GNGTS 2017 - 36° Convegno Nazionale

162 GNGTS 2017 S essione 1.2 Within a lapse of about five months (24 August 2016 to 18 January 2017), the CISS released four major neighboring events, with magnitude M w between 5.5 and 6.5, along a WSW-dipping normal fault system extending for a length of about 70 km (Chiaraluce et al. , 2017). The system consists in two en echelon master faults, Vettore Mt. and Gorzano Mt., articulated in segments and sections, and possibly connected at a depth of about 8 km (Lavecchia et al. , 2017). An impressive co-seismic ground rupture with an along-strike extent of 37 km and a maximum vertical offset of 2m was generated along the Vettore fault (Open Emergeo Working Group, 2017). The long-term geology and kinematics of the AQSS and the CISS epicentral areas are well known in the literature, mainly due to the spectacular exposures of both Quaternary active normal faults and pre-existing LateMiocene-Early Pliocene fold-and-thrust structures (Lavecchia,1985; Boncio et al. , 2004).As well, good-quality seismological data are available; they consists of both hypocentral relocation of aftershock sequences registered soon after the main events (Chiaraluce et al. , 2011 and 2016), and of minor sequences and background seismicity. A complete dataset of focal mechanisms is also available, together with a large amount of interferometric and geodetic data. Based on morphotectonic, geological, interferometric and seismological input data, we have reconstructed the non-planar, interconnected pattern of first-order and subsidiary faults, directly and indirectly associated with the AQSS and CISS (Figs. 2 and 3). The 3D reconstruction was performed by adopting the multi-step workflow, outlined in Lavecchia et al. (2017): 1 st step) compilation of a unified and detailed fault trace database in GIS, with faults kinematics and hierarchy; 2 nd step) building of «Fault Ribbons» obtained by projecting the surface traces to depths of 2-3 km depth (with the MOVE Midland Valley extrusion tool); 3 rd step) 2D extrapolation to depth of the fault traces by integration of geological and seismological data. Along a large number of closely-spaced and differently oriented cross- sections, the Fault Ribbons are connected with the best-fitting planes across the underlying hypocentral volumes, also taking into account dip-direction and dip-angle of both the outcropping faults and the preferential planes from focal mechanisms; 4 th step) 3D fault model building. The fault surfaces, with variations along strike and dip, are obtained with the Midland Valley Move Software by interpolating and/or extrapolating the previously built map-view and section-view representation of the Quaternary faults and of the corresponding seismogenic patches. Aweight is assigned to the quality of input constraints and to the accuracy of each fault model. Obtained results give the opportunity to afford a number of discussion point: Fig. 2 - 3D fault model of L’Aquila 2009 Seismic Sequence, from Lavecchia et al. (2017) (on the right) and from Castaldo et al. (submitted to JGR) (on the left); the hypocentral data set is from Chiaraluce et al. (2011).

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