HR: 14:40h
AN: S53C-05    [Abstracts]
TI: Calibration and Interpretation of GPR Images across a Northern Basin and Range Normal Fault Scarp, Crescent Valley, Nevada, USA.
AU: * Lazaro-Mancilla, O
EM: olazaro@iing.mxl.uabc.mx
AF: Instituto de Ingenieria, UABC., Blvd. Benito Juarez y Calle de la Normal S/N., Mexicali, BC 21280 Mexico
AU: Friedrich, A M
AF: Institut fur Geowissenschaften, Karl-Liebknecht-Str. 24, Golm, D-14476 Germany
AB: We present results from GPR imaging and paleoseismological mapping of a trench across the active trace of the Crescent Valley normal fault, NV. The two data sets provide consistent and detailed images of individual fault splays, offset marker beds, and alluvial deposits. The Crescent Valley normal fault is one of the most active normal faults of the northern Basin and Range province. Prominent 2 11 m high scarps formed in alluvial deposits at most canyon mouths. At Fourmile Canyon, the fault scarp is $\sim$5m high and cuts an abandoned late Holocene alluvial surface (locally referred to as Qf2). Trenching results imply that this scarp formed during a single earthquake at $\sim$2.7 ka. The Qf2 alluvial fan consists of stratified granule- to cobble-size gravel deposits and interbedded gravel, sand, silt and clay layers. The clasts consist of silicious material, such as shale, chert, quartz-monzogranite, basalt, and diorite. The excavated pit was over 6 m deep and did not perch the water table. In the hanging wall, the pre-faulting surface (Qf2) is covered by scarp-derived colluvial gravel deposits and a silt layer, which in turn is overlain unconformably by alluvial gravel deposits (Qf3). To image the faults and stratigraphic contacts exposed in the trench, we used a EKKO 100 GPR system for near surface surveys with common-offset, to run single fold reflection profiles at 50, 100, and 200 MHz and CMP surveys on lines parallel to both sides of the trench. The GPR images were compared with trench logs for calibrate it. Our comparison of GPR data with data trench, permit us conclude that 50 MHz GPR data give us the better image related with the splay faults at depth and the 100 MHz images were useful for delineate minor features of faults offsets but were limitated by the penetration depth of the GPR. With this calibration we interpreted a profile surveyed in other area of this site and could image the fault there.
DE: 8010 Fractures and faults
DE: 6982 Tomography and imaging
DE: 0634 Measurement and standards
DE: 0689 Wave propagation (4275)
DE: 0694 Instrumentation and techniques
SC: Seismology [S]
MN: 2004 AGU Fall Meeting