Las Vegas Seismic Response Project:
Shallow Soil Effects
UNLV Engineering Geophysics Laboratory (EGL) Participants Barbara Luke, Ph.D., P.E., Principal Investigator
Ying Liu, Graduate Research Assistant
Vance Skidmore, Undergraduate Research Assistant
Vu Phan, Undergraduate Research Assistant
  Project Collaborators Project lead: Dave McCallen, Ph.D., Lawrence Livermore National Laboratory
UNLV Collaborator: Catherine Snelson, Ph.D., Department of Geoscience
UNR Collaborators: John Anderson, Ph.D. and John Louie, Ph.D. Department of Geological Sciences
  Overview Ground motion data from earthquakes and underground nuclear tests recorded at different locations around the Las Vegas basin have revealed significant differences in amplitude and spectral content from one site to another. We know that these differences are due at least in part to the geologic structure of the basin. However, we know that shallow soil properties can also have a profound effect on the motion at the ground surface. Our research will answer the following question: To what extent can the geographical differences in response that we have observed historically be attributed to differences in characteristics of the shallow subsurface?
  Project We have identified eight sites with "legacy" seismic ground-motion data from nuclear testing. The research team is gathering information from various government and private entities about the geotechnical and geomechanical characteristics of the sites. The information on soil type, density, and seismic wave propagation velocities will be used to estimate seismic response of the shallow soil column, assuming one-dimensional equivalent-linear vertical propagation of horizontally-polarized seismic energy. The analysis of ground motion will done using both Shake2000 and SAC2000 software packages. We will deconvolve ground motion measured on rock, at the edges of the basin, to create a hypothetical input motion at the model halfspace, and compare calculated ground-surface motions with data measured at the eight sites. Two more sites in the northeast quadrant of the basin have also been selected for study. These lack legacy ground motion data, but are important because they are in the deepest part of the basin and this area has been developed since the days of underground nuclear testing. Results of our research will become a part of a larger study, headed by Lawrence Livermore National Laboratory, in which the seismic response of the Las Vegas basin, and the effects of the ground motion on structures, will be estimated using a large computer-driven model.

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