Rapporto preliminare sull'attività in emergenza per l'installazione della rete GPS mobile e la stima delle deformazioni cosismiche alle stazioni CGPS

<p>In this study we use GPS measurements and field observations to infer the fault geometry and the amount of coseismic slip of the causative fault of the 24th August Mw 6.2 Amatrice earthquake. GPS data were analysed by the INGV National Earthquake Center (CNT) using the GIPSY-OASIS, GAMIT-GLOBK and BERNESE software. The final coseismic displacement filed was thus obtained from the combination of the three individual solutions by solving for the combined offstes (unknowns) in a least squares sense<em>. </em>The combined horizontal coseismic displacements for the 24th August mainshock show that the observed offsets are qualitatively consistent with a normal fault striking ~NW-SE and dipping to the SW. The largest displacements were measured at Amatrice (AMAT), which moved to the NW by ~2.5 cm and subsided by ~1.5 cm. Norcia (NRCI) and Leonessa (LNSS) moved SW-wards by ~2.4 and 2.3 cm, respectively, whereas Ascoli (ASCC), which was located on the footwall of the causative fault, moved northeastwards by ~1.4 cm. The other stations moved horizontally by <1 cm in a radius of ~50 km from the epicentre.</p> <p>Preliminary modeling reveals that the causative fault strikes ~NW-SE and dips ~45° to the SW, with an average slip of ~0.6 m (rake -80°), which (using a value of 30 GPa for rigidity) gives an estimated seismic moment of of 2.2  X 10¹⁸ Nm. The variable slip model shows two main asperities with ~1 m of maximum slip, mostly contained within the uniform slip fault. The largest asperity lies at a depth of 1-7 km downdip of the observed surface ruptures sees at the base of the uppermost branch of the Mt. Vettore fault. The second asperity, located SE-wards of the hypocentre, show a more compact slip distribution confined between 3-6 km depth.</p