirtzman and Nur, 2001). Ten terrace orders were mapped up to 663 m a.s.l., and were correlated between the coastal slopes of Pollino and Sila mountain ranges across the Sibari Plain, facing the Ionian Sea side of north-eastern Calabria and eastern Basilicata (Fig. 1). Radiometric (ESR and 14C) dating of shells provides a chrono-stratigraphic scheme for the Late Pleistocene terraces (Santoro et al., 2009). The age of higher terraces is poorly constrained, but, based on the uplift rate deduced from the Tyrrhenian marker (~1 mm/a), conceivably is tracked back to MIS 15 (~620 ka). Based on the terrace chronology, uplift in the last ~600 ka occurred at an average rate of 1 mm/a, but was characterized by the alternation of more rapid (~2.5 mm/a) and slower (~0.16 mm/a) periods of displacement (Fig.2b). Besides, spatial variability in uplift rates is recorded by the deformation profile of terraces parallel to the coast (Fig.2a), which document small-wavelength (~2-10 km) and amplitude (~10-50 m) local undulations superposed to the regional uplift pattern, which is the dominant tectonic signal (Santoro et al., 2009). The local structures spatially coincide with the last generation folds and locally with southward-directed left-transpressional faults mapped in bedrock (Catalano et al., 1993; Monaco et al., 1998) and locally in fan-delta deposits, striking orthogonal to the coastline, and involving the sea-bottom along their offshore extension (Fig. 3; Ferranti et al., 2009). Structural analysis and appraisal of local network seismicity (Fig. 3) and regional GPS geodesy suggests that the area is experiencing transpressional deformation in response to NE-SW shortening; this explains the origin of the local-scale undulations in the deformation profile of paleo-shorelines as due to fault-related crustal anticline and syn- Fig. 1 - Morphological map of the Middle Pleistocene–Holo- cene marine terraces on the Ionian coast of northern Calabria cline (Ferranti et al., 2009). and eastern Basilicata.

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Fig. 2 – a) Coast-parallel profiles of the inner edge elevation of Middle-Late Pleistocene marine terraces in Northeastern Calabria and eastern Basilicata. b) Uplift rate history from ~600 ka to ~60 ka for five different transects along the coast of northeastern Calabria and eastern Basilicata.

Fig. 3 - Seismotectonic setting of northeastern Calabria. White dots are epicenters of 1981–2002 instrumental seismicity from the Istituto Nazionale di Geofisica e Vulcanologia (INGV) database (http://www.ingv.it/CSI/); grey dots are epicenters of 1966–2003 instrumental seismicity (MN2) from the Advanced Seismic Station Network (ASSN) database (http://earthquake.usgs.gov/research/monitoring/anss/). Focal mechanisms of moderate (2.3

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Fig. 4 – Fault segments used in the numerical model.

The recent tectonic activity of the major faults was supported by a morpho-tectonic analysis. We used the SL index, Vf index and the hypsometric integral in order to identify drainage network anomalies, and the residual topography and the swath profiles to charac- terize the landscape. All the indexes are poorly linked to lithological and climatic factors, and anomalies were found to be spatially related to the faults inquired to cause the paleo shore-lines deformation. On-shore and offshore faults were grouped in geometrically coherent systems of faults of assigned length, dip and kinematic parameters. This selection was the basis for a numerical modeling of the coseismic deformation associated to the transpressional faults which could reproduce the observed deformation profile of paleo- shorelines. The model is base on two major assump- tions: a) the earth is assumed to be an elastic half- space; b) the faults are assumed to be rectangular shaped. The geometrical fault parameters (strike, plunge, dip, length, width, area, minimum and maximum depth) were derived from geological cross sections, offshore seismic reflection profiles and morphological evidences. The fault rake were derived from structural analysis, GPS velocity data and focal mechanisms. We modeled ten fault zones (Fig. 4), for a total of 25 fault segments. Fig. 5 shows the model result for terraces T4 (MIS 5.5, 124 ka) and T3 (MIS 5.3, 93 Ka).

Fig. 5 – a) Comparison between model result and observed elevation for terraces T3 and T4. Right-hand histogram shows the quantification of local and regional uplift rate. b) Time partitioned uplift rate in the last 124 Ka along the Corigliano-Rossano, Satanasso and Valsinni fault zones.

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Coseismic deformation of the transpressional faults matches to a large degree the differential elevation attained by the paleo-shorelines (Fig. 5a). The uplift of the studied coastal area is mainly controlled by a regional source; the local fault uplift reach a maximum of 20% of the total uplift that affect the region. Fault activity was mostly concentrated in the central-northern part of the area between the northern Sibari plain and the Pollino coast (Fig. 5a, right-side histograms). We also find that fault activity not only changed through time for individual faults (and for the cumulative fault array), but also shifted among single faults. Fig.5b shows the vertical tectonic displacement rate related to the activity of the major transpressional faults for the time intervals 124- 93 Ka and 93-0 Ka, for which terrace analysis provided the more accurate information. It is evident that the northernmost, northward-directed Valsinni fault has accrued the largest deformation during the Late Pleistocene, although about half of the displacement rate was shifted to the nearby Satanasso fault after 93 ka; in the meantime, slip on the southernmost Corigliano-Rossano fault dra- matically decreased. References Catalano S., Monaco C., Tortorici L., Tansi C.; 1993. Pleistocene strike-slip tectonics in the Lucanian Apennine (Southern Italy). Tectonics, 12, 656–665. Ferranti L., Santoro E., Mazzella M.E., Monaco C., Morelli D.; 2009. Active transpression in the northern Calabria Apennines, southern Italy. Tectonophysics, 476 (1-2), 226-251 (in press). Frepoli A., Amato A.; 2000. Fault plane solutions of crustal earthquakes in Southern Italy (1988–1995): seismotectonic implications. Ann. Geophys., 43 (3), 437–468. Gvirtzman Z., Nur A.; 2001. Residual topography, lithospheric structure and sunken slabs in the central Mediterranean. Earth Planet. Sci. Lett., 187, 117–130. Monaco C., Tortorici L., Paltrinieri W.; 1998. Structural evolution of the Lucanian Apennines, southern Italy. J. Struct. Geol., 20, 617–638. Santoro E., Mazzella M.E., Ferranti L., Randisi A., Napolitano E., Rittner S., Radtke U.; 2009. Raised coastal terraces along the Ionian Sea coast of northern Calabria, Italy, suggest space and time variability of tectonic uplift rates. Quaternary International, 206, 78–101 (in press). Westaway R.; 1993: Quaternary uplift of southern Italy. J. Geophys. Res., 87, 21741–21772. Wortel M.J.R., Spakman W.; 2000. Subduction and slab detachment in the Mediterranean–Carpathian region. Science, 290, 1910–1917.

CAN LOCAL EARTHQUAKE TOMOGRAPHY SETTLE THE MATTER ABOUT SUBDUCTION IN THE NORTHERN AND CENTRAL APENNINES? D. Scafidi 1, S. Solarino 2, C. Eva 1 1 Dip.Te.Ris., Università degli Studi di Genova 2 INGV Istituto Nazionale di Geofisica, c/o Dip.Te.Ris., Genova

Seismic tomography is the most powerful tool to investigate large volumes of the earth. The three dimensional inversion of teleseismic earthquakes provides poorly detailed information on large and deep bodies, while local earthquake tomography has the potential to display smaller anomalies but down to a depth limited by the deeper earthquakes included in the inversion. Although many geological, geophysical and geodynamical studies have been conducted on the Italian area, there are still open questions, and different models have been proposed to explain the present-day structural setting. Some of the most debated questions are the presence or not of continuous subduction under the Apennines, and the presence or not of a slab detachment in the northern or in the central part of the Apenninic chain. The absence of a continuous, high velocity body beneath the Apennines has been interpreted by some researchers (Wortel and Spakman, 2000) as an evidence of the detachment of the Apenninic slab. According to this view the Apenninic slab is expected to be inactive whether the Ionian lithosphere subducting underneath Calabria is considered to be on the verge of detaching or just detached. Other researchers (Guegen et al., 1998), however, suggest that a fairly continuous and fast slab exists beneath the Apennines and the Calabrian

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Fig. 1 - Tomographic cross-sections perpendicular to the northern and central Apennines. For each section the topographic profile, the Vp values in absolute velocities (km/s) and the Vp/Vs ratio are reported.

195 GNGTS 2009 SESSIONE 1.2 arc. Different geodynamical models have also been proposed for the Tyrrhenian area considering it as an active (Faccenna et al., 1996) or as a passive margin (Lavecchia et al., 2003; Scalera, 2005). In previous works, our working group has conducted several seismic tomographies with both techniques in the search of the geometry, size and extension with depth of the subduction under the Italian peninsula. While the images resulting from teleseismic data were clearly showing a subducting slab under the Calabrian arc, they were not conclusive for the rest of the Apennines since they were showing, only in the Northern sector, a likely subduction in the shallower part apparently detached from other high velocities body in the deeper zone. At that stage it was not possible to dis- tinguish between thrust and subduction due to the poor horizontal resolution of the applied methodology. More recently, a local earthquake tomography has given details about this shallower sector but again was not able to clearly display a subducting slab. The main limitation of this tomography is the lack of seismic events deeper than 60-70 km under the northern and central Apennines. The absence of seismicity itself can be not considered an evidence of non-subduction as some authors showed that different rheological behaviours of the continental versus oceanic lithosphere can account for the shallower and subcrustal seismicity below the northern Apennines with respect to deeper and more intense seismicity below the Calabrian arc. In particular, the low seismicity or aseismic behaviour of orogenic roots or slabs may in some cases be ascribed to a ductile deformation of quartz-feldspar rich subducting continental lithosphere rather than to the absence of active subduction. In practice the kind of seismicity may depend on reasons different from the subduction, and should not be considered evidence for the presence of it. In order to analyse in more details this apparent discrepancy, a new seismic tomography is presented in this work. A very dense grid, the selection of a smaller area to be investigated (limited to the Apennines only) and the addition of new data partly improved the results, which cannot anyway go beyond the maximum depth of seismic events. Analysing different cross sections of these enhanced resolution tomography results, we do not see any slab in the northern-central Apennines in the first 100 km depth. The downgoing material (Adriatic plate) of this area has a rather low dip angle, as also partly shown by the distribution of the (few) deep seismic events. Along the central and also the northern part of the Apennines there are more overlapping geometries than subducting geometries. Bibliografia Faccenna C., Davy P., Brun J.P., Funiciello R., Giardini D., Mattei M., Nalpas T.; 1996: The dynamics of back-arc extension: an experimental approach to the opening of the Tyrrhenian Sea. Geophys. J. Int., 126, 781-795. Guegen E., Doglioni C., Fernandez M.; 1998: On the post-25 Ma geodynamic evolution of the western Mediterranean. Tectonophysics, 298, 259-269. Lavecchia G., Boncio P., Nicola C., Francesco B.; 2003: Some aspects of the Italian Geology not fitting with a subduction scenario. Journal of Virtual Explorer, 10, 1-14. Scalera G.; 2005: A new interpretation of the Mediterranean arcs: Mantle wedge intrusion instead of subduction. Boll. Soc. Geol. It., Volume speciale, 5, 129-147. Wortel M.J.R., Spakman W.; 2000: Subduction and Slab Detachment in the Mediterranean-Carpathian Region. Science, 290, 1910- 1917.

QUALE GEODINAMICA PER LO STRETTO DI MESSINA? G. Scalera Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Roma1

Gli studi sulla geodinamica dello stretto di Messina sono stati sempre oggetto della attività dei geologi italiani e stranieri da più di un secolo (Faggiotto, 1895, 1900; Taramelli, 1910; Pata, 1954; e molti altri fino ad oggi). Solo più recentemente gli innumerevoli studi geologici e geofisici sono stati affiancati da strumenti geodetici satellitari (Devoti et al, 2002; e molti altri) che con una precisione scesa ormai al di sotto del millimetro, ritengono di poter definire la direzione e il tasso di spostamento annuo della Sicilia rispetto al continente.

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Fig. 1. Distribuzione degli ipocentri del margine pacifico del Sud America (dati del Catalogo Globale di Engdhal et al, 1998; le sferette nere rappresentano gli apparati vulcanici). La zona di Wadati-Benioff è divisa in clusters le cui caratteristiche morfologiche sono incompatibili con la ‘subduzione’. Si veda il dettaglio del cluster di Arica in Fig. 2.

Da pochi anni, il catalogo globale degli ipocentri rilocati di Engdhal et al. (1998) ha consentito di riconoscere come non valida l’assunzione che le zone di Wadati- Benioff siano superfici planari o a cucchia- io (Scalera, 2008). Queste zone sono invece caratterizzate da clusters o grappoli di ipocentri con una struttura tipica ad ‘albe- ro’, rastremata in profondità e che tende ad allargarsi ‘a chioma’ verso la Moho e la crosta (Scalera, 2008). Particolarmente spettacolare la situa- zione relativa al Sud America (Fig. 1), dove una serie di tali clusters affonda in profondità in direzioni anche totalmente discordi rispetto a quella attesa. Ad esempio, il cluster sotto la città di Arica è chiaramente diretto verso Nord (Fig. 2). Nel mediterraneo o più in generale nella lunga regione tetidea, si osserva in effetti, al posto di una attesa superficie regolare di ipocentri profondi, una serie di clusters ipocentrali singoli ed iso- lati nelle zone sintassiali dell’Himalaya, nei Carpazi meridionali (regione del Vrancea), nell’Arco Ellenico e nel Tirreno Meridionale. Tutte queste zone sono collocate dove gli orogeni assumono una curvatura massima ed in regioni in chiaro sollevamento attivo, richiamando una geodinamica molto diversa da quella oggi cor- rentemente accettata. Da molti indizi con- comitanti il concetto di subduzione a grande scala sembrerebbe essere escluso da un processo inverso, di sollevamento pilotato da cambiamenti di fase del mantello in un regime distensivo (Scalera, 2008). La semplice assenza di un cluster di ipocentri profondi nella zona di massima curvatura delle Alpi occidentali, dove un grande sollevamento è già concluso con la esposizio- ne della finestra tettonica di Ivrea, sembra confermare l’ipotesi (Scalera, in stampa). In ogni caso la subduzione a grande scala (centinaia di chilometri) non deve essere confusa con i sovra e sotto-scorrimenti Fig. 2 - Distribuzione degli ipocentri del cluster (poche decine di chilometri) dei quali esi- sudamericano sotto la città di Arica (settore centrale delle ste ampia documentazione geologica. Ande; dati del Catalogo Globale di Engdhal et al, 1998; la Si dovrebbe quindi riflettere sulla freccia nera indica il nord). Il cluster di ipocentri profondi ancora grande incertezza in cui si trova sembra formare una conca in superficie che si fa più oggi la comunità scientifica sulla reale profonda e si assottiglia diretta verso il Nord. Una struttura molto simile si osserva sotto Messina.

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Fig. 3 - Ipocentri del Tirreno meridionale (dati del Catalogo Sismico Italiano INGV; le sferette nere rappresentano gli apparati vulcanici). Il cluster principale di ipocentri profondi sembra dividersi in sub-clusters.

Fig. 4 - Superficie della densità massima degli ipocentri del Tirreno meridionale (dati del Catalogo Sismico Italiano INGV). La conca definita fino a circa 150 km di profondità, sembra poi avvitarsi verso Ovest. Una struttura simile ma di dimensioni maggiori è quella mostrata in Fig. 2. geodinamica del Mediterraneo e dello Stretto di Messina in particolare. Bisognerebbe anche soffer- marsi sul fatto che un cambiamento di prospettiva in geodinamica globale (in media uno ogni 50 anni) potrebbe portare a una diversa valutazione dei potenziali tsunamigenico e sismico della regione, suggerendo maggiore prudenza per il presente (riserva che potrebbe sciogliersi nel futuro) nella realizzazione di grandi opere pubbliche quali un ponte sullo stretto di Messina. Bibliografia Devoti R., Ferraro C., Guegen E., Lanotte R., Luceri V., Nardi A., Pacione R., Rutigliano P., Sciarretta C. and Vespe F. (2002). Geodetic control on recent tectonic movements in the central Mediterranean area. Tectonophysics, 346, 151-167. Engdahl E.R., Van der Hilst R.D. and Buland R.P. (1998). Global teleseismic earthquake relocation with improved travel times and procedures for depth determination. Bull. Seism. Soc. Amer., 88, 722-743. Scalera G. (2008). Great and old earthquakes against great and old paradigms – paradoxes, historical roots, alternative answers. Advances in Geosciences, 14, 41–57. Scalera G. (2008). Earthquakes, phase changes, fold belts: from Apennines to a global perspective. GeoActa, (in stampa).

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STRAIN ACCUMULATION ACROSS THE MESSINA STRAITS AND KINEMATICS OF SICILY AND CALABRIA FROM GPS DATA AND DISLOCATION MODELING E. Serpelloni 1, R. Burgmann 2, M. Anzidei 1, P. Baldi 3, B. Mastrolembo 3,4 1 Istituto Nazionale di Geofisica e Vulcanologia, Centro Nazionale Terremoti 2 Department of Earth and Planetary Science, University of California, Berkeley, (USA) 3 Dipartimento di Fisica, Settore di Geofisica, Università di Bologna 4 Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Bologna

We use Global Positioning System (GPS) velocities and dislocation modeling to investigate the rate and nature of interseismic strain accumulation in the area affected by the 1908 Mw 7.1 Messina earthquake (southern Italy), constrained in the framework of the complex central Mediterranean micro-plates kinematics. Our data confirm a change in the velocity trends between Sicily and Calabria, moving from NNW-ward to NE-ward with respect to Eurasia, and details a fan-like pattern across the Messina Straits where maximum extensional strain-rates are ~65 nanostrain/yr. Extension normal to the coasts of Sicily is consistent with the presence of SW-NE trending normal faults. Half space dislocation models of the GPS velocities are used to infer the slip-rates and geometric fault parameters of the fault zone that ruptured in the Messina earthquake, obtaining optimal values of 3.5 and 1.6 mm/yr for the dip-slip and strike-slip components, respectively, along a 30° dipping normal fault, locked above 7.6 km depth. By developing a regional elastic block model that accounts for both crustal block rotations and strain loading at block-bounding faults, we show that the measured velocity gradient across the Straits may be significantly affected by the elastic strain contribution from other nearby faults. In particular, when considering the contribution of the possibly locked Calabrian subduction interface onto the observed velocity gradients in NE-Sicily and SW-Calabria, we find that this longer wavelength signal can be presently super-imposed on the observed velocity gradients in NE-Sicily and Calabria. The inferred slip rate on the Messina fault is impacted by elastic strain from Calabria; higher locking on the subduction thrust allow for substantially higher slip rates on the normal fault.

Fig. 1 - Geodetic strain rate field computed over a regular 2x2°. Black and dark grey arrows show extensional and compressional strain rates, respectively. Grey crosses display 1σ uncertainties. Light grey arrows show residual GPS velocities with respect to a Nubian fixed frame.

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ASSETTO SISMOTETTONICO DELL’APPENNINO CENTRALE: EVIDENZE GEOLOGICHE, SISMOLOGICHE E GEODETICHE M. Viti, E. Mantovani, D. Babbucci Dipartimento di Scienze della Terra, Università degli Studi di Siena

L’assetto strutturale dell’Appennino centrale deriva in gran parte dalla fase orogenica che dal tardo Miocene ha causato il forte raccorciamento della piattaforma carbonatica laziale-abruzzese (e.g. Finetti et al., 2005; Calamita et al., 2006 e riferimenti). La tettonica compressiva ha generato una serie di rilievi sub-paralleli orientati circa NO-SE (Volsci, Ernici-Simbruini, Marsica, Velino- Sirente-Genzana-Montagna Grande, Morrone-Pizzalto). La presenza di archi strutturali, tra cui in particolare quello del Gran Sasso, suggerisce l’azione di una compressione parallela alla catena (Mantovani et al., 2008a; Satolli e Calamita, 2008). Tale ipotesi è compatibile con il raccorciamen- to sul fronte esterno e la coeva estensione nella zona interna, che ha presumibilmente generato i bacini fluvio-lacustri interposti tra i rilievi principali (Sacco, Liri-Val Roveto, Salto, Fucino, Sangro, Aquila, Aterno e Sulmona, e.g. Galadini e Messina, 2001, 2004). Il quadro tettonico sopra descritto ha subito un significativo cambiamento attorno al Pleistocene medio, in accordo con quanto osservato negli altri settori dell’Appennino (e.g. Hippolyte et al., 1994; Viti et al., 2006). L’analisi integrata del notevole insieme di evidenze attualmente disponibili sul quadro deformativo recente dell’Appennino centrale e zone adiacenti suggerisce infatti un regime transtensivo sinistro, con direzione di massimo allungamento circa NNE-SSW (Cello et alii, 1995, 1997; Amoruso et al., 1998; Galadini, 1999; Piccardi et alii, 1999, 2006; Galadini e Messina, 2001; Tondi e Cello, 2003). La complessa fatturazione sopra descritta potrebbe essere l’espressione superficiale di una zona di taglio profonda a cinematica sinistra, come suggerito anche dal meccanismo focale di eventi sismici recenti. Questo regime è compatibile con il quadro geodinamico a larga scala che può spiegare in modo semplice e coerente il complesso delle deformazioni post- Pleistocene medio riconosciute nell’intera regione centro mediterranea (Mantovani et al., 2008a,b, 2009). In questo contesto tettonico regionale, il recente terremoto dell’ Aquila, associato ad una faglia normale (Anzidei et al., 2009; Atzori et al., 2009; Walters et al., 2009), può essere interpretato come un effetto dell’estensione orientata circa NE-SO che si sviluppa nella parte interna del- l’arco del Gran Sasso. Questo si delinea quindi come un esempio in cui la deformazione locale osservata evidenzia un regime notevolmente diverso da quello che produce la deformazione regionale, che nel caso considerato è costituita dalla compressione parallela alla catena, responsabile del- l’arcuamento dell’arco del Gran Sasso. In questa nota verranno mostrate le evidenze geologiche e geofisiche che hanno portato all’interpretazione sopra citata. Inoltre, verranno fatte alcune conside- razioni sul campo di velocità geodetiche dell’Appennino Centrale e Settentrionale, ottenuto da una rete abbastanza densa di stazioni GPS permanenti (vedi nota presentata da Cenni et al.). Bibliografia Amoruso A., Crescentini L., Scarpa R.; 1998: Inversion of source parameters from near- and far-field observations: an application to the 1915 Fucino earthquake, central Apennines, Italy. J. Geophys. Res., 103, 29989-29999. Anzidei M., Boschi E., Cannelli V., Devoti R., Esposito A., Galvani A., Melini D., Pietrantonio G., Riguzzi F., Sepe V., Serpelloni E. ; 2009: Coseismic deformation of the destructive April 6, 2009 L’Aquila earthquake (central Italy) from GPS data. Geophys. Res. Lett., 36, LXXXXX, doi:10.1029/2009GL039145. Atzori S., Hunstad I., Chini M., Salvi S., Tolomei C., Bignami C., Stramondo S., Trasatti E., Antonioli A., Boschi E.; 2009: Finite fault inversion of DInSAR coseismic displacement of the 2009 L’Aquila earthquake (central Italy). Geophys. Res. Lett., 36, L15305, doi:10.1029/ 2009GL039293. Calamita F., Paltrinieri W. Esestime P., Viandante M. G.; 2006: Assetto strutturale crostale dell’Appennino centro-meridionale. Rend. Soc. Geol. Ital. Nuova Ser., 2, 103-107. Cello G., Mazzoli S., Tondi E., Turco E.; 1995: Tettonica attiva in Appennino centrale e implicazioni per l’analisi della pericolosità sismica del settore assiale della catena umbro- marchigiana-abruzzese. Stud. Geol. Camerti, 13, 115-138. Cello G., Mazzoli S., Tondi E., Turco E.; 1997: Active tectonics in the central Apennines and possible implications for seismic hazard analysis in peninsular Italy. Tectonophysics, 272, 43-68. Cenni N., Mantovani E., Baldi P., Viti M., Babbucci D.: Quadro cinematico attuale dell’Appennino centro-settentrionale. Nota presentata al 28° Convegno Nazionale G.N.G.T.S., Trieste 16–19 novembre 2009.

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Finetti I.R., Calamita F., Crescenti U., Del Ben A., Forlin E., Pipan M., Prizzon A., Rusciadelli G., Scisciani V.; 2005: Crustal Geological Section across Central Italy from the Corsica Basin to the Adriatic Sea Based on Geological and CROP seismic data. In: Finetti, I.R. (Ed.), Deep Seismic Exploration of the Central Mediterranean and Italy, CROP PROJECT, Elsevier, pp. 159-196. Galadini F.;1999: Pleistocene change in the central Apennine fault kinematics, a key to decipher active tectonics in central Italy. Tectonics, 18, 877-894. Galadini F., Messina P.; 2001: Plio-Quaternary changes of the normal fault architecture in the central Apennines (Italy). Geodinamica Acta, 14, 321-344. Galadini F. Messina P.; 2004: Early-middle Pleistocene eastward migration of the Abruzzi Apennine (central Italy) extensional domain. J. Geodynamics, 37, 57-81. Hippolyte J.C., Angelier J., Barrier E.; 1994: A major geodynamic change revealed by Quaternary stress patterns in the southern Apennines (Italy). Tectonophysics, 230, 199-210. Mantovani E., Babbucci D., Tamburelli C., Viti M.; 2008a: A review on the driving mechanism of the Tyrrhenian-Apennines system: Implications for the present seismotectonic setting in the Central-Northern Apennines. Tectonophysics, doi: 10.1016/j.tecto.2008.10.032. Mantovani E., Viti M., Babbucci D., Albarello D., Cenni N., Vannucchi A.; 2008b: Long-term earthquake triggering in the Southern and Northern Apennines. J. of Seismology, doi:10.1007/s10950-008-9141-z. Mantovani E., Viti M., Babbucci D., Ferrini M., D’intinosante V., Cenni N.; 2009: Quaternary geodynamics of the Apennine belt. Il Quaternario, 22, 97-108. Piccardi L., Gaudemer Y., Tapponnier P., Boccaletti M.; 1999: Active oblique extension in the central Apennines (Italy): evidence from the Fucino region. Geophys. J. Int., 139, 499-530. Piccardi L., Tondi G., Cello G.; 2006: Geo-structural evidence for active oblique extension in South-Central Italy. In: Pinter N. et al. (Eds.), The Adria microplate: GPS Geodesy, Tectonics and Hazard. Springer, 95-108. Satolli S., Calamita F.; 2008: Differences and similarities between the central and the southern Apennines (Italy): Examining the Gran Sasso versus the Matese-Frosolone salients using paleomagnetic, geological, and structural data. J. Geophys. Res., 113, B10101, doi: 10.1029/2008JB005699. Tondi E., Cello G.; 2003: Spatiotemporal evolution of the central Apennines fault system (Italy). J. Geodynamics, 36, 113-128. Viti M., Mantovani E., Babbucci D., Tamburelli C.; 2006: Quaternary geodynamic evolution and deformation pattern in the Southern Apennines: implications for seismic activity. Boll. Soc. Geol. It., 125, 273-291. Walters R. J., Elliott J. R., D’Agostino N., England P. C., Hunstad I., Jackson J. A., Parsons B., Phillips R. J., Roberts G. ; 2009: The 2009 L’Aquila earthquake (central Italy): A source mechanism and implications for seismic hazard. Geophys. Res. Lett., 36, L17312, doi:10.1029/2009GL039337.

LONG-TERM SURFACE DEFORMATION ANALYSIS IN VOLCANIC AND SEISMOGENIC AREAS VIA THE SBAS-DINSAR APPROACH G. Solaro1,2, A. Manconi2, M. Manunta2, M. Manzo2, S. Pepe2, P. Tizzani1,2, G. Zeni2, R. Lanari2 1 Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Napoli, Osservatorio Vesuviano, Naples, Italy 2 IREA-CNR, Italy

Differential Synthetic Aperture Radar Interferometry (DInSAR) is a remote sensing technique that allows us to produce spatially dense deformation maps with centimeter to millimeter accuracy. An effective way to detect and follow the temporal evolution of deformation is via the generation of time-series; to do this, the information available from each interferometric SAR data pair must be properly related to those included in the other ones, via the generation of an appropriate sequence of DInSAR interferograms. In this context, several approaches have been already proposed. Among these procedures, we consider the one referred to as Small Baseline Subset (SBAS) approach that implements an appropriate combination of DInSAR interferograms generated from SAR images pairs characterized by a small spatial and temporal separation (baseline) between the acquisition orbits (Berardino et al., 2002). We remark that the SBAS algorithm allows us to exploit averaged (multilook) interferograms; this permits to reduce the amount of data to be processed, thus simpli- fying the analysis of extended areas (typically of about 100X100 km). In order to generate long- term time series the basic SBAS technique can be trivially extended by combining data acquired by

201 GNGTS 2009 SESSIONE 1.2 different sensors, i.e., ERS and ENVISAT. Following the first scientific exploitations, the ERS- ENVISAT deformation time-series represent nowadays a very relevant element in monitoring scenarios as testified by their use in several systems aimed at mitigating natural risks. In this work we present several experiments relevant to different sites. The presented results are based on the exploitation of ERS and ENVISAT SAR images and are focused on Etna volcano, Istanbul, Lazufre volcanic area (Chile) and Napoli Bay area, the latter including three volcanic systems (the Campi Flegrei caldera, the Somma-Vesuvio volcanic complex and the Ischia island) and the city of Napoli. The presented results demonstrate the unique opportunity provided by the available 18 years of ERS and ENVISAT acquisitions for better understanding the long term deformation phenomena in volcanic and seismogenic areas and developing effective monitoring scenarios. Moreover, we present first results of 6 April 2009 L’Aquila earthquake to show the key role played by SAR interferometry during an emergency response scenario following an earthquake, for rapidly mapping the permanent ground deformation, unambiguously constraining the slipping nodal plane of the seismic event focal mechanism and retrieving the earthquake source parameters at depth. References Berardino P., Fornaro G., Lanari R. and Sansosti E.; 2002: A new Algorithm for Surface Deformation Monitoring based on Small Baseline Differential SAR Interferograms, IEEE Trans.Geosci. Remote Sens., Vol. 40, No 11, pp. 2375-2383.

TECTONIC ANALYSIS VS NUMERICAL MODELLING: ADVICES FROM THE ALPINE BELT M.I. Spalla1-3, G. Gosso1-3, A.M. Marotta2, M. Roda1-2, F. Salvi4, M. Zucali1 1 Dipartimento di Scienze della Terra “ A. Desio” Sezione Geologia, Università degli Studi di Milano 2 Dipartimento di Scienze della Terra “ A. Desio” Sezione Geofisica, Università degli Studi di Milano 3 CNR-IDPA, Milano 4 ENI E&P Division, S. Donato Milanese

Nappe theory originated in the alpine foreland belt, but the structure and kinematics of the axial collision zone has been the intriguing problem of alpine tectonic studies from the early times. About a century ago separation of old continental rocks, recycled during superposed orogenic events, from Mesozoic oceanic rocks made clear the overall architecture of the suture zone between African and European margins; ductile low angle upthrusting was envisaged to have generated the thick pile of continental and oceanic sequences named Pennine nappe belt (Argand, 1911; Staub, 1917). Successively, addition of environmental details to fragments of Mesozoic sediments, stuck solution of the thickening kinematics upon its starting point of pre-orogenic paleogeograpy and this view generated virtual problems of lower crustal mass excess within the collisional mechanics, that last- ed till the sixties (Laubscher, 1971). Since the seventies, tectonothermal evidences from metamorphic rocks, displayed by estimates of petrogenetic conditions of mineral assemblages made subduction signatures evident (Ernst, 1971; Dal Piaz et al., 1972) and imposed lithosphere-scale thickening processes. Crustal location of pre-Alpine protoliths was revealed in many of the stacked continental and oceanic slices from polyphased pre-orogenic tectono-thermal imprints, together with signs of contrasting P-T regimes, related to Alpine collision, to pre-Alpine rifting or Variscan tectono-metamorphic episodes. Origin of the recumbent-like overthrust nappe finite architecture was made manifest as a long polyphase process generated at various crustal depths (Hall, 1972; Higgins, 1964; Milnes, 1978) and fossil mineral equilibria preserved in protected strain domains became the effective key to unravel repeated episodes of tectonic coupling and decoupling in the subduction-exhumation-collision- cycle (Spalla et al., 1996). During the last 20 years geologists, working in the axial part of the Alps, recognised that units contoured on the basis of their litho- stratigraphic similarities do not coincide with units sharing the same tectonic and metamorphic evolution. Actually subduction-collision zones are characterized by coupling and decoupling of lithos-

202 GNGTS 2009 SESSIONE 1.2 pheric slices, which work in competition building up the tectonic units of metamorphic belts (e.g. Polino et al., 1990; Chemenda et al., 1996; Stoeckhert & Gerya, 2005). During plate convergence, contours of these units are transient and can be investigated integrating structural and petrologic analysis. Structural and metamorphic evolutions of basement rocks, rather than purely lithologic associations, are tracers of their transit throughout different levels of the lithosphere and sublithos- pheric mantle. Individuation of contours of thermally-characterized and structurally distinct units (= tectono-metamorphic units = TMU; Spalla et al., 2005) is crucial to define the variation in size of such lithospheric slices, involved in the dynamic of an active margin: the fundamental tool is the reconstruction of quality P-T-d-t paths, implying exploitation of the full structural and metamorphic “rock memory”. Size definition of TMUs is critical to infer geological processes as tectonic erosion or accretion at the trench margins, continental collision or deep subduction of continental crust (ablative subduction) or exhumation velocity variation and its influence on rapid and effective meta- stabilisation of HP- and UHP-LT assemblages (e.g. Cloos 1993; England & Thompson 1984; Ernst 2001; Lallemand 1999; Tao & O’Connel 1992). The TMU investigation tool bears a marked thermo-tectonic connotation and offers possibilities to test by numerical modelling the physical com- patibilities of some interconnected variables (e.g. gravity, plasticity, heath transfer) with the interpretative geologic history. Comparison between modelling predictions and natural data obtained by this analytical approach (Marotta & Spalla, 2007; Spalla & Marotta, 2007; Meda et al., in press, Roda et al, this volume) helped to solve standing ambiguities on the pre-Alpine and Alpine geodynamic evolution of different continental units of Central and Western Alps and to explore the crustal level of protoliths derivation. Computer-aided 3D estimate of structurally and chemically “reactive” volumes (Salvi et al., in press) helps to evaluate their potential influence on the choice of the physical parameters for numerical modeling. References Argand E.; 1911 : Les Nappes de recouvrement des Alpes pennines et leurs prolongements structuraux. Mat. Carte Géol. Suisse 1-26. Chemenda, A.I., Mattauer, M., Bokun, A.N.; 1996: Continental Subduction and a mechanism for exhumation of highpressure metamorphic rocks: new modeling and field data from Oman, Earth Plan. Sci. Lett., 143, 173-182. Cloos M.; 1993: Lithospheric buoyancy and collisional orogenesis: subduction of oceanic plateaus, continental margins, island arcs, spreading ridges and seamounts. Geol. Soc. Am. Bull. 105, 715-737. Dal Piaz G.V., Hunziker J.C., Martinotti G.; 1972: La Zona Sesia - Lanzo e l’evoluzione tettonico-metamorfica delle Alpi Nordoccidentali interne. Mem. Soc. Geol. Ital. 11, 433-460. England P.C., Thompson A.B.; 1984: Pressure-Temperature-Time paths of regional metamorphism I. Heat transfer during the evolution of regions of thickened continental crust. Journ. Petrol. 25, 894-928. Ernst W.G.; 1971: Metamorphic zonations on presumably subducted lithospheric plates from Japan, California and the Alps. Contrib. Miner. Petrol. 34, 43-59. Ernst W.G.; 2001: Subduction, ultahigh-pressure metamorphism and regurgitation of buoyant crustal slices - implications for arcs and continental growth. Phys. Earth Planet. Int., 127, 253-275. Hall W.D.M.; 1972: The structural and metramorophic history of the lower pennine nappes, Valle di Bosco, Ticino, Switzerland. PhD, Imperial Coll. London. Higgins A.K.; 1964: The structural and metamorphic geology of the area between Nufenenpass and Basodino, Tessin, Switzerland. PhD, Imperial Coll. London. Lallemand S.; 1999: La subduction océanique, Gordon and Breach Science Publishers, 194. Laubscher H.P.; 1971: The large scale kinematics of the Western Alps and the Northern Apennines and its palinspastic implications. Am. J. Sci. 271, 193-226. Marotta A.M., Spalla M.I.; 2007: Permian-Triassic high thermal regime in the Alps: Result of late Variscan collapse or continental rifting? Validation by numerical modeling. Tectonics. 26, doi:10.1029/2006TC002047. Meda M., Marotta A.M., Spalla M.I. (in press): The role of mantle hydration into the continental crust recycling in the wedge region. Geol. Soc. London Spec. Pub. Milnes A.G.; 1978: Structural zones and continental collision, Central Alps. Tectonophysics. 47, 369-392. Polino, R., Dal Piaz, G. V., Gosso, G.; 1990: Tectonic erosion at the Adria margin and accretionary processes for the Cretaceous orogeny of the Alps. Mem. Soc. géol. France, NS 156, 345-367. Roda M., Marotta A.M., Spalla M.I.; 2009: Numerical simulation of ocean/continent convergent systems: influence of subduction geometry and mantle wedge hydration on crustal recycling. This volume. Salvi F., Spalla M.I., Zucali M., Gosso G. (in press): 3D-evaluation of fabric evolution and metamorphic reaction progress in polycyclic and polymetamorphic terrains: a case from the Central Italian Alps. Geol. Soc. London Spec. Pub.

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Spalla, M. I., Marotta, A. M.; 2007: P-T evolutions vs. numerical modelling: a key to unravel the Paleozoic to early-Mesozoic tectonic evolution of the Alpine area. Periodico di Mineralogia, 76, 267-308. Spalla M.I., Zucali M., Di Paola S., Gosso G.; 2005: A critical assessment of the tectono-thermal memory of rocks and definition of tectono-metamorphic units: evidence from fabric and degree of metamorphic transformations. Geol. Soc. London Spec. Pub., 243, 227-247. Spalla M.I., Lardeaux J.M., Dal Piaz G.V., Gosso G., Messiga B.; 1996: Tectonic significance of alpine eclogites. J. Geodyn., 21, 257-285. Staub R.; 1917: Ueber Faziesverteilung und Orogenese in den Suedoestlichen Schweizeralpen. Beitr. Geol. Karte Schweiz., 46, 165-198. Stoeckhert, B., Gerya, T.; 2005: Pre-collisional high pressure metamorphism and nappe tectonics at active continental margins: a numerical simulation. Terra Nova, 17,102–110. Tao W.C., O’Connel R.J.; 1992: Ablative subduction: a two-sided alternative to the conventional subduction model. J. Geophys. Res., 97, 8877-8904.

BLOCK-MODEL VERSUS THERMO-MECHANICAL MODEL: NEW INSIGHTS ON THE PRESENT-DAY REGIONAL DEFORMATION IN THE SURROUNDINGS OF THE CALABRIAN ARC R. Splendore, A.M. Marotta Dipartimento di Scienze della Terra, Sezione di Geofisica, Università degli Studi di Milano

A finite element thermo-mechanical modeling is used to analysis the present-day crustal deformation in the surroundings of the Calabrian Arc. The major structural complexities of the Tyrrhenian area, such as the rheological heterogeneities resulting from a thermal analysis, are taken into account. Tectonic deformation in Central Mediterranean is obtained by using a 2D finite elements model, based on the spherical thin sheet approach developed by Marotta et al. (2004). Boundary conditions are expressed in terms of velocities and, with the exception of the southern boundary of the model, they are the same as for the best fit model of Marotta et al., 2004. Along the southern boundary of the model account for Africa-Eurasia relative motion based on ITRF2005 (Altamini et al., 2007) and are calculated following the procedure in Nocquet et al. (2001) to estimate the Eulerian Pole. Thermal Analysis is based on a 3D numerical model performed in the sole Central Mediterranean on a 3D grid, composed by prismatic elements obtained by projecting along the depth the 2D numerical grid used in the tectonic model. At the upper boundary of the model temperature is fixed to 300 K. At the lower boundary of the model, heat flow coincides with the residual heat flow qr derived from the observed surface heat flow qs (Pollack et al., 1993, augment- ed by Artemieva (2006)’s data). Our analysis indicates smooth variations characterizing the depth of the base of the lithosphere, with an average lithospheric thickness (neglecting the topography) ranging between 70 and 90 km, and strongest gradients occurring south of the Calabrian arc, in proximity of the trench associated to the Calabrian subduction, where thermal doubling occurs within 500 km. The predicted 3D lithosphere thermal field is used to determine the strength of the lithosphere in the Mediterranean region. Lithosphere strength is calculated by assuming that rocks behave like a brittle or a ductile material according to their composition and thermal state. For the ductile behavior, dry felsic granulite is assumed for the crust and dry dunite is assumed for lithospheric and sub-lithospheric mantle. Our results show that a strong lithosphere paves the Tyrrhenian, with a crust strongly coupled with mantle below the Provencal Basin and the Calabrian Arc surroundings, while the concurrence of hot lithosphere and thick crust in the Pannonian Area drives an average soft lithosphere. Furthermore, the southern portion of the Adria microplate can be rheologically differentiated from the northern portion, with the northern block stiffer of about half order of magnitude then the southern one. Once the predicted lithosphere stiffness is accounted within a tectonic model, the results confirm the crucial role played by the lateral rheological heterogeneities when deformation is ana-

204 GNGTS 2009 SESSIONE 1.2 lyzed at the short wavelengths of few hundreds of kilometres. In fact, the strong rheological gradients concur with crustal and lithosphere thickness variations to drive a diffuse SW-NE extension within the regional context of active Africa-Eurasia convergence. In particular, tectonic model accounting for sole 50% of Africa-Eurasia convergence transmitted through the Calabrian Subduction zone, predicts extension in the Sicily, southern Calabria and part of the southern Tyrrhenian, and compression in the Algerian region. References Altamimi, Z., Collilieux, X., Legrand, J., Garayt, B., & Boucher, C. ; 2007. ITRF2005: A new release of the International Terrestrial Reference Frame based on time series of station positions and Earth Orientation Parameters, Journal of Geophysical Research, 112, B09401, doi:10.1029/2007JB004949. Artemieva, I. M.; 2006. Global 1°x1° thermal model Tc1 for the continental lithosphere: implications for lithosphere secular evolution. Tectonophysics, 416, 245-277. Marotta, A. M. & Sabadini, R.; 2008. Africa-Eurasia kinematics control of long-wavelength tectonic deformation in the Central Mediterranean. Geophysical Journal International, 175, 742-754. Marotta, A. M., Mitrovica, J. X., Sabadini, R. & Milne, G.; 2004. Combined effects of tectonics and glacial isostatic adjustment on intraplate deformation in central and northern Europe: Applications to geodetic baseline analyses. Journal of Geophysical Research, 109, B01413, doi:10.1029/2002JB002337. Nocquet, J. M., Calais, E., Altamini, A., Sillard, P., Boucher, C. ; 2001. Intraplate deformation in western Europe deduced from an analysis of the International Terrestrial Reference Frame 1997 (ITRF97) velocity field. Journal of Geophysical Research, 106 (B6), 11239-11257. Pollack, H. N., Hurter, S. & Johnson, J. R.; 1993. Heat Flow from the Earth’s interior: analysis of the global data set. Reviews of Geophysics., 31 (3), 267-280.

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