PRELIMINARY COMPARISON OF GROUND MOTIONS FROM EARTHQUAKES IN ITALY WITH GROUND MOTION PREDICTION EQUATIONS FOR ACTIVE TECTONIC REGIONS

Empirical ground motion prediction equations utilized in Italy are based on local databases of recordings from Italian and/or European earthquakes, which are generally shallow crustal events. For events of this type, alternative ground motion prediction equations are used elsewhere in the world that are based on a much larger data inventory. The implicit assumption associated with the use of local (Italian/European) relations is that the characteristics of the local ground motions are different from those in other tectonically active regions. We investigate whether such differences exist for the ground motion parameter of average peak horizontal acceleration. Italian data from predominantly normal fault shallow crustal earthquakes (M=5.1-6.9) recorded at distances up to 200 km are used to compare several key attributes of the Italian data to a well-known relation for worldwide active regions. One such attribute is site effects, for which we find a nonlinear rock-to-soil amplification that is similar to the worldwide model. This nonlinear site response is a significant finding of this study that had not been observed previously with European data. The other two attributes investigated are magnitude and distance scaling, for which some differences were observed from the worldwide model. However, the significance of those differences cannot yet be properly assessed due to apparent correlations between the magnitude- and distance-scaling parameters that are not yet fully understood.