HR: 16:20h
AN: H34B-02 INVITED     [Abstracts]
TI: Geomorphic Expression and Neotectonic Evaluation of a Diffuse Fault System from Airborne Laser Swath Mapping, Pahrump Valley, California and Nevada
AU: Niemi, N
EM: niemi@gps.caltech.edu
AF: Division of Geological and Planetary Sciences, California Institute of Technology 1200 E. California Blvd., Pasadena, CA 91125 United States
AU: * Guest, B
EM: bguest@gps.caltech.edu
AF: Division of Geological and Planetary Sciences, California Institute of Technology 1200 E. California Blvd., Pasadena, CA 91125 United States
AU: Wernicke, B
EM: brian@gps.caltech.edu
AF: Division of Geological and Planetary Sciences, California Institute of Technology 1200 E. California Blvd., Pasadena, CA 91125 United States
AB: The eastern boundary of the Eastern California shear zone (ECSZ) is defined by the Stateline-Amargosa Valley fault zone (SAVFZ), a NW striking zone of dextral faulting that extends 150 km along the CA-NV border in Clark and Nye counties. This fault system has accumulated ~ 30 km of slip since 12.5 Ma, yielding a long-term slip rate of ~ 2 mm/yr. This rate is twice the modern rate, as estimated from GPS data in the region (Wernicke et al., 2004, JGR). A comparison of modern and long-term slip rates on the SAVFZ with Quaternary slip rates is desirable, both to understand the evolution of the ECSZ, and to assess the risk of the SAVFZ to the proposed high-level nuclear waste repository at Yucca Mountain, but is hampered by a lack of well-defined Quaternary offsets. Both the position of the SAVFZ relative to adjacent mountain ranges and the nature of faulting within the SAVFZ contribute to this problem. Rather than being located at the boundary between ranges and basins, the SAVFZ runs axially through four basins. Instead of cutting alluvial deposits that uphold a fault scarp, the SAVFZ tends to be developed within incompetent lacustrine units. The SAVFZ is composed of a series of discontinuous, en echelon fault strands, rather than being a discrete fault surface. This fault system, therefore, has a subtle geomorphic expression, a factor which has been interpreted as a lack of neotectonic activity. To remedy this problem, ALSM data were collected along the SAVFZ in Pahrump Valley. Data collected parallel to the SAVFZ reveal a large number of previously unrecognized geomorphic offsets and the complex, anastamosing nature of the fault zone, many of which are difficult or impossible to identify via field surveys alone. Channels in southern Stewart Valley observed in the ALSM data are offset 30 to 70 m, presumably since early Holocene time (dePolo et al., 2003, NBMG OFR 03-11), yielding slip rates of 5 to 10 mm/yr. These rates are difficult to reconcile with the modern slip rate on the SAVFZ estimated from GPS data, and require further investigation. The observed offsets underscore the importance of ALSM data in quantitatively assessing neotectonic motion along subtly expressed fault systems.
DE: 1625 Geomorphology and weathering (0790, 1824, 1825, 1826, 1886)
DE: 8002 Continental neotectonics (8107)
DE: 8036 Paleoseismology (7221)
DE: 8040 Remote sensing
SC: Hydrology [H]
MN: Fall Meeting 2005