Topographic Effects in Probabilistic Seismic Hazard Analysis: The Case of Narni, Central Italy

Abstract

This study presents a probabilistic method for estimating the ground motion hazard at sites presenting topographic irregularities. This method is applicable to topographic crests or ridges which may affect site response, producing 2D (or 3D) amplification effects. The method is based on a set of 2D numerical analyses that are carried out using multiple accelerograms from worldwide weak and strong earthquakes recorded on rock. Numerical analyses are performed to compute site-specific frequency-dependent amplification factors to be included into the ground motion prediction equation used in the seismic hazard computation. The hazard at the top of the ridge is then assessed by running a conventional probabilistic seismic hazard analysis (PSHA) with the attenuation relationship modified to include the site response. An application to the case study of Narni (Central Italy) is presented in this work.