Strong-Ground-Motion Simulation of the 6 April 2009 L'Aquila, Italy, Earthquake

Abstract

On 6 April 2009, an earthquake of Mw 6:13 (Herrmann et al., 2011) occurred in central Italy, close to the town of L'Aquila. Although the earthquake is considered to be a moderate-size event, it caused extensive damage to the surround- ing area. The earthquake is identified with significant directivity effects: high- amplitude, short-duration motions are observed at the stations that are oriented along the rupture direction, whereas low-amplitude, long-duration motions are observed at the stations oriented in the direction opposite to the rupture. The complex nature of the earthquake combined with its damage potential brings the need for studies that assess the seismological characteristics of the 2009 L'Aquila mainshock. In this study, we present the strong-ground-motion simulation of this particular earthquake using a stochastic finite-fault model with a dynamic corner frequency ap- proach. For modeling the resulting ground motions, we choose two finite-fault source models that take into account the source complexity of the L'Aquila mainshock. In order to test the sensitivity of ground-motion parameters to the seismic wave attenua- tion parameters, we use two different attenuation models obtained in the study region using weak-motion and strong-motion databases. Comparisons are made between the attenuation of synthetics and ground-motion prediction equations (GMPEs). Synthetic ground motions are further compared with the observed ones in terms of Fourier amplitude and response spectra at 21 strong-ground-motion stations that recorded the mainshock within an epicentral distance of 100 km. The spatial distribution of shaking intensity obtained from the Did You Feel It? project and site survey results are compared with the spatial distributions of simulated peak ground-motion intensity parameters. Our results show that despite the limitations of the method in simulating the directivity effects, the stochastic finite-fault model seems an effective and fast tool to simulate the high-frequency portion of ground motions.