HR: 0830h
AN: S11D-0320    [PDF]
TI: Shallow Shear Velocity and Seismic Microzonation of the Las Vegas Urban Basin
AU: * Rasmussen, T
EM: tiana@seismo.unr.edu
AF: Dept. of Geological Sciences, Mackay School of Mines, Univ. of Nevada 172, Reno, NV 89557 United States
AU: Smith, S B
EM: sbsmith@unr.edu
AF: Dept. of Geological Sciences, Mackay School of Mines, Univ. of Nevada 172, Reno, NV 89557 United States
AU: Clark, M
EM: mclark@seismo.unr.edu
AF: Nevada Seismological Lab, Mackay School of Mines, Univ. of Nevada 174, Reno, NV 89557 United States
AU: Lopez, C
EM: ctlopez@unr.edu
AF: Dept. of Geological Sciences, Mackay School of Mines, Univ. of Nevada 172, Reno, NV 89557 United States
AU: Loughner, C
EM: loughner@seismo.unr.edu
AF: Nevada Seismological Lab, Mackay School of Mines, Univ. of Nevada 174, Reno, NV 89557 United States
AU: Park, H
EM: hpark@unr.edu
AF: Dept. of Geological Sciences, Mackay School of Mines, Univ. of Nevada 172, Reno, NV 89557 United States
AU: Scott, J B
EM: jscott@seismo.unr.edu
AF: Nevada Seismological Lab, Mackay School of Mines, Univ. of Nevada 174, Reno, NV 89557 United States
AU: Thelen, W
EM: wethelen@seismo.unr.edu
AF: Nevada Seismological Lab, Mackay School of Mines, Univ. of Nevada 174, Reno, NV 89557 United States
AU: Greschke, B
EM: passcal@passcal.nmt.edu
AF: IRIS-PASSCAL Instrument Center, New Mexico Tech, 100 East Road, Socorro, NM 87801 United States
AU: Louie, J N
EM: louie@seismo.unr.edu
AF: Nevada Seismological Lab, Mackay School of Mines, Univ. of Nevada 174, Reno, NV 89557 United States
AB: In July 2003 we performed a seismic microzonation study of the Las Vegas basin along a 15 kilometer transect. Using 120 Reftek RT-125 "Texans" on loan from PASSCAL, we completed this transect in two days. 4.5-Hz geophones collected Rayleigh-wave data for dispersion analysis and velocity-profile modeling. Only passive urban seismic noise sources are needed for this refraction microtremor analysis; freeway and commuter traffic are used in this case. Using a geophone spacing of 20 meters, fifty 260-m array sections were analyzed to create a transect of 30-m shear velocity measurements 15 km long. The transect runs approximately parallel to Interstate 15 from Cheyenne Avenue at the north to Tropicana Avenue at the south, passing most of The Strip and downtown Las Vegas. We added a few refraction lines, with a sledgehammer source, to augment the microtremor dispersion data with P velocities. The lowest shear velocities observed in Las Vegas are in the NEHRP class D range, at 230 m/s, well above the NEHRP class E range. These lower velocities are found near Interstate 15 and Lake Mead Blvd. Velocities then rise smoothly southward to the middle of the NEHRP-C range (450-600 m/s) near Sahara Blvd. to the south. There appears to be a slight decline further south to Tropicana Blvd. Our results from only 3 km out of the 15-km-long transect have velocities near or below the NEHRP-C/D boundary at 350 m/s. This survey suggests a medium-scale study with a limited budget can be completed in a short time. The study is a crucial new step in the characterization of the effects of ground shaking due to a seismic source in the surrounding region. Similar studies have been completed in the Reno area basin and in the Los Angeles Basin. All of these studies suggest that shallow shear velocity does not correlate well with geologic map units. The range of velocities within one map unit is greater than the average difference between units.
UR: http://www.seismo.unr.edu/hazsurv
DE: 0935 Seismic methods (3025)
DE: 5194 Instruments and techniques
DE: 6334 Regional planning
DE: 7212 Earthquake ground motions and engineering
DE: 7223 Seismic hazard assessment and prediction
SC: Seismology [S]
MN: 2003 Fall Meeting