FEM models of coseismic deformation measured by DInSAR: Wenchuan (China) 2008 and L' Aquila (Italy) 2009 earthquakes

We develop a procedure to perform linear inversions of spatially dense geodetic data (DInSAR displacements maps) of earthquakes. The technique is based on the Finite Element Method (FEM) and accounts for a more realistic description of the earth crust. The method consists in three steps. First the creation of the finite element mesh describing the fault system embedded in the local crust. Second the implementation of the mesh into the FEM solver and the computation of the fault Green functions. Third the combination of FEM generated Green functions with linear inversion methods to retrieve the slip distribution on fault plane. The FEM based method is used to explore two earthquakes with significantly different magnitude: the L’Aquila 2009 earthquake, Italy and the Wenchuan 2008 earthquake, China. The Mw 6.3 L’Aquila earthquake occurred on the 6th April of 2009 is generated by a SW dipping normal fault with 20 km of length and is related with the extensional tectonics of the central Apennines Mountain Range. The Mw 7.9 Wenchuan earthquake, occurred on the 12th May 2008, and characterized by a thrust faulting mechanism with dextral component, took place within the context of the Long Term uplift of the Longmen Shan Range in the Eastern Tibet. The seismic event ruptured approximately 280 km of the Beichuan-Yingxiu fault and about 70 km of the Guanxian-Anxian fault. The dataset available for these earthquakes were different. Indeed the L’Aquila earthquake is imaged by ascending and descending orbits of COSMO SkyMed and ENVISAT satellite missions while for the Wenchuan earthquake only the ALOS-PALSAR ascending orbit is available. The DInSAR data are integrated with 6 near field GPS data for the L’Aquila case and with 158 GPS data for the Wenchuan earthquake. Finally we retrieve slip distribution for both the L’Aquila and Wenchuan earthquakes in a heterogeneous and topographic medium and we perform for each one the comparison with the respective homogeneous and flat model. Results highlight the influence of the medium complexities in both Wenchuan and L’Aquila cases, the homogeneous and heterogeneous models reveals differences in slip distribution values up to 20%. Accounting for the topographic relief in the model produces more appreciable effects for the Wenchuan earthquake, where height variations are more significant with respect to the L’Aquila region.