FRACTURE ANALYSIS OF RELAY ZONE ARCHITECTURE ALONG THE SOUTHERN SIERRA NEVADA FRONTAL FAULT ZONE

The Sierra Nevada Frontal Fault Zone (SNFFZ) is a ~640 km long southeast-northwest trending, normal fault array that bounds the eastern flank of the Sierra Nevada Mountains in eastern California, USA. The SNFFZ is located along the western boundary of both the Basin and Range Province and the Walker Lane Belt. While the Walker Lane Belt accommodates a significant portion of Pacific-North American plate motion, SNFFZ structures have experienced primarily dip-slip displacement. Offset of Quaternary landforms such as glacial moraines and alluvial fans yield slip rates of 0.1-0.3 mm/yr. These data constrain short-term displacement at specific locations but provide little to no information about the long-term evolution of the fault array. Patterns of footwall exhumation, obtained from multiple low-temperature thermochronometers, can be used to resolve the timing of fault linkage and constrain long-term fault displacement profiles. An in depth understanding of fault system architecture is required, however, to accurately interpret the thermochronometric data. Isolated normal faults propagate laterally through the coalescence of fractures within damage zones surrounding fault tips. In a normal fault array, the local stress field associated with individual faults may communicate with that of neighboring faults. Fractures developed within this zone of interaction record the progression from isolated fault segments to a single, mechanically linked fault. These fractures may be preserved while subsequent fault displacement, footwall erosion, and basin sediment obscure evidence of fault interaction and linkage. West of Owens Lake is a left step in the Eastern Sierra Nevada rangefront that may represent a mature relay zone between segments of the SNFFZ. This hypothesis is currently being tested by characterization of fracture networks in the area using field mapping, orthophoto interpretation, and GIS analyses. Future work will incorporate low-temperature thermochronometry (Apatite Fission Track and (U-Th)/He) along fault-parallel and vertical transects, to determine the pattern of footwall denudation and constrain the long-term evolution of the SNFFZ.