The effect of bounds on magnitude, source-to-site distance and site condition in PSHA-based ground motion selection

Abstract

In this paper, the effect of using bounds on magnitude, source-to-site distance, and site condition of prospective records for the purpose of ground motion selection based on probabilistic seismic hazard analysis (PSHA) is investigated. Although it is common in ground motion selection to consider bounds on these causal parameters, there is no consistent approach for setting the bounds as a function of the seismic hazard at the site, and no guidance exists on how the bounds should be set considering the distribution of causal scenarios affecting PSHA results. 36 PSHA cases are considered in this paper to empirically illustrate the effects of alternative bounds on the characteristics of selected ground motions, which cover a wide range of deaggregation distributions and site conditions. The obtained results indicate that the use of excessively narrow bounds encompassing only the dominant causal scenario can lead to ground motion ensembles with a biased representation for the target hazard. In contrast, the use of relatively wide bounds results in ensembles with an appropriate representation for the target intensity measure distributions. Quantitative criteria for determining such bounds for general problems are provided, which are expected to be sufficient in the majority of problems encountered in ground motion selection for seismic demand analyses.