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

Abstract

In Italy in the last years 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 Italian strongest earthquakes were included in global datasets in order to calibrate GMPEs suitable to predict ground-motion at very large scale. In the last decade the Sabetta and Pugliese (1996) relationships represented a reference for the ground motion predictions in Italy. At present all Italian strong-motion data, recorded from 1972 by RAN (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. (2009), aimed at replacing the older Italian relationships. The occurrence of the recent 23rd December 2008, Mw 5.4, Parma (Northern Italy) earthquake and the 6th April 2009, Mw 6.3, L’Aquila earthquake, allowed to upgrade the ITACA data set and gave us the possibility to validate 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, in 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 (2007 a,b) and the global models calibrated by Cauzzi and Faccioli (2008). In contrast, Italian data seem to attenuate faster than the NGA models calibrated by Boore and Atkinson (2008), in particular at higher frequencies.