HR: 0830h
AN: S11D-0333    [PDF]
TI: Geophysical Studies of Seismic Hazard in the Tahoe City Sub-basin, Lake Tahoe, California
AU: * Muehlberg, J M
EM: muehlber@unr.nevada.edu
AF: Department of Geological Sciences, Mackay School of Mines, Univ. of Nevada 172, Reno, NV 89557 United States
AU: Schweickert, R A
EM: richschw@unr.edu
AF: Department of Geological Sciences, Mackay School of Mines, Univ. of Nevada 172, Reno, NV 89557 United States
AU: McHugh, J
EM: jmchugh@unr.nevada.edu
AF: Department of Geological Sciences, Mackay School of Mines, Univ. of Nevada 172, Reno, NV 89557 United States
AU: Rasmussen, T
EM: tiana@seismo.unr.edu
AF: Department of Geological Sciences, Mackay School of Mines, Univ. of Nevada 172, Reno, NV 89557 United States
AU: Louie, J N
EM: louie@seismo.unr.edu
AF: Department of Geological Sciences, Mackay School of Mines, Univ. of Nevada 172, Reno, NV 89557 United States
AB: The Lake Tahoe basin has the potential for serious earthquakes and earthquake-related tsunamis. The history of lake level fluctuations should be recorded in sediments beneath the Lake's outlet at Tahoe City. Borehole data show the sediments consist primarily of a thick sequence of lacustrine silts and clays with interbedded sands. Beneath this unit is an older Q-T (?) sand and gravel sequence of unknown origin. The lacustrine deposits locally rest upon 2.0 Ma latites, which in turn rest upon the older sand and gravel sequence. Near the outlet, several fault scarps displace units less than 2.0 m.y. old. These scarps may influence the stability of the dam across the outlet and the sequence and extent of lake level high stands. Our project is integrating geophysical and stratigraphic data to further define and describe the Tahoe City sub-basin. We collected new gravity data to provide an estimate of basin depths across the outlet and help define subsurface faults. Preliminary data suggest the maximum basin depth is 180 m, near the outlet. Refraction microtremor surveys yielded information about stratigraphy and shear velocities of the Quaternary deposits. The average shear wave velocity to 30-m depth obtained for this area is 334 m/s. These values correspond to a NEHRP soil hazard class of D, similar to that found in other lacustrine basins of the region. Soils in this NEHRP class tend to show a significant amplification of shaking, posing increased hazard to structures. We are combining stratigraphic with gravity and seismic data to produce geologic cross sections having information on basin depths and Quaternary faults.
DE: 1219 Local gravity anomalies and crustal structure
DE: 1857 Reservoirs (surface)
DE: 7212 Earthquake ground motions and engineering
DE: 7223 Seismic hazard assessment and prediction
DE: 8010 Fractures and faults
SC: Seismology [S]
MN: 2003 Fall Meeting