HR: 0800h
AN: T41F-1288    [Abstracts]
TI: Evidence for Quaternary Slip on a Low Angle Normal Fault: Searles Valley, CA
AU: * Numelin, T
EM: tnumelin@geosc.psu.edu
AF: The Pennsylvania State University, Department of Geoscience, University Park, PA 16802 United States
AU: Kirby, E
EM: ekirby@geosc.psu.edu
AF: The Pennsylvania State University, Department of Geoscience, University Park, PA 16802 United States
AB: Low angle normal faults have been documented in extensional terranes worldwide, however conventional models of fault mechanics preclude slip on planes dipping less than 30 degrees. The global catalogue of earthquake focal mechanisms reveals very few occurrences of seismicity (active slip) on low angle structures, lending support to mechanical arguments against active slip on shallowly dipping planes. Recent field studies of low-angle normal faults in the Baja California and Death Valley regions of western North America, however, suggest that active slip on these structures may be more common than typically thought. Here we investigate the relationship between high angle alluvial scarps in Searles Valley and a low-angle detachment fault in order to determine if displacement on the detachment is active. The network of young and recent fault scarps along the eastern margin Searles Valley can be broadly separated into two primary segments with overlapping fault tips that form a range-scale relay zone in the vicinity of Sand Canyon. South of this relay, the active trace of the fault is marked by a series of graben developed within Late Pleistocene - Holocene alluvial fans. Within the bedrock of the Slate Range, and immediately along-strike of the graben system, is a west dipping, low-angle fault system (Sand Canyon `thrust' - Smith et al., 1968). This fault is continuous within the range for some 20 km and links with a west-dipping normal fault near Manly Pass, and is thus thought to have accommodated west directed normal-sense displacement during Plio-Quaternary time (Andrew and Walker, 2002). Mapping and structural observations at the intersection of the active fault system and the Sand Canyon fault reveals that high-angle scarps cutting Pleistocene alluvium root into a low-angle (10-15ø), west-dipping gouge zone. Faults do not significantly displace the detachment surface, and thus, scarp-forming displacement must have been accommodated by slip on the detachment itself. We combine high-precision differential GPS surveys of fault displacement with existing chronology gleaned from a range of Late Pleistocene - Holocene lacustrine deposits related to Searles Lake to develop estimates of fault slip rate along the length of the fault system. Slip rates provide insight into both the local question of how slip is partitioned across the Sand Canyon relay zone, as well as the more regional question of how deformation within the Eastern California Shear Zone is accommodated.
DE: 8107 Continental neotectonics
DE: 8109 Continental tectonics--extensional (0905)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting