HR: 17:15h
AN: S34A-06    [Abstracts]
TI: Crustal Velocity Model of Watusi Data Integrated With Legacy Data, Clark County, Nevada
AU: * Zaragoza, S A
EM: szargo@physics.unlv.edu
AF: University of Nevada Las Vegas, 4505 Maryland Parkway, Las Vegas, NV 89154 United States
AU: Snelson, C M
EM: csnelson@unlv.nevada.edu
AF: University of Nevada Las Vegas, 4505 Maryland Parkway, Las Vegas, NV 89154 United States
AB: The Las Vegas Valley, Nevada is located in the central Basin and Range Province, about 100 km southeast of the Nevada Test Site (NTS). Las Vegas sits atop a basin up to 5 km deep (Langenheim et al., 2001) that has been shown to amplify energy from strong ground motion (Su et al., 1998). Rapid population growth has led to concerns that future nuclear testing at NTS may pose a hazard from strong ground motion. Studies performed when nuclear testing was ongoing were limited to the central basin and were insufficient to adequately assess ground motion hazard for the entire Valley. In September 2002, 400 single-channel seismic recorders were deployed to record a chemical blast (Watusi) at NTS. Forward modeling of these data as well as Legacy data from the 1960s (Prodehl, 1979) produced a 268 km two-dimensional crustal velocity model from Kingman, Arizona to NTS with higher resolution than the previous model. Crustal velocities range from 3.5 to 6.2 km/s. Velocities at the Moho range from 7.9-8.0 km/s. Crustal depth ranges from 28-29 km near Kingman to 33-34 km near NTS. A structural feature in model space at 12-15 km underneath Indian Springs, Nevada appears to focus seismic energy into the Las Vegas basin, and may pose a significant seismic hazard. The feature has a dip in model space of 45§ toward the southeast. A density model was also produced and tied to the velocity model. The density model is consistent with the velocity model, confirming crustal depth ranges from 28-29 km near Kingman to 33-34 km near NTS. The density model also confirms the 45§ southeast-dipping structural feature and indicates the location of a mafic body in model space at a depth of 5-12 km beneath the Las Vegas Basin. Possible interpretations of the dipping structure include a relict thrust or metamorphic core complex. However, these interpretations are difficult due to the steep dip angle of the feature, and more evidence would be needed to verify one of these conclusions. A more likely interpretation would be that this feature represents apparent dip on the Las Vegas Valley Shear Zone.
DE: 7223 Seismic hazard assessment and prediction
DE: 8015 Local crustal structure
DE: 7205 Continental crust (1242)
SC: Seismology [S]
MN: 2004 AGU Fall Meeting