## 1. Introduction

[2] On April 6th 2009, at 3:32 local time (1:32 UTC), a M_{w} = 6.3 earthquake occurred in the Abruzzi region (central Italy), followed by five M > 5 aftershocks, the largest ones occurring on April 7th (M_{w} = 5.5) and 9th (M_{w} = 5.4) (Figure 1a). The mainshock, located at about 9 km depth, produced severe damage in the ancient city of L'Aquila and in many neighboring villages. Moment tensor solutions reveal normal faulting mechanism consistent with the NE-SW extensional trend of the central Apennines [e.g., *Amato et al.*, 1998]. According to recent geodetic studies, surface geological observations and aftershocks relocations [*Atzori et al.*, 2009; *EMERGEO Working Group*, 2010; *Chiarabba et al.*, 2009], the main fault is identified as the NW striking and SW dipping Paganica Fault.

[3] Inversions of geodetic data for seismic source purposes are often performed implementing the analytical model of *Okada* [1992] of a fault embedded in an elastic, homogeneous and isotropic half-space. It is reasonable to ask: how can material complexities affect slip distribution providing different surface displacement patterns? Analytical and semi-analytical codes such as *Wang et al.* [2003] provide a partial answer to this question, since they allow describing the lithosphere with a 1D vertical layering. However, local asperities, anisotropy and the presence of topography are likely to be present in faulted zones. The above mentioned complexities can be managed only by means of numerical tools. *Masterlark* [2003] tested the sensitivity of finite element (FE) computed slip distributions to common assumptions (e.g., homogeneous, isotropic, Poisson-solid and half-space medium), finding that differences in displacement predictions exceeded the uncertainty bounds. *Hearn and Bürgmann* [2005] investigated the effect of depth-dependent elasticity on slip inversions using FE solutions of a shear dislocation in layered and uniform elastic Earth models. They found that incorporating realistic increases of shear modulus with depth in the inversions modifies the recovered centroid depth and seismic potency with respect to uniform elastic half-space models. *Dubois et al.* [2008] analyzed the influence of structural and rheological heterogeneities on the earthquake deformation cycle, showing significant differences in slip distribution (beyond the associated uncertainty bounds) when using models with fault damage zones and elastic layering.

[4] In this paper, taking advantage of the FE method, we optimize the coseismic displacement data due to the L'Aquila earthquake to retrieve fault slip distributions. We also perform a resolution study to quantify the information we can extract from large coverage interferometric data.