Earthquake Focal Mechanism Forecasts and Applications in the PSHA in Italy

Abstract:

The reduction of uncertainties is a primary goal in Probabilistic Seismic Hazard Analysis (PSHA). One of the main sources of uncertainty is associated with the use of the Ground Motion Prediction Equations (GMPEs). Part of the GMPE uncertainties can be reduced improving the forecasts of the focal mechanisms and style of faulting related to the future earthquakes; in other words, it is expected that GMPEs forecasting performances are more accurate and precise if the style of faulting of the next earthquakes is known. In this study, we propose and apply to the Italian territory a procedure to compute, for each spatial cell, the probability to observe in the future a Normal, Reverse, and Strike-Slip event, and the average distribution of the P, T and N axes for each of these types of earthquake. For this purpose we use a significant focal mechanism catalog and the latest present-day stress field data release for Italy. The method is a modification of the Cumulative Moment Tensor introduced by Kostrov (1974), where all data are weighted according to their spatial distance from the cell. This method is applied to the Italian territory that is characterized by a complex tectonic setting because of the N-S convergence of Africa and Eurasian plates and of NE-SW extension, perpendicular to the Apenninic belt, coexistence. The final goal is to provide information that might be helpful for the ongoing activities related to the preparation of the next seismic hazard model for Italy.