Postseismic Viscoelastic Relaxation Following the L'Aquila 2009 Earthquake: Implications for Lithospheric Rheology of the Apennines

Abstract:

In this work we use GPS data to study the postseismic viscoelastic relaxation related to the MW 6.3 normal faulting earthquake that struck the city of L'Aquila (Central Apennines, Italy) on April 6, 2009. Only a limited number of normal-faulting earthquakes have geodetic measurements of viscoelastic relaxation and there is limited knowledge of the viscosity structure of the lower crust/upper mantle in the Central Appennines. Since this region is currently experiencing active extension that gives rise to normal-faulting seismicity, the estimation of the typical relaxation time of the region is of great interest for interseismic strain-rate estimations and to better understand how extension is accommodated beneath the upper seismogenic crust. GPS data are processed by using GIPSY/OASIS software. Particular care has been taken to estimate and correct for the interseismic deformation and the early afterslip deformation, well documented by GPS and InSAR (D’Agostino et al., 2012). A particularly interesting signal observed in the time series is related to hydrological loading with seasonal and multi-annual periodicities. Here we present the preliminary results of the comparison between about 5 years of postseismic deformation recorded at permanent GPS stations, and the surface deformation expected running different viscoelastic models in order to estimate best-fit rheological parameters. Forward models are generated by means of the PSCMP/PSGRN code (Wang et al. 2006). Preliminary results will be presented and possible implications for the mechanism of active crustal extension in general and of the Apennines in particular, will be discussed.