HR: 0830h
AN: S11D-0328    [PDF]
TI: Using Precision Gravity Survey To Locate Faults Within The Southern Mesilla Bolson, Rio Grande Rift.
AU: * Khatun, S
EM: khatun@geo.utep.edu
AF: Department of Geological Sciences, University of Texas at El Paso., 500, University Av., El Paso, Tx 79968
AU: Doser, D
EM: doser@geo.utep.edu
AF: Department of Geological Sciences, University of Texas at El Paso., 500, University Av., El Paso, Tx 79968
AU: Imana, E
AF: Department of Geological Sciences, University of Texas at El Paso., 500, University Av., El Paso, Tx 79968
AB: The southern Mesilla bolson of west Texas and southern New Mexico is a rapidly growing portion of the El Paso-Juarez metropolitan area. Faulting within the bolson is difficult to trace due to intensive urban and agricultural activities. Prior to channelization of the Rio Grande in the 1930's the river also frequently altered its course, rapidly depositing or eroding sediment within the bolson, also making the tracing of faults or offset surfaces difficult. We have used the precision gravity technique (digital precision gravity meter, station spacing of 60 m or less, elevation known to 30 cm or less) as an inexpensive method to map possible locations of faults within the bolson. We analyze the gravity data using 3-D modeling techniques that can account for known geology and topography, which are then subtracted from the observed gravity data. The residual gravity map is then examined for sharp gradients and bends in gravity contours that may indicate the presence of faults. Once suspected faults are identified we have conducted follow-up geophysical surveys (DC resistivity sounding, spectral analysis of surface waves) over the structures to determine if grain size or sediment compaction changes (often indicative of faults) are associated with the gravity anomalies. Water well logs have also aided in our interpretations. Our results suggest there are at least 3 faults within the bolson that parallel the range bounding fault that separates the eastern bolson from the western edge of the Franklin Mountains. If these faults are currently seismogenic, they represent a significant hazard to the urban areas located on the thick (1500 m), water saturated sediments of the bolson. We feel the precision gravity technique could serve as a useful reconnaissance tool to help identify faults in other regions where urbanization or other factors limit surface exposure of recent geologic processes.
DE: 1219 Local gravity anomalies and crustal structure
DE: 7200 SEISMOLOGY
DE: 7223 Seismic hazard assessment and prediction
SC: Seismology [S]
MN: 2003 Fall Meeting