Abstracta B S T R a C T Recent Tectonic Stress Field State
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IstitutoIstituto NazionaleNazionale Helmholtz-ZentrumHelmholtz-Zentrum PPotsdamotsdam- didi GeofisicaGeofisica e VulcanologiaVulcanologia DDeutscheseutsches GGeoForschungsZentrumeoForschungsZentrum RECENTRECENT TTECTONICECTONIC SSTRESSTRESS FFIELDIELD SSTATETATE IINN IITALYTALY FFROMROM NNUMERICALUMERICAL MMODELLINGODELLING AANALYSISNALYSIS (Italy)(Italy) (Germany)(Germany) T21B-2156T21B-2156 SimonaSimona PierdominiciPierdominici1 aandnd OOliverliver HHeidbacheidbach2 1.1. SismologiaSismologia e Tettonofisica,Tettonofisica, INGV,INGV, Rome,Rome, ItalyItaly 2.2. SeismicSeismic HazardHazard andand StressStress Field,Field, GFZGFZ GermanGerman ResearchResearch CentreCentre forfor GeosciencGeosciencees,s, PPotsdam,otsdam, GGermanyermany [email protected];[email protected]; [email protected]@gfz-potsdam.de ABSTRACTABSTRACT THETHE IITALIANTALIAN SSTRESSTRESS DDATABASEATABASE SMOOTHINGSMOOTHING MMAPSAPS DISCUSSIONDISCUSSION We examine the contemporary stress in Italy studying the present-day The tectonic stress of Italy is inferred and well defined by borehole breakouts, earthquake focal The result of the smoothing analysis (black bars) is shown in the figurefigure 3a.3a. The SH orientations and color-code rmax values are displayed. The blue and The smoothed SH orientation shows a trend that reflects the structural setting in the study area (Fig.(Fig. 6)6). The mean SH mechanisms, overcoring and recent slip of faults (Fig.(Fig. 2a)2a). In addition to the dataset published by yellow colors indicate that the area is characterized by a stress pattern from regional to local wave-lenght (rmax<400km) while the orange-brown colors orientation is well constrained along the Apenninic belt (NW-SE) and its orientation corresponds with one of the normal maximum horizontal stress orientation to characterize the relationship active faults. The eastern part of the Alpine arc with a NNW-SSE-orientation of SH due to the active thrusts in this area. Heidbach et al., 2010, more than 100 stress data records have been added (Barba et al., 2010, Mari- indicate a regional stress pattern (rmax>400km). The figurefigure 3b3b represents the variance of the single SH orientations. The area with lowest variance The compression has moved from Dinarides to the Friuli and Southalpine, as deduced from focal mechanism of the major between active stress, past tectonic setting and the seismicity. The ucci et al., 2010 and http://www.bo.ingv.it/RCMT/searchRCMT.html). The data density is high for all (green color) is located along the Apennines belt while the high values (red color) are present in four zones. The high variance is probably due to the Italy, except for Sardinia island and southern Apulia region where little data are present . events (Slejko et al., 1999; Bressan et al., 2003; Perniola et al., 2004; Viganò et al., 2008). The western part of the Alps geodynamic setting of Italy is particularly complex. Italy is involved in (Fig.(Fig. 2a)2a) complex tectonic setting of these areas (Fig.(Fig. 4a,b,c,d)4a,b,c,d). The FiguresFigures 4a-d4a-d show the correlation among the smoothing value of SHmax orientation, shows a less defined distribution of the SH orientation with rotations, probably related to the bent of the thrusts (active in The earthquake mechanism solutions are most concentrated along the Apenninic belt and active tec- contemporary stress data records and tectonics. the N-S convergence of Africa and Eurasian plates and currently un- tonic regions (the far western and eastern part of the Alpine chain and along the subduction zone) the outboard of the thrusts) and to the coexistence of a widespread extension in the core of the western Alps revealed by 5° 7.5° 10° 12.5° 15° 17.5° 20° 5° 7.5° 10° 12.5° 15°17.5° 20° earthquake analysis (Sue et al., 1999). while the borehole breakout records are located on correspondence with gas and/or oil reservoirs Germany Germany Method: dergoing NE-SW extension perpendicular to the Apenninic fold and Austria Austria focal mechanism (particularly in the Po Plain, Adriatic and Sicilian off-shore areas, southern Apenninic foredeep and 47.5° Slovakia 47.5° Slovakia breakouts drill. induced frac. within of some intramountain basins). The active faults (Late Quaternary-Holocene) are located along overcoring thrust belt and with the opening of the Tyrrhenian basin (Late Torto- Switzerland Switzerland hydro. fractures 5˚ 10˚15˚ 20˚ geol. indicators the Apenninic belt and the overcoring data are mainly distributed on the Alpine belt, some in Sicily and Regime: nian). This process happens in the presence of still active subduction NF SS TF U Slovenia Slovenia in offshore Sicily. Quality: N Germany Thrust faults Milano Milano A From regions aforementioned, three regimes are still active. The normal faulting regime is inferred Croazia Venezia Croazia Normal faults system extending from Sicily to northern Apennines, as confirmed by B Austria France France C 45° 45° D S Strike-slip faults from focal mechanism solutions ( ) and it is prevalent along the Apenninic belt and in the west- 3 Fig.Fig. 2b2b E Switzerland l recently seismicity. 1 (2008) World Stress Map o Volcanoes 3 ern part of Alps (Fig.(Fig. 2a)2a). On the contrary, the eastern part of the Alpine chain, the foredeep and fore- Bosnia Bosnia v Intrusiv bodies and and a Ancona Herzigovina Ancona Herzigovina This tectonic setting with highly variable plate boundary events and land Apenninic belt and the northern part of Sicily are characterized by thrust faulting particularly from e Serbia k Base of Pliocene-Quaternary 2 Serbia i a isobaths focal mechanism solutions but not only . In , only 92 data show a strike-slip r Elba island body forces induced by topography results in an inhomogeneous (Fig.(Fig. 2a2a andand bb)) figurefigure 2b2b Montenegro Montenegro Smoothing ADR Tus ADR cani 42.5° 42.5° an a IAT rchipe IAT regime located close to Ancona town and to south-eastern part of Italy (Molise-Apulia area; ). IC SEA lag IC S Direction of maximum Fig.Fig. 2a2a Corsica Corsica o u Tremiti islands EA stress pattern. Here we quantify the spatial changes of the wave- Rome Rome Slovenia extension along the Maddalena Milano Siculo-Calabria rift zone archipelago g Albania Albania Asinara 5˚ 10˚ 15˚ 20˚ island Pon length of the stress pattern by a statistical analysis. As input data we tin Vesuvio Direction of maximum o archi Croazia pel volcano Venezia ago France Brindisi Ischia Brindisi i extension along the 483 island 100% Sardinia Sardinia Capri Germany N Focal mechanism island Pantelleria-Linosa-Malta rift use 600 data of SH records from the World Stress Map database re- solutions 45˚ Austria 450 40° TYRRHENIAN SEA 40° TYRRHENIAN SEA a)a) Figure 3F b)b) Faults Direction of Nubia-Eurasia O vercorings IONEAN SEA IONEAN SEA lease 2008 and about 100 new data records. The result of this statisti- Switzerland S. Pietro convergence 400 island 4 Slovakia Cagliari Cagliari 80% S. Antioco island Eolie islands cal analysis is a mean orientation of the maximum horizontal compres- 350 Palermo Palermo Slovenia RSM Bosnia MEDITERRANEAN SEA MEDITERRANEAN SEA Egadi islands Serbia Milano Etna volcano Number ofdata and sional stress SH on a 0.1° grid and the maximum smoothing radius for 300 37.5° 37.5° Ancona France Venezia Croazia 60% Herzigovina 45˚ 250 Pantelleria island which the standard deviation of the mean SH orientation is less than Bosnia and Tunisia Tunisia Algeria Algeria 6 Elba island Herzigovina 200 Malta island Montenegro 25°. This latter is the wave-length of the stress pattern and reveals for RSM 40% Serbia Cumulative data a)a) b)b) Ancona Tus 35° 35° canian ADR 150 archip Italy that the entire region has wave-length less than 200 km for Italy. variance elag IATI search radius r [km] e Corsica o max < 25 25-40 > 40 C SEA Data Quality Elba island Montenegro 20% 100 Tremiti islands 100 150 200 250 300 350 400 450 500 550 600 650 r Rome A BCDE Tus ADR can ian A ar chi IATIC S pel Overcoring Corsica ago 50 l Tremiti islands EA Maddalena Rome N u archipelago Breakout A 0 50 km b Maddalena l archipelago 0% 0 Asinara a TECTONICSTECTONICS OOFF IITALYTALY Earthquake b 4 a)a) b)b) NF TF SS U g island Asinara a Vesuvio n island Fault Vesuvio n Pontino Pont volcano The geological and structural setting of Italy is complex The area is in- ino volcano Kind of regime arch archip ipe i (Fig.(Fig. 1).1). TYRRHENIAN SEA elago i TYRRHENIAN SEA lago Ischia Brindisi i island Ischia Brindisi Stress regime Capri a RSM island island Capri a island volved in the N-S convergence of the Africa and Eurasia plates, which was es- extensional e compressive N strike-slip 40˚ Figure 6F RSM tablished in Late Creataceous and is still ongoing even if more slowly (Dewey et unknown r 0 50 km 40˚ S. Pietro IONEAN SEA al., 1973 and 1989; DeMets et al., 1994; Calais et al., 2003; Devoti et al., 2008). island Cagliari u S. Antioco Eolie The present-day stress in Italy is characterized by a NE-SW extension perpen- island islands N MEDITERRANEAN SEA S. Pietro 50 km IONEAN SEA Palermo g 0 island dicular to the Apenninic fold and thrust belt (Anderson and Jackson, 1987; West- Egadi islands Cagliari Mt. Etna N i S. Antioco NF SS TF U Thrust faults Direction of maximum Eolie away, 1992; Pondrelli et al., 1995; Amato and Montone, 1997), coeval with the extension along the island islands Normal faults FigureFigure 2 focal mechanism Quality: Strike-slip faults Siculo-Calabria rift zone 0 50 km breakouts Direction of maximum Pantelleria island A Volcanoes opening of the Tyrrhenian basin (Late Tortonian; Patacca and Scandone, 1989). Figure 4F drill. induced frac. extension along the d)d) B Intrusiv bodies Pantelleria-Linosa-Malta rift overcoring C Base of Pliocene-Quaternary Direction of Nubia-Eurasia Palermo hydro. fractures D isobaths convergence Egadi islands Tunisia geol.