ShakeMap® implementation in Italy

Italy is a seismically active country which has been site of several large and extremely damaging earthquakes causing hundreds to tens of thousands of casualties since historical times. In recent years, the "Dipartimento per la Protezione Civile" (DPC; Italian Civil Protection - an office dependent directly from the prime minister) has supported the project S4 driven specifically toward fast assessment of ground motion shaking in Italy in order to organize the emergency and direct the rescue teams. The Istituto Nazionale di Geofisica e Vulcanologia (INGV) has implemented the software package USGS-ShakeMap® to obtain maps of the peak ground motion parameters (PGM), and of the instrumentally derived intensities. The calculation of shakemaps at INGV relies mainly on broadband and strong motion data acquired by the Italian seismic network. Shakemap PGM data feeding relies on two concurrent seismic acquisition systems and maps are be determined as quickly as 5 minutes from origin time automatically or within 30 minutes using manually revised locations for earthquakes occurring on the national territory. In Italy, attenuation has been found to vary between different regions. For the smaller events (up to M 5.5) we have implemented a six-areas regionalized model (three separate sets of equations) following the relations of Malagnini and co-workers (Malagnini, et al., 2000; Malagnini, et al., 2002; Morasca, et al., 2006), the same used by the National Seismic Hazard Working Group (2004) for the compilation of the national hazard map; for larger earthquakes, the strong-motion-based equations by Ambraseys et al. (1996) are used. For the site corrections, we have implemented a classification based on the 1:100,000 geology map of Italy compiled and published by the "Servizio Geologico Nazionale". In this case, the geologic units have been gathered into five different classes A, B, C, D and E according to the EuroCode8 provisions, EC8, after Draft 6 of January 2003 on the base of the ground acceleration response. This site classification is compared to that that can be obtained from the analysis of the topographic relief (Allen and Wald, 2007). Examples of shakemaps for both recent M4 size earthquakes and for large, instrumentally recorded 20th century earthquakes that have occurred in Italy will be shown.