Group , Poster #041, Ground Motions

Low-Frequency Examination of Synthetic Reno-Area Basin Amplification from M3 Earthquakes at a Variety of Azimuths

Lauren M. Lewright, Aditya Prathap, Chelsey E. Assor, Jenna R. Graham, & John N. Louie
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Poster Presentation

2021 SCEC Annual Meeting, Poster #041, SCEC Contribution #11472 VIEW PDF
Seismic waves travel with greater amplitude and slower speeds when moving through soft sedimentary rock, relative to hard bedrock. Seismic hazard in the Reno area is increased due to the city’s location within a thin (<1 km) sedimentary basin, where energy from seismic waves can be trapped and ground motion amplified. In order to study the extent to which ground motion in the basin is amplified compared to the bedrock, we are using the SW4 code from LLNL/geodynamics.org to simulate seismic wave propagation through the Reno area for six different M3 earthquakes, to a maximum frequency of 1.11 Hz. After compiling SW4 for the first time under MacOS Big Sur for Apple’s new M1 chip, we ran SW4... on personal laptops for about 16 hours to complete each scenario. We are using Eckert’s 3D community velocity model for the basin, on which he based the M6.3 Reno ShakeOut Scenario computation to 3.125 Hz. At a grid spacing of 120 m, this velocity model has a minimum shear-wave velocity of 609 m/s, yielding at least 4.57 grid points per minimum wavelength. PGV maps produced from these models will allow us to compare shaking at basin versus bedrock sites, and how it changes based on the location of the earthquake. Preliminary indications are that the standard deviation of basin-over-bedrock ground-motion ratios will be a substantial proportion of the average ratio. These results will help in determining the basin’s amplification effects when assessing seismic hazard in the Reno area, and other urban basins.
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