Implementation of basin models and sediment depth terms in the 2023 update of the U.S. National Seismic Hazard Model: Example from Reno, Nevada

We present a framework to evaluate the inclusion of candidate basin depth models in the U.S. Geological Survey National Seismic Hazard Model. We compute intensity measures (peak and spectral amplitudes) from uniformly processed earthquake ground motions in and around the basin of interest and compare these to ground-motion model (GMM) estimates over a range of oscillator periods. The GMMs use depth to specific shear-wave velocity isosurfaces (Z_x) as a proxy for basin depth. We quantify whether the GMM estimates using Z_x from the candidate basin depth model outperform the default estimates based on V_S30 (the time-averaged shear wave velocity in the upper 30 m). We partition GMM residuals into event and site terms and compare site terms for stations within the basin to non-basin sites. We apply this framework to the greater Reno, Nevada, region, which has shallow basin depths (less than 450 m) and empirical amplifications of up to a factor of 2.2 at 1.0 s. There are no strong trends in site terms with basin depth, and the use of Z_x values from the new candidate basin model shows marginal improvement of GMM total residuals compared to the default V_S30-based model (the condition of no relative basin amplification).