Exploring Basin Amplification Within The RenoMetropolitan Area Using A Magnitude 6.2 ShakeOutScenario

Abstract:

Paleoseismic studies indicate the Mount Rose fault system has a history of significant Holocene earthquakes presenting significant seismic risks for the ~400,000 residents of the Reno metropolitan area of western Nevada. In order to help explore this risk we leveraged SW4, a physics-based wave-equation modeling tool to develop the Reno ShakeOut Scenario, a 3D simulation for a potential magnitude 6.2 earthquake on the fault. This simulation used a material property model generated by aggregating Vs30 measurements, a regional Digital Elevation Model and gravimetry results into a continuous 3D raster file. Comparing simulations of the Thomas Creek (2015 Mw 4.4) and Mogul (2008 Mw 5.0) events to ground-truth seismic records evaluated the material-property model’s quality. A Mw 6.2 Graves and Pitarka rupture drives wave propagation to create the Reno ShakeOut Scenario exploiting this material property model, to enhance our understanding of regional risk. The results indicated that there is a potential for widespread ground shaking at Modified Mercalli Intensity scale (MMI) magnitudes between VII and VIII (Very Strong to Severe ground shaking), with small areas achieving IX (Violent) motions. Distributions of high shaking are controlled by proximity to the rupture, Vs30 values and most significantly basin thickness. Comparisons between SW4 peak ground velocity (PGV) calculations and PGV estimates computed from the Campbell Bozorgnia (2008) empirical ground-motion model (GMM) indicate that there is significant basin amplification occurring. The 2018 USGS National Seismic Hazard Model (NHSM) currently forecasts a 10% chance of this region experiencing severe ground shaking and 2% for achieving violent shaking within the next 50 years. Since the NHSM assumes no basins within the shakeout domain and firm 760 m/s , soil it is likely that the actual risk is higher. This information helps improve our understanding of regional risk by highlighting the hazard inherent in these basin effects.