From Ergodic to Region- and Site-Specific Probabilistic Seismic Hazard Assessment: Method Development and Application at European and Middle Eastern Sites

Abstract

The increasing numbers of recordings at individual sites allows quantification of empirical linear site-response adjustment factors (δS2S _s ) from the ground motion prediction equation (GMPE) residuals. The δS2S _s are then used to linearly scale the ergodic GMPE predictions to obtain site-specific ground motion predictions in a partially non-ergodic Probabilistic Seismic Hazard Assessment (PSHA). To address key statistical and conceptual issues in the current practice, we introduce a novel empirical region- and site-specific PSHA methodology wherein, (1) site-to-site variability (φ_S2S) is first estimated as a random-variance in a mixed-effects GMPE regression, (2) δS2S _s at new sites with strong motion are estimated using the a priori φ_S2S, and (3) the GMPE site-specific single-site aleatory variability σ _ss,s is replaced with a generic site-corrected aleatory variability σ₀. Comparison of region- and site-specific hazard curves from our method against the traditional ergodic estimates at 225 sites in Europe and Middle East shows an approximate 50% difference in predicted ground motions over a range of hazard levels—a strong motivation to increase seismological monitoring of critical facilities and enrich regional ground motion data sets.