Comparison between empirical predictive equations calibrated at global and national scale and Italian strong-motion data

In the last few years in Italy many ground motion prediction equations (hereinafter GMPEs) were calibrated both at national and regional scale using weak and strong motion data recorded in the last 30 years by several networks. Moreover, many of the strongest Italian earthquakes were included in global data sets in order to calibrate GMPEs suitable for the prediction of ground-motion at very large scale. In the last decade, the Sabetta and Pugliese (1996) relationships represented a reference point for ground motion predictions in Italy. At present all Italian strong-motion data, recorded from 1972 by Italian Accelerometric Network, and more recently by other regional networks (e.g., RAIS, Strong motion network of northern Italy), are collected in ITACA (ITalian ACcelerometric Archive). Considering Italian strong-motion data with Mw≥4.0 and distance (Joyner-Boore or epicentral) up to 100 km, new GMPEs were developed by Bindi et al. (2010), aimed at replacing the older Italian relationships. The occurrence of the recent December 23, 2008, Mw 5.4, Parma (northern Italy) earthquake and the April 6, 2009, Mw 6.3, L’Aquila earthquake, allowed us to upgrade the ITACA data set and gave us the possibility of validating the predictive capability of many GMPEs, developed using Italian, European and global data sets. The results are presented in terms of quality of performance (fit between recorded and predicted values) using the maximum likelihood approach as explained in Spudich et al. (1999). Considering the strong-motion data recorded during the L’Aquila sequence, the considered GMPEs on average, overestimate the observed data, showing a dependence of the residuals with distance in particular at higher frequencies. An improvement of fit is obtained comparing all Italian strong-motion data included in ITACA with the European GMPEs calibrated by Akkar and Bommer (2007a, 2007b) and the global models calibrated by Cauzzi and Faccioli (2008). In contrast, the Italian data seem to attenuate faster than the NGA models calibrated by Boore and Atkinson (2008), in particular at higher frequencies.