Ground motion modeling for the 6 April 2009 earthquake (Mw 6.3) at Poggio Picenze (central Italy)

The town of Poggio Picenze (central Italy), located ~12 km SE of L’Aquila, reported a damage intensity of VIII–IX (MCS) for the 6 April 2009 (MW=6.3) earthquake. In the following days, two stations (M128 and PGG) were operating in the historical centre and recorded several aftershocks. The aim of this paper is to model ground motion at Poggio Picenze for the 6 April 2009 earthquake. First, recordings of 16 aftershocks (2.0≤ML≤4.2), located in the epicentral area of the strong event, are processed to define average shear wave velocity (VS) profiles with depth through the non-linear inversion of Rayleigh wave group velocity dispersion curves of the fundamental mode extracted with the frequency–time analysis. Then, the local average VS model and the regional model, in addition to two shallow downholemeasurements, are used to define two 2-D cross-sections passing through the seismic stations. Ground motion is modeled along such cross-sections for the strongest aftershock (ML=4.2)with the hybrid method consisting of modal summation and finite difference algorithms. Once the modeling results at the M128 and PGG stations are validated, the ground motion is computed for the main shock. Spectral amplifications up to factors 5–6 are estimated at 3–4 Hz for the vertical component and up to factors 2–3 at 2–6 Hz for the radial and transverse components. Ground accelerations are maximum in the horizontal plane, along the transverse component (around 0.4 g) and are half along the vertical component.