A Revised Ground‐Motion Prediction Model for Shallow Crustal Earthquakes in Italy

Abstract

This work aims to revise the Bindi et al. (2011) ground-motion model for shallow crustal earthquakes in Italy (hereinafter, ITA10), calibrated in the magnitude range 4.0–6.9 using strong-motion data recorded up to the 2009 L’Aquila sequence. The improvement of ITA10 is needed because of the large number of strong-motion records made available in Italy after the occurrence of the most recent seismic sequen- ces (2012 Emilia, Northern Italy; 2016–2017 Central Italy). The new data collection allows us to extend the magnitude range beyond 6.9 and to include vibration periods up to 10 s. Instead of the geometric mean of the horizontal components of ground motion, the median of orientation independent amplitudes (RotD50) is selected as a measure of the ground-motion parameters, and the rupture distance is introduced as an alternative source-to-site metric to the Joyner–Boore distance (RJB). The site effects are accounted for by a linear dependence on the time-averaged shear-wave velocity in the upper 30 m, VS30. A breakdown of the ground-motion variability is performed into between-event and site-to-site components to make the model suitable for the evaluation of nonergodic probabilistic seismic hazard. We also build a heteroscedastic model for aleatory variability as a function of moment magnitude and VS30. The evaluation of the epistemic uncertainty in the median prediction is also provided to be introduced in the logic trees for the probabilistic seismic hazard assessment. We obtain changes in median predictions with respect to ITA10 at distances lower than 10 km and for strong events (Mw >6:5);moreover,thetotalstandarddeviationsaresignificantlyloweratintermedi- ate and long periods, with an average reduction of about 20%.