Seismic wave propagation and basin amplification in the Wasatch Front, Utah

Seismological Research Letters
By: , and 

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Abstract

Ground‐motion analysis of more than 3000 records from 59 earthquakes, including records from the March 2020 MwMw 5.7 Magna earthquake sequence, was carried out to investigate site response and basin amplification in the Wasatch Front, Utah. We compare ground motions with the Bayless and Abrahamson (2019; hereafter, BA18) ground‐motion 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  sT<0.5  s) and a correlation between period and the distance over which the discrepancy manifests (2050  km∼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 (T1  sT≳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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Publication type Article
Publication Subtype Journal Article
Title Seismic wave propagation and basin amplification in the Wasatch Front, Utah
Series title Seismological Research Letters
DOI 10.1785/0220200449
Edition Online First
Year Published 2021
Language English
Publisher Seismological Society of America
Contributing office(s) Earthquake Science Center, Geologic Hazards Science Center
Country United States
State Utah
Other Geospatial Wasatch Front
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