GNGTS 2019 - Atti del 38° Convegno Nazionale

GNGTS 2019 S essione 3.1 579 - the normal Quaternary active faults that ruptured the surface during the August 24 (M w =6.0) and October 30 (M w =6.5), 2016 strong earthquakes in the Mt. Vettore-Mt. Bove areas, in central Italy Apennines (Chiaraluce et al. , 2017). Our multi-parametric investigation (Luiso et al. , 2018) depicted the NW–SE Mt. Vettore-Mt. Bove fault system dipping 60°–70° westward. We also detected the splays of this primary fault system and its blind antithetic NW–SE structure, dipping northeastward. In the Norcia basin, we highlight two main faults bordering the basin with a dip of about 45°. The one edging the eastern side dips westward, whereas the fault edging the western side dips eastward. Thanks to our analysis we could identify and characterize the geometry of the Norcia and Vettore master faults, as well as other blind/buried and/or silent faults that are related to the 2016 seismogenic structure; - the Paganica fault, which bounds to the northeast the Aterno River valley, in the central Italy Appennines chain, causing the 2009 seismic sequence (mainshock: April 6, 2009 M w =6.1). Prior to the 2009 earthquake, the geometry and activity of this fault was only roughly known. There is a general discrepancy between the length of the seismologic– geodetic modelled fault (up to 18 km), the limited size of the primary continuous coseismic surface ruptures (3 km), and the significant morphological expression of the nearby Paganica-San Demetrio normal fault (Emergeo Working Group, 2010; Pucci et al. , 2015). This raised a debate about the maximum rupture length of the Paganica fault and its capability to generate earthquakes stronger than the 2009 main shock. Our multi parametric investigation highlights a continuous MDA maximum coinciding with the epicentral distribution along the Aterno basin. This suggests the existence of a buried fault much larger than what it can be inferred from the surface breaks. Moreover, the results of the DEXP analysis on gravity data characterized the geometry of the SW 45° dipping Paganica fault plain in good agreement with the hypocentral distribution; - the eastern Molise area (San Giuliano di Puglia, SouthernApennines) hit by the 2002-2003 seismic sequences (Mw max = 5.8 on October 31, 2002). The area, struck by this sequence, falls between the Apennines axial zone and the Apulia-Gargano foreland, a region where, based on historical and instrumental seismicity, no comparable earthquakes occurred in the last 1000 years (Valensise et al. , 2004). The aftershocks alignment (Chiarabba et al. , 2005; Chiarabba et al. , 2014) suggests that the rupture occurred on an EW plane of focal solution, with a dextral fault motion. Our analysis (Luiso et al. , 2016) highlighted a good correlation between the E-W re-localized San Giuliano di Puglia earthquake seismic sequence and a MDA maximum with E-W direction, but no evidence of E-W surface mapped faults. This suggests that this is a buried fault. Furthermore, this correlation may suggest that the E-W MDA lineament is the westward continuation of the Mattinata Fault , located in the Gargano Promontory and interrupted by clear MDA lineaments with Apenninic direction related to low-angle thrusts. The hypocentral section shows a sub- vertical plane, with the aftershocks clustering between 7 and 18 km depth well-correlated with the sub-vertical DEXP maxima. Based on the good results obtained, a multiparametric study of three other areas of the Abruzzo-Molise region, of high seismotectonic interest, is in progress: in the south-western sector of Mt. Matese, the Fucino basin and the Sulmona basin (Fig. 2). The Abruzzo and Molise regions (Central-Southern Apennines) are two of the most active areas from a geodynamic point of view of the Italian Apennines, characterized by the occurrence of intense and widely spread historical and recent seismic activity. Most seismicity of the area is concentrated along the chain. The Matese area was hit by a seismic sequence (Mw max = 5.1 on December 29, 2013) in 2013-2014. Our approach shows a strong correlation among faults (Boncio et al. , 2016), the location of the 2013-2014 Matese seismic sequence (M w =5.0) (Ferranti et al. , 2015) and MDA lineaments from gravity data (Fig. 2).