GNGTS 2016 - Atti del 35° Convegno Nazionale

406 GNGTS 2016 S essione 2.2 of L’Aquila breccia (CMA) laying upon 200-300 m thick of fluvial pelite and sand pertaining to Middle Pleistocene Fosso Genzano Synthem (FGS) and early Pleistocene Madonna della Strada Synthem (MDS) (Nocentini, 2016). In the two zones, Late Pleistocene terra rossa (TRS Synthem) mantles the epikarst developed onto L’Aquila breccia (CMA Synthem) (Tallini et al. , 2016a). Furthermore, the Quaternary cover lays upon Meso-Cenozoic limestones (Fig. 1). The geological model with the two different zones is in agreement with the results of the microtremor array measurements obtained by Di Giulio et al. (2014), which evidenced two distinct Vs vs depth profiles for the two zones (see Fig. 7 in Di Giulio et al. , 2014). The southern zone (i.e. SSPF hangingwall) shows the well-known Vs vs depth profile of L’Aquila (Del Monaco et al. , 2013) characterized by the Vs inversion due to L’Aquila breccia – pelite boundary and the sharp velocity increase caused by the superimposition of the pelite and sand onto the carbonate bedrock. The northern zone (i.e. SSPF footwall) does not show this Vs vs depth trend evidencing on the contrary higher Vs values caused by the shallower presence of the carbonate bedrock. The Vs vs depth profile of the northern zone, reported in Fig. 7a in Di Giulio et al. (2014), evidences also at 550 m below ground level a sharp Vs increase (from 1500 to 2500 m/s) which can be hypothetically caused by the superposition in the Meso-Cenozoic bedrock of the Messinian terrigenous foredeep units onto the Miocene ramp carbonate units (CRP). Supporting this hypothesis, field data show in the eastern part of L’Aquila town the presence of a thrust which causes the overlaying of slope to basin carbonate units (SLB) onto the Messinian terrigenous foredeep units (SYN) (Nocentini, 2016) as reported in the cross section of Fig. 1. The tectonic setting of the Pettino Fault System in L’Aquila town. The Pettino Fault System is composed by almost two main faults (the Pettino Fault and the Synthetic Splay of the Pettino Fault – SSPF) (Fig. 1) (Tallini et al. , 2012). They are sub-parallel, NW-SE oriented and SW dipping. Roughly SSPF can be considered a synthetic splay of the Pettino Fault. According to Tallini et al. (2012) we can conjecture a faulting rejuvenation, from the SSPF toward the Pettino Fault, this latter showing several evidences of active faulting (i.e. truncation of the Holocene debris cones apices located in the hangingwall of the Pettino Fault) (Galli et al. , 2011). In L’Aquila town we can hypothesize also a fault displacement transfer from the Pettino Fault to the Synthetic Splay of Pettino Fault (SSPF) and the fault displacement of Pettino Fault and SSPF is around 30 m and 300 m, respectively. The SSPF slip rate can be estimated around 0.2 mm/yr considering a fault displacement around 300 m and a Calabrian age for the Madonna della Strada Synthem (i.e. 1.5 Ma). This value is quite in agreement with the slip rates of others Quaternary faults in central Italy (Galli Fig. 1 – Cross section of L’Aquila town (from Nocentini, 2016 and Nocentini et al. , 2016). COL: colluvium deposit (Holocene); ATF: fluvial and alluvial fan deposits (Holocene); CPB: Slope-derived and scree deposits (Late Pleistocene); TRS: terra rossa (colluvium of paleosols sediments) (Late Pleistocene); FGS: Gravel-bed braided fluvial and alluvial fan deposits (Fosso di Genzano Synthem) (Middle Pleistocene); CMA: L’Aquila calcareous breccia, (a) whitish calcareous clayey silts levels (upper Middle Pleistocene); MDS: pelite and sand of meandering fluvial environment (Madonna della Strada Synthem) (Calabrian). SYN: terrigenous foredeep turbidites (Messinian); CRP: ramp-open platform limestone (Miocene); SLB: slope to basin limestone (Paleogene-late Cretaceous); TZPFS: Transfer Zone of the Pettino Fault System; Pettino Fault; SSPF: Synthetic Splay of Pettino Fault; BH: borehole.