Ground-Motion Prediction Equations for Region-Specific Probabilistic Seismic-Hazard Analysis

The goal of this article is to investigate the possibility of reducing the uncertainty of the ground motion predicted for a specific target area (Po Plain and northeastern Italy), by calibrating a set of ad hoc ground-motion prediction equations (GMPEs). The derived GMPEs account for peculiarities that are not generally considered by standard predictive models, such as (1) an attenuation rate dependent on distance ranges and geological domains; (2) enhancement of short-period spectral ordinates, due to the reflection of S waves at the Moho discontinuity; and (3) generation of surface waves inside an alluvial basin. The analyzed strong-motion dataset was compiled by selecting events in the 4.0-6.4 magnitude range, records with distances shorter than 200 km, and focal depths shallower than 30 km; the major contribution comes from the recent 2012 Emilia sequence (first mainshock, 20 May 2012 M-w 6.1; second mainshock, 29 May 2015 M-w 6.0). The GMPEs are derived for the geometrical mean of horizontal components of peak ground acceleration, peak ground velocity, and 5% damped spectral acceleration in the 0.04-4 s period range. The derived region-specific models led to a reduction of the hazard levels for several intensity measures, with respect to the values obtained by considering the reference Italian attenuation model (Bindi et al., 2011), as exemplified by the comparison of the hazard curves computed for two specific sites. Online Material: Database of Northern Italy (DBNI) flat-file and tables of northern Italy ground-motion prediction equations (GMPEs) (NI15) regression coefficients and variability components for use with Joyner-Boore and hypocentral distances.