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 con- vergence, it is generally accepted that Adria played an important part in the frame of the subduc- tion/collision process of the region. However, a deep knowledge of its internal lithospheric struc- ture 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 teleseis- mic 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 verti- cal 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 direct- ly above or very close to the Adria plate. We consider 28 stations of the INGV National Seismic Network from the Apulia south- ernmost 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 proce- dure recently developed by Piana Agostinetti and Malinverno (2009). This innovative tech- nique permits to retrieve the Vs model beneath a seismic station without giving a priori con- straints 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 interest- ing and original features. In this talk we show some preliminary results on selected Adriatic sta- tions. As an example, we show in Fig. 1 – Moho depth in Italy from teleseismic receiver functions (from Piana Agostinetti and Amato, 2009). 139 GNGTS 2009 SESSIONE 1.2 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 vol- cano, at depth ranging between 10 and 20 km, along two tectonic structures (NE-SW and NNW-SSE) usually associ- ated with deeper magmatic recharge mechanisms (Figs. 1, 2). Afterwards, the seismicity was located along the shal- lower 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. 140 GNGTS 2009 SESSIONE 1.2 Fig. 2 - Time-Depth distribution of the analyzed seismicity. In order to provide seismologi- cal constraints to the magmatic unrest of the volcano, 336 earth- quakes 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 struc- ture 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 previou- sly 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 nor- thern 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 struc- tural system, however, has never been documented. This contribution aims at describing the defor- mation 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 bet- ween 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 deforma- tion is expressed in a more complex pattern, already close to the coastline. 141 GNGTS 2009 SESSIONE 1.2 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.