IstitutoIstituto NazionaleNazionale Helmholtz-ZentrumHelmholtz-Zentrum PPotsdamotsdam- didi GeofisicaGeofisica e VulcanologiaVulcanologia DDeutscheseutsches GeoForschungsZentrumGeoForschungsZentrum RECENTRECENT TTECTONICECTONIC SSTRESSTRESS FFIELDIELD SSTATETATE IINN IITALYTALY FFROMROM NNUMERICALUMERICAL MMODELLINGODELLING AANALYSISNALYSIS ()(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 33a.a. 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. 66)). The mean SH mechanisms, overcoring and recent slip of faults (Fig.(Fig. 22a)a). 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 33bb 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 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. 22a)a) complex tectonic setting of these areas (Fig.(Fig. 4a,b,c,d)4a,b,c,d). The FiguresFigures 44a-da-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 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 (Fig.Fig. 2b2b) and it is prevalent along the Apenninic belt and in the west- 3 E l 1 (2008) World Stress Map Switzerland recently seismicity. 3 o Volcanoes ern part of Alps (Fig.(Fig. 22a)a). 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. 22aa aandnd bb)) figurefigure 22bb 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 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 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 -Linosa-Malta rift use 600 data of SH records from the World Stress Map database re- solutions 45˚ Austria 450 40° 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. 11).). 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 IONEAN SEA Palermo g 0 km 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. indicators E Smoothing Algeria c)c) MEDITERRANEAN SEA EU Malta island Mt. Etna FigureFigure 1 35˚ The database has been split in two subsets: I) breakouts, faults and overcorings and II) focal mechanism solutions . The smoothing nonian (Fig.(Fig. 5a)5a) (Fig.(Fig. 5b)5b) Alps AD Pan map of shallower data reflects the local trend (low wave-lenght= blue color) but the smoothing map of focal mechanism solutions shows some area with Pantelleria island a higher wave-length (orange to red shade colors). This result might be explained by an upper part of crust mostly influenced by accommodation of SMOOTHINGSMOOTHING MMETHODETHOD sedimentary layers and by local perturbation (e.g. topography effect) than the underlying strata. The shallower block is controlled by the skin tectonics Tunisia LEGEND Dina A lot of smoothing methods exist to understand which principal stress pattern governs in the area, to Algeria while deeper one by force of plate tectonics . Malta island rid Mountain belts related to (Fig.(Fig. 5c)5c) es continental collision remove the local perturbations and to predict a stress field orientations also in the regions which lack Fold-and-thrust belts related 5° 7.5° 10° 12.5° 15° 17.5° 20° 5° 7.5° 10° 12.5° 15° 17.5° 20° 0 100 km Adri to the backarc opening data records (Hansen and Mount, 1990; Coblentz et al., 1998; Bird et al., 2006; Müller et al., 1997; Apennine 47.5° Accretional complexes related 47.5° atic Tingay et al., 2005, 2006; Heidbach et al., 2010). In this paper the authors apply the Heidbach et al.’s 35˚ to the oceanic subduction SH orientation above salt

Balearic Intracontinental belts smoothing method (2010) which is an improvement of Müller et al., 1997 method. It consists of two Km 7 s Backarc basin steps: GP The present-day stress data records of the Po Plain and the Emilia-Romagna arc exhibit a constant NE-SW compression

Residual Tethyan ocean 5 45° 45° salt pillow regime with small rotations of the SH caused by local structural features (Montone and Mariucci, 1999; Pierdominici et al.,

Lithospheric buckling CS AP I Step II Step 2005; Carminati et al., 2010; Carminati and Vadacca, 2010). The present-day stress data records of the Calabrian arc and Main compressive faults Tyrrhenian e of Sicily area are more scattered, underlying the tectonic complexity of the region. Indeed, the rotations of the compres- Setting: Setting: SH orientation Main extensive faults below salt 42.5° sional axis are due to the presence of active structural faults (e.g. the SH orientated WNW-ESE in the Hyblean region in - 0.2 regular grid - data number threshold (=10); r 42.5° Main strike-slip faults c)c) agreement with tectonic structures) and rift zones (Eolian islands and Mt. Etna volcano; Catalano et al., 2010). AI Direction of maximum - weight factor to each data quality: - variance threshold (≤ 25°) m u 13 km 10 k extension Algerian Cal. Arc A= 1/15; B=1/20 and C=1/25 - rad_min= the smallest search radius SC ET REFERENCESREFERENCES SI Direction of maximum Amato and Montone, 1997 - Geophys. J. Int., 130, 519-534; Anderson and Jackson, 1987 - Geophys. J.R. Astron. Soc., 91, 937-987 - srad_range (e.g. 50 to 1000 km) (=50km or 100km). g 40° 40° IP compression Legend Barba et al., 2010 - Tectonophysics, 482 (1-4), 193-204; Bird et al., 2006 - J. Geophys. Res., 111 (B08402). doi:10.1029/2005JB003882 Bressan et al., 2003 - Bull. Seism. Soc. Am., 93, 1280-1297; Calais et al., 2003 - Earth Plan. Sci. Lett., 216, 8–92 - dist_weight _threshold: 10 - dr_max= maximum ratio of mean i Quaternary Middle Jurassic Carminati and Vadacca, 2010 - JGR, doi:10.1029/2010JB007870 in press; Carminati et al., 2010 - JGR, 115, B02401, doi:10.1029/2009JB006395 SP distance and search radius (=1.0) Catalano et al., 2010 - Tectonophysics, 486, 1-14; Coblentz et al., 1998 - J. Geophys. Res., 103 (B1), 919–931 AF nnel Sicily Cha Figure 5F Upper Creataceous Lower Jurassic DeMets et al., 1994 - Geophys. Res. Lett., 21, 2191–2194; Devoti et al., 2008 - Earth Plan. Sci. Lett., 273, 163–174 ME 37.5° Dewey et al., 1973 - Bull. Soc. Am. Bull., 84, 3137–3180; Dewey et al., 1989 - Alpine Tectonics, 45, 265–283 TA Result: 37.5° Lower Creataceous Evaporites Triassic PP Result: Heidbach et al., 2010 - Tectonophysics, 482, 3-15; Hansen and Mount, 1990 - J. Geophys. Res., 95 (B2), 1155–1165 - mean SH orientation Upper Jurassic Basement http://www.bo.ingv.it/RCMT/searchRCMT.html; Mariucci et al., 2010 - Geophys. J. Int., 182, 1096-1102 - mean SH orientation Montone and Mariucci, 1999 - J. Geodynamics, 28, 251-265; Montone et al., 2004 - J. Geophys. Res., 109, doi:10.1029/2003JB002703 SC: Sardinia Channel; ME: Malta Escarpment; SI: Sicily; SP: Sicily Plate; IP: - variance of the mean SH orientation Müller et al., 1997 - Tectonophysics 275, 199–219; Patacca and Scandone, 1989 - Accad. Naz. dei Lincei, pp. 157-176, Rome, Italy a)a) b)b) Perniola et al., 2004 - Geophys. J. Int., 156, 297–306; Pierdominici et al., 2005 - Annals of Geophysics, 48 (6), 867-881 - wave-length of the stress pattern in 35° 35° Ionian Plate; AI: ; ET: Mount Etna; PP: Pelagian Plateau; CS: - number of the four quadrants of the search circle Pondrelli et al., 1995 - Geophys. J. Int., 122, 938-952; Slejko et al., 1999 - Bull. seism. Soc. Am., 89, 1037–1052 search radius r [km] [km] Corsica-Sardinia block; AP: Apulian block; GP: Gargano Promontory; AD: Adri- terms of maximum search radius max search radius rmax Sue et al., 1999 - J. Geophys. Res., 104, B11, 25611-25622 ; Tingay et al., 2005 - Lead. Edge, 24 (12), 1276–1282 atic plate; EU: Eurasian plate; AF: Africa plate; TA: Tunisian Atlas - mean distance of these data records to the grid point 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 100 150 200 250 300 350 400 450 500 550 600 650 700 750 Viganò et al., 2008 - Tectonophysics, 460, 106/115; Westaway, 1992 - J. Geophys. Res., 97, 15437-15464