HR: 0830h
AN: S11D-0324    [PDF]
TI: Geologic Interpretation of the Las Vegas Valley Based on Industry Seismic Reflection Data
AU: * Hirsch, A
EM: achirsch@csbsju.edu
AF: St. John's University/College of St. Benedict, Department of Geology; Pengle Science Center, Collegeville, MN 56321 United States
AU: Snelson, C M
EM: csnelson@unlv.nevada.edu
AF: Univeristy of Las Vegas Nevada, Department of Geoscience, University of Nevada Las Vegas, 4505 Maryland Pkwy, MS 4010, Las Vegas, NV 89154-4010 United States
AB: Las Vegas Valley, NV is located in the southern Basin and Range Province where the basin was formed by the Las Vegas Valley Shear Zone as well as by several thrust and normal faulting events that occurred by Cenozoic time. The geology and tectonic setting in the Las Vegas region is poorly understood given the fact that many structures have been covered by the constant growth of the City. National studies of ground motion and amplification of seismic energy placed Nevada third in the list of states having the potential for loss of life and property due to earthquakes. The Las Vegas area has a high potential for strong ground shaking due its thick basin fill and associated amplification. Due to the amplification effects within the Valley, moderate nearby quakes or large distant quakes will produce a large amount of damage in the Valley. Las Vegas, though not known for its earthquakes, has numerous micro quakes and an active seismic history. In a study using HAZUS to predict damage associated with a M6.9 earthquake, the loss would be billions of dollars with thousands of lives lost. Long-term economic loss would be in the several billions of dollars. Recently, several normal faults, which have the potential to produce a M6.5 to 7.0 earthquake, were reclassified as active tectonic fault with Quaternary movement. As a result, there has been increased effort to understand the Las Vegas Valley and to assess its potential for seismic hazards. One such effort included acquiring industry reflection profiles that cross the Valley. In the 1980's, north/south and east/west trending reflection lines with intersecting tie points were placed between Frenchman Mountain to the East and Spring Mountains to produce seismic profiles using Vibroseis. The profiles, which are over 200 kilometers in length and extend down to 5 s in time or approximately 15 km depth, will provide a tie between the surface work that is currently being conducted and the crustal velocity models that are being calculated to produce a seismic hazard potential for the Las Vegas Valley. The quality of the Vibroseis data is very high. We have been able to locate the basin/bedrock contact as well as several faults that cut the sections. All of which have been mapped on the shot point map. Most of the faults appear to be normal faults listric in character that trend north-south paralleling the structure of the southern Basin and Range. Basin geometry and associated minor folding, which have been truncated by minor faulting, can be seen across the profiles. Some faults can be seen as tectonic in origin while others are merely subsidence faulting from basin settling. With this new data we will identify structures that could potentially focus energy in the sub-surface adding to our growing knowledge of the basin geometry. In addition, this data will be incorporated into the seismic hazard model that is being developed for the Las Vegas Valley and will provide very detailed geologic information that has not been previously available.
DE: 7200 SEISMOLOGY
DE: 7223 Seismic hazard assessment and prediction
SC: Seismology [S]
MN: 2003 Fall Meeting