HR: 0830h
AN: S11D-0321    [PDF]
TI: Crustal Velocity Model of Watusi and Legacy Seismic Refraction Data, Clark County, Nevada
AU: * Zaragoza, S A
EM: szargo@physics.unlv.edu
AF: Department of Geoscience, University of Nevada Las Vegas, 4505 Maryland Parkway MS 4010, Las Vegas, NV 89154-4010 United States
AU: Snelson, C M
EM: csnelson@unlv.edu
AF: Department of Geoscience, University of Nevada Las Vegas, 4505 Maryland Parkway MS 4010, Las Vegas, NV 89154-4010 United States
AU: McEwan, D
EM: mcewand@unlv.edu
AF: Department of Geoscience, University of Nevada Las Vegas, 4505 Maryland Parkway MS 4010, Las Vegas, NV 89154-4010 United States
AU: Sandru, J
EM: sandru@unlv.edu
AF: Department of Geoscience, University of Nevada Las Vegas, 4505 Maryland Parkway MS 4010, Las Vegas, NV 89154-4010 United States
AU: Hirsch, A C
EM: achirsch@csbsju.edu
AF: Department of Geology, St. John's University, Box 745, Collegeville, MN 56321 United States
AB: Clark County, Nevada is located in the southern portion of the Basin and Range Province. As such, it has undergone tremendous extensional forces that produced numerous north-trending ridges and basins. Little is known regarding the crustal structure of the southern Basin and Range. Extension along the Las Vegas Valley Shear Zone (LVVSZ) has produced a northwest-trending corridor of particular interest that may channel seismic energy into the Las Vegas basin. Potential sources include energy produced by earthquakes as well as nuclear testing, should the Nevada Test Site (NTS) become active in the future. Previous studies include a crustal velocity model in the form of a fence diagram by Prodehl (1979) based on Legacy data, seismic refraction experiments performed when the NTS was active. Legacy data were collected on seismometers placed at intervals greater than or equal to 500 m. Seismic sources included chemical blasts and nuclear test shots. To examine whether structures along the corridor would cause seismic energy to dissipate or to transmit into the basin, in September 2002 we utilized 400 seismic instruments to record the Watusi chemical blast at the Nevada Test Site. The profile extended from Ann Road and I-95 northwest to the town of Indian Springs, where the station spacing was 125 m. The blast was located 65 km away from the first station and was expected to have the energy equivalent to 40,000 tons of TNT. However, most of the energy was lost into the air. In addition, falling debris produced diffractions in the data. We picked first arrivals and analyzed these data with forward modeling utilizing MacRay ray-tracing software, integrating these with Prodehl's model to produce an updated, higher resolution crustal velocity model. The model indicates velocities of the upper to lower crust, into the Moho, with average velocities of approximately 6 km/s. Further studies will include integrating data from the Seismic Investigation of the Las Vegas Valley Evaluating Response (SILVVER) experiment, performed in August 2003, into a 3-D crustal velocity model.
DE: 7205 Continental crust (1242)
DE: 7223 Seismic hazard assessment and prediction
DE: 8015 Local crustal structure
SC: Seismology [S]
MN: 2003 Fall Meeting