GNGTS 2017 - 36° Convegno Nazionale

130 GNGTS 2017 S essione 1.2 Coseismic investigation through the integration of DInSAR measurements and geological and seismological data in a Finite Element environment R. Castaldo Istituto per il Rilevamento Elettromagnetico dell’Ambiente, Consiglio Nazione delle Ricerche (IREA-CNR), Napoli, Italy Introduction. In the last decades, DInSAR measurements have been increasingly exploited to infer the coseismic deformation patterns due to their wide spatial coverage and high accuracy (Massonet et al. , 1993). The inversion of the DInSAR measurements represents a powerful approach for better understanding the fault-zone mechanisms and, consequently, for improving the seismic risk mitigation strategies. Originally, the inversion procedures have been developed by considering an analytical model, often referred to as Okada model (Okada, 1985), based on the hypothesis of an homogeneous-isotropic and elastic half-space and on the assumption of simple planar faults (Pritchard et al. , 2002). More recently, in order to take into account the complexity of the investigated faults involved in the coseismic phase, an effective solution is provided by the joint exploitation of DInSAR measurements and of geological and seismological information within a numerical framework, such as the Finite Element (FE) method (Fagan, 1992). This approach make possible to consider the available information relevant to both the coseismic fault segments and the surrounding faults system, allowing to evaluate the stress and strain field changes (Perniola et al. , 2004): these values represent key elements for characterizing the seismogenic rupture mechanism and for the estimation of its effects on the surrounding region. Hence, the generation of a coseismic model has to benefit of a large amount of geological and seismological data including the information on the medium scale crustal heterogeneities derived from the regional seismic tomography. In order to carry out the modeling procedure, we generally follow five main steps: 1. generation of a fault model based on the interconnected active faults system, extended over a large area containing the involved seismic sequence, as well as on the neighboring active structures; 2. implementation of a model setup, in a FE mechanical environment by exploiting the elastic dislocation theory and integrating the information on the curved geometries of the 3D fault model and those available, through seismic tomography, on the crust heterogeneities; 3. optimization of the model unknowns represented by the rupture patches extent and by the forces applied to the hanging wall and footwall unlocked crustal blocks; 4. ���������� �� ��� ������ ��� ������ ����� ������� ���������� �� ��� ����������� evaluation of the stress and strain field changes associated to the earthquake; 5. ���������� ������� ��� �������� ������������ ��� ������ ��� ������ ��������� ���� comparison between the modelled displacement and stress and strain principal axes and those retrieved from geodetic measurements and the independent geological, seismological data. The proposed procedure is applied on three different main shocks episodes taken place in Italy in last decade: the events occurred on 20 May (Ml 5.9) and 29 May (Ml 5.8), 2012 in Emilia region (Tizzani et al. , 2013), the L’Aquila earthquake occurred on April 6, 2009 (Mw 6.3) and the Amatrice main shock on 24 August 2016 (Ml 6.0) (Lavecchia et al. , 2016). Emilia 2012 earthquake. We provide new insights into the two main seismic events that occurred on 2012 in the Emilia region, Italy. We extend the results from previous studies based on analytical inversion modeling of GPS and RADARSAT-1 DInSAR measurements by exploiting RADARSAT-2 data. Moreover, we benefit from the available large amount of geological and geophysical information through FE method modeling implemented in a structural-mechanical context to investigate the impact of known buried structures on the modulation of the ground deformation field (Fig. 1). We find that the displacement pattern associated with the 20 May event is consistent with the activation of a single fault segment of the inner Ferrara thrust, in good agreement with the analytical solution. In contrast, the