An Alternative Analysis of the Probabilistic Seismic Hazard for Las Vegas Valley, Nevada

Probabilistic seismic-hazard calculations relevant for rock-site conditions in the Las Vegas Valley (LVV), Nevada, have been computed. These account for seismic sources not included in the current (2008) U.S. Geological Survey national seismic-hazard model (NSHM) due to insufficient knowledge or documentation, using the commercial software package EZ-FRISK. The LVV is underlain by a system of mapped, active normal faults that comprise the LVV fault system (LVVFS), with maximum potential earthquakes of M 6.8. The 2008 NSHM explicitly includes only one fault of the LVVFS. This analysis includes four more faults of the LVVFS plus four regional faults, in addition to those included in the 2008 NSHM, and modifies parameters of two others. As such, this study demonstrates the effect of a significant modification to expectations for seismic sources. These results can be considered as a "what if" scenario for seismic hazard of the LVV. Nominal peak ground acceleration (PGA) and 5% damped spectral acceleration (SA) were calculated for 0.2 s and 1.0 s periods using five ground-motion prediction equations (GMPEs). A logic-tree formulation accounted for uncertainty in the GMPEs and source parameters. Hazard values for PGA and SA, computed at similar to 2.8 km spacing, are comparable with those of the 2008 NSHM on the margins of the LVV but are considerably higher in the north-central parts of the LVV near downtown Las Vegas and the city of North Las Vegas. The study provides a rationale for the urgency to intensify investigations of faults in and around the LVV.