Summary The Wasatch Front Community Velocity Model (WFCVM) is the most complete and detailed Earth model for the Wasatch Front region in north-central Utah (USA). Until recently, it had not been well evaluated with strong ground motion observations due to a lack of local earthquakes with magnitude M5+. The 18 March 2020 Mw 5.7 Magna, Utah, earthquake generated excellent strong ground motion data at dozens of stations along the Wasatch Front, with peak ground accelerations up to 0.54 g. Here, we use the forward finite-difference code SW4 to simulate waveforms of the 2020 Magna mainshock in the WFCVM up to 3 Hz and compare its predictions to observations from 35 nearby stations at epicentral distances of 4–46 km. We use a finite fault source model with a semi-stochastic slip distribution and overlay stochastic velocity perturbations (S) and surface topography (T) on the WFCVM, which we refer to as the 3D+S+T model. Observed-predicted amplitude ratios and Goodness-of-Fit (GOF) scores for PGA, PGV, PGD, Arias intensity and duration, cumulative energy and duration are calculated. Our 3D+S+T model performed fairly, matching the general character of the observations with an average GOF score of 5.20 (out of a maximum of 10), slightly better than the unaltered WFCVM score (GOF=4.97). Stochastic velocity perturbations mostly affect peak ground motions at the closest sites ( 20 km), while surface topography improves durations for basin sites and generates more realistic signals at higher frequencies. Neither addition resolves underprediction of basin amplification in the eastern Salt Lake Basin and overprediction of ground motion at basin-edge sites, which likely reflect inaccurate representations of basin structure in the WFCVM. Based on these results, we recommend including stochastic velocity perturbations and topography in future simulations but conclude that updating deterministic models of basin structure will lead to the biggest improvement in forecasting ground motion for future large (M6.75+) earthquakes in the Wasatch Front region.
Hutchings et al. (Thu,) studied this question.