HR: 0830h
AN: S11D-0319    [PDF]
TI: Las Vegas Valley Seismic Response Project: Quantification of Basin Response Using 2-D Finite-Difference Ground Motion Simulations
AU: * Pancha, A
EM: pancha@seismo.unr.edu
AF: Nevada Seismological Laboratory and Department of Geological Sciences, Mail Stop 174, University of Nevada, Reno, NV 89557 United States
AU: Louie, J N
EM: louie@seismo.unr.edu
AF: Nevada Seismological Laboratory and Department of Geological Sciences, Mail Stop 174, University of Nevada, Reno, NV 89557 United States
AU: Anderson, J G
EM: jga@seismo.unr.edu
AF: Nevada Seismological Laboratory and Department of Geological Sciences, Mail Stop 174, University of Nevada, Reno, NV 89557 United States
AB: To improve the ability to predict basin effects, we conducted sensitivity tests using 2-D synthetics to evaluate and quantify the effects of basin properties on ground motion. The initial focus of this work is to aid characterization of the seismic response of Las Vegas Valley (LVV), Nevada to underground nuclear explosions at the Nevada Test Site (NTS). This modeling is part of a larger collaborative effort to characterize the basin and its response to ground shaking. Las Vegas Valley is an asymmetric alluvial basin 50 km wide and up to 5 km deep. We generated suites of 2-D elastic finite-difference simulations of seismic wave propagation for a geometry depicting explosive sources at NTS recorded across LVV. Near surface velocity information, derived from refraction microtremor data collected across LVV (Rasmussen et al., 2003, Fall AGU presentation), constrain velocity gradients within the basin and help us investigate effects of geotechnical layers on low-frequency ground motion. Simulation parameters are varied to determine the sensitivity of basin geometry, seismic velocity, basin velocity gradients, and Pg depth on the duration, amplitude, acceleration response spectra, and spectral amplitude of seismic shaking. The observed basin responses are complex, motivating the construction of a least-squares model to recognize average effects of the velocity-model and basin-geometry parameters on various ground motion measures. The least-squares inversion identifies parameters that significantly reduce the misfit responses. A number of linear forms of the model are considered. We can add additional variables to the model so long as error reductions are significant. Initial results indicate that local basin depth, distance from the basin edge, and velocity contrasts are most significant. Influence of Pg depth suggests that the mix of wave types propagating into the basin is an important factor for ground motion. Additional work will include earthquake sources of varying depth and focal mechanism to derive general basin response characteristics to earthquake motion.
DE: 7212 Earthquake ground motions and engineering
DE: 7230 Seismicity and seismotectonics
SC: Seismology [S]
MN: 2003 Fall Meeting