Influence of site response and focal mechanism on the performance of peak ground motion prediction equations for the Greek region

The predictive performance of ground motion prediction equations relative to peak horizontal acceleration (PHA) defined for the Greek region were found not to benefit from the inclusion of terms accounting for site response. This can be in part due to an inadequacy of standard methods for site classification to evaluate the expected amount of PHA amplification. Indeed, the adoption of a new method to derive classification from the analysis of regression residuals seems able to improve the predictive performance in comparison to the use of conventional classification. However, this improvement is limited by an intrinsic drawback of classification criteria, i.e. the implicit assumption that amplification be a site-specific property not depending on event characteristics. Instead, for the study area and at least within the range of earthquake magnitude and distance investigated, the inclusion of focal mechanism among the explanatory variables of equations both for PHA and for peak horizontal velocity (PHV) does not improve the predictive performances independently on how fault styles are categorized.