ALBERT

Description: Seismic source models for probabilistic seismic hazard analysis (PSHA), except when using zoneless approaches based directly on the earthquake catalog, invariably include area-source zones, even if active fault sources are modeled explicitly. Because most modern ground-motion prediction equations (GMPEs) employ source-to-site distance metrics defined relative to extended fault ruptures rather than to the epicenter or hypocenter, it becomes necessary to generate virtual fault ruptures within the area-source zones to enable calculation of the correct distance of each earthquake scenario from the site of interest. For a site-specific PSHA, the work of defining the virtual rupture characteristics such as strike, dip, and style of faulting, for more distant source zones, and the computational effort of simulating these ruptures for each earthquake scenario in the hazard calculations, may be unnecessary. Beyond a certain distance from the site, it can be demonstrated that the loss of accuracy introduced by modeling the individual earthquake scenarios as point sources rather than as extended ruptures is usually sufficiently small to allow the distance metric in the GMPEs to be treated as epicentral or hypocentral distance. Such simplifications can significantly increase the efficiency of the hazard calculations and also relieve the seismic source modelers of considerable effort to characterize virtual ruptures far beyond the host zone of the site. Treating earthquake scenarios in the more remote source zones as points also brings the additional benefit of avoiding problems that can arise with the largest magnitude scenarios leading to ruptures that approach the site in cases for which the ruptures are not constrained to remain within the source boundaries.