Fast Determination of Moment Tensors and Rupture History: What Has Been Learned from the 6 April 2009 L'Aquila Earthquake Sequence

Abstract

On 6 April 2009, a magnitude Mw = 6.1 earthquake struck the Abruzzi region in central Italy. Despite its moderate size, the earthquake caused more than 300 fatalities and partially destroyed the city of L'Aquila and many surrounding villages. The mainshock was preceded by an earthquake swarm that started at the end of 2008. The largest earthquakes of the swarm included an Mw = 4.0, which occurred on 2009/03/30 at 13:38:26 (UTC), and Mw = 3.9 and Mw = 3.5 events that occurred on 2009/04/05 at 20:48 and 22:39 (UTC), respectively. By the end of November 2009, more than 16,000 aftershocks with ML ≥ 0.5 had been recorded by the INGV seismic network (Figure 1). Current advances in data transmission and communication yield high-quality broadband velocity and strong-motion waveforms in near real time. These data are all crucial for rapid determination of earthquake source parameters ( e.g. , fault geometry, focal depth, and seismic moment). For the L'Aquila mainshock, the velocimeter data of the Italian National Seismic Network (INSN, code IV), MedNet (code MN, station PDG), the North-East Italy Broadband Network (code NI, stations ACOM and PALA), and the SudTirol Province (code SI, station KOSI) were available in real time. In the following days, the strong-motion data of the RAN network (Rete Accelerometrica Nazionale) and, in addition, the displacement data recorded by the Istituto Nazionale di Geofisica e Vulcanologia (INGV) GPS network (Anzidei et al. 2009) also become available. In this study we present a retrospective analysis of the rapid source parameters determination procedure developed at INGV (Scognamiglio et al. 2009) as applied to the L'Aquila seismic sequence. Our approach consists of two stages: the near real-time determination of the seismic moment tensor, which is already routinely performed for all ML ≥ 3.5 earthquakes …