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Comparing Physics-Based Next-Level ShakeZoning Computations with USGS ShakeMap Statistics for Southern Nevada Earthquake Scenarios

William H. Savran, Brady Flinchum, Gabriel Plank, Colton Dudley, Nicholas Prina, & John N. Louie

Accepted 2011, SCEC Contribution #1474

A group of students at the Nevada Seismological Laboratory (NSL) are modeling earthquakes on several southern Nevada faults surrounding Las Vegas Valley using the physics- and geology-based “Next-Level ShakeZoning” process; and alternatively the statistical USGS ShakeMap tool. Next-Level ShakeZoning involves using the ModelAssembler Community Modeling Environment to generate geologic-model grids from geotechnical shear-velocity and basin-thickness maps. The USGS Qfaults database suggests source parameters pertaining to each fault. The earthquake scenarios also use the new Clark County Parcel Map containing 10,721 geotechnical Vs30 shear-velocity measurements, yielding the most realistic models of earthquake ground motion to date. Our seismic wave-propagation modeling covers the 0.1 Hz to 0.5 Hz band, and uses a Gaussian time-history distribution for the low-frequency shaking that would affect the larger structures in the Valley. The E3D wave modeler from Lawrence Livermore National Labs simulates the propagation of the seismic waves through the 3-D ShakeZoning grid, with viscoelastic attenuation but without free-surface topography. The scenarios are visualized through peak ground velocity (PGV) maps and movie simulations of seismic-wave propagation. The ShakeMap statistical approach also provides a PGV map, which allows for comparisons to be made between PGV maps, and comparisons to recorded ground motions. Several scenarios are showing significant differences in patterns of shaking amplification across the valley, when the Next-Level ShakeZoning maps are compared to ShakeMap results. For example, the Frenchman Mountain scenario shows PGV of the two approaches within 15% near the source, but upwards of 200% amplification or de-amplification, depending on location, throughout the Valley.

Savran, W. H., Flinchum, B., Plank, G., Dudley, C., Prina, N., & Louie, J. N. (2011). Comparing Physics-Based Next-Level ShakeZoning Computations with USGS ShakeMap Statistics for Southern Nevada Earthquake Scenarios. Oral Presentation at NWRA Symposium 2011.