Linear Inversion of GPS data of the 2009 L'Aquila Earthquake by means of a 3D Finite Element Approach

The L'Aquila earthquake (Mw 6.3) occurred on April 6th at 01:32 UTC in the Central Appennines at a depth of about 9 km and was felt all over the central Italy. The main shock was preceded by a long seismic sequence started several months before and was followed by thousands of aftershocks, some of them with Mw>4. In this work we present a 3D Finite Element (FE) study of the co-seismic deformation field produced by the L'Aquila earthquake and investigated the slip distribution on the fault. Our approach is based on a fully 3D parametrization of the spatial domain by means of a high resolution hexahedral mesh, discretized using 20-nodes brick elements. The element horizontal size is biased from 300 m to 2-3 km using the paving meshing algorithm in combination with an appropriate adaptive sizing function. Real surface topography (500 m) and rheological heterogeneities, deduced from a vp/vs travel time tomographic model, were incorporated within the model. The seismic source has been modeled as a normal fault plane having an heterogeneous moment release. We first computed the co-seismic deformation field by a direct simulation and then the Green's functions, to retrieve the slip distribution on the fault by linear inversion of different GPS datasets. Our results show that the adoption of a realistic 3D domain has a sensible impact on the rupture slip distribution, confirming that a simple halfspace approach introduces some trade-off between domain homogeneity and source complexity.