The L'Aquila 2009 event: the GPS deformations

In the night of April 6, 2009, an earthquake of MW 6.3 magnitude occurred in the Abruzzo region. The hypocenter was estimated by the INGV at 42,35� N, 13,38� E, at a 9.5 km depth; moreover, at least one month of pre-seismic events preceded the main shock and aftershocks continued for at least 6 months. For the understanding of the geodetic and geodynamic implications of the earthquake, the temporal and spatial analyses of the phenomenon are fundamental; our research group has collected the GNSS data provided by about 50 permanent stations in the earthquake area and neighbouring regions; all the data have been processed in order to investigate the stations displacements and, if possible, the deformation pattern. In particular, the time series (two months of data both before and after the earthquake) of the daily coordinates were interpolated for each station in order to estimate the displacement at the main shock epoch: particular attention has been paid to carry out a proper covariance empirical estimation, in order to evaluate the displacement significance. Finally, the displacements of all the stations have been spatially analyzed to indentify the areas with similar displacements and the main discontinuities between them. Thirteen stations that significantly displace horizontally have been found: a rough clustering allows us to discriminate between a near field area that displaces mainly southwards, a south-western region that displaces in a SWdirection and a northeast region with an opposite motion. Only four station in the epicenter area significantly displace vertically, with drops between 3 and 12 cm.