GNGTS 2017 - 36° Convegno Nazionale

GNGTS 2017 S essione 1.2 155 kinematics of normal faulting earthquakes in the axial part of southern Italy. Extensional earthquakes are located in the Apulian platform and probably reactivate existing faults that had an earlier (Early Pleistocene) and more significant history of transtension, as shown by our analysis of fault-slip lineations on outcropping faults. Thus, as documented elsewhere in the Apennines, active extension may be a young feature. Strikingly, extensional seismicity abruptly ends where the normal faulting documented in the geological record terminate at the northeastern border of the Mercure Basin and is replaced by reverse and transpressional tectonics. In this latter area, intermediate (~9-17 km) depth strike- slip and locally reverse-oblique seismicity are observed prevalently in the Apulia middle crust. These earthquakes distribute along an ~ESE-WNW trending band and are characterized by NE-SW trending P-axes. Because these observations are at odds with the regional kinematics of strike-slip earthquakes in the eastern part of southern Italy, which have NW-SE trending P- axes, we argue that seismicity here is controlled by inherited mechanical anisotropies. These latter are represented by high-angle faults which acted as reverse during the contractional uplift of the Apulian unit beneath the southern Apennines. Unlike other strike-slip earthquakes in the eastern part of southern Italy, which are located in the Apulia unit underthrusting the Apennines orogen, the intermediate events studied here are found in the Apulia unit involved in contractional uplift. We propose that this departure from the regional pattern is controlled by the local anisotropy represented by an ~ESE-WNW trending deformation belt. This belt could be part of a regional deep crustal to lithospheric boundary stretching from the Tyrrhenian to the Ionian coast and separating the Southern Apennines from the Calabrian Arc. Deeper (~17-23 km) strike-slip earthquakes differ with respect to intermediate depth strike- slip earthquakes because they have P-axis with a NW-SE trend, more akin to the regional strike- slip seismotectonics of eastern part of southern Italy. These deep earthquakes are found beneath and west of the extensional domain, and are conceivably located in the Tyrrhenian lower crust wedged between the Apennines and underlying Apulia foreland. Alternatively, because of the uncertainty in the reconstruction of the structural model, they could fall in the latter domain, where they would document tearing of the subducted Ionian-Adriatic plate. The deep strike-slip events conform to the regional kinematics, suggesting that they are controlled by the large-scale Adria-Europe plate interaction. Depth of the brittle-ductile transition in the Gargano area (Italy) inferred from a thermo-rheological model M. Filippucci 1 , A. Tallarico 1 , M. Dragoni 2 , S. de Lorenzo 1 1 Dipartimento di Scienze della Terra e Geoambientali, Università degli Studi “Aldo Moro”, Bari, Italy 2 Dipartimento di Fisica e Astronomia, Alma Mater Studiorum, Università di Bologna, Italy The mountainous promontory of Gargano is, from a structural point of view, part of the Apulia foreland that protudes into the southern Adriatic sea (Fig. 1). The promontory and its surrounding area are subjected to a frequent seismic activity although they lie out of the Apennine axis, which is the main Italian seismogenic area (Milano et al. , 2005). In fact, at least 11 events, having an estimated M W >5.5, struck the Gargano and neighboring areas in the past (Del Gaudio et al. , 2007). Nevertheless, the present understanding of the regional tectonics is considered incomplete (Camassi et al. , 2008), as demonstrated by the M w =5.8) Molise earthquake in 2002 (CPTI Working Group, 2004), of magnitude greater than it would be expected from the seismological knowledge of the region available at the time.