Ground-motion analysis of more than 3000 records from 59 earthquakes, including records from the March 2020 M-w 5.7 Magna earthquake sequence, was carried out to investigate site response and basin amplification in theWasatch Front, Utah. We compare ground motions with the Bayless and Abrahamson (2019; hereafter, BA18) groundmotion model (GMM) for Fourier amplitude spectra, which was developed on crustal earthquake records from California and other tectonically active regions. The Wasatch Front records show a significantly different near-source rate of distance attenuation than the BA18 model, which we attribute to differences in (apparent) geometric attenuation. Near-source residuals show a period dependence of this effect, with greater attenuation at shorter periods (T < 0:5 s) and a correlation between period and the distance over which the discrepancy manifests (similar to 20-50 km). We adjusted the recorded ground motions for these regional path effects and solved for station site terms using linear mixed-effects regressions, with groupings for events and stations. We analyzed basin amplification by comparing the site terms with the basin geometry and basin depths from two seismic-velocity models for the region. Sites over the deeper parts of the sedimentary basins are amplified by factors of 3-10, relative to sites with thin sedimentary cover, with greater amplification at longer periods (T greater than or similar to 1 s). Average ground-motion variability increases with period, and long-period variability exhibits a slight increase at the basin edges. These results indicate regional seismic wave propagation effects requiring further study, and potentially a regionalized GMM, as well as highlight basin amplification complexities that may be incorporated into seismic hazard assessments.
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