HR: 11:35h
AN: T22A-06    [Abstracts]
TI: A Potential Reconciliation of Short-Term Geodetic and Long-Term Geological Strain-Rate Estimates Across the Owens Valley
AU: * Phillips, F M
EM: phillips@nmt.edu
AF: New Mexico Tech, Department of Earth and Environmental Science 801 Leroy Place, Socorro, NM 87801, United States
AU: Kirby, E
EM: ekirby@geosc.psu.edu
AF: Pennsylvania State University, 336 Deike Bldg. Department of Geosciences, University Park, PA 16802, United States
AU: Anadakrishnan, S
EM: sak@geosc.psu.edu
AF: Pennsylvania State University, 336 Deike Bldg. Department of Geosciences, University Park, PA 16802, United States
AU: Marrero, S M
EM: shasta@nmt.edu
AF: New Mexico Tech, Department of Earth and Environmental Science 801 Leroy Place, Socorro, NM 87801, United States
AB: Geodetic data show a distinctive pattern of modern strain-rate across the southwestern Great Basin (between 36° and 38° N). Strain rates are low in the interior of the Basin and in the Sierra Nevada block, whereas they are large immediately east of the Sierra Nevada. A compilation of GPS velocities indicates an average displacement rate of the Sierra Nevada block relative to the White/Inyo Mountain block of 4.1±0.8 mm yr^-1 directed 305°±6°. This value constitutes approximately 25 percent of the total strain between the North American craton and the Sierra Nevada. A value this large is in apparent conflict with the results of paleoseismic studies that indicate slip rates on the Owens Valley Fault Zone (OVFZ), and associated dip-slip faults, are too low to accommodate this rate of divergence. It also conflicts with mechanical models of faulting that show that sufficient slip on high-angle normal faults to permit this rate of displacement would produce a much greater depth to bedrock than is actually observed in the Owens Valley. We have investigated the long-term slip rate on the OVFZ by using ground-penetrating radar to determine the margin of a lava flow at Crater Mountain that is dextrally offset by the fault, and hence the total displacement of the flow. We have used cosmogenic ³⁶Cl to determine an eruption age of 68±12 ka, yielding a slip rate over this time that averages between 2.8 and 4.5 mm yr^-1. In contrast to previous studies over much shorter time scales, this rate is in general agreement with that from geodetic measurements. We further propose that displacement on both strike-slip and normal, valley-bounding faults is integrated into relatively uniform regional transtensional strain by means of extensive low-angle faults underlying the Owens Valley. Displacement on listric valley-bounding faults permits significant extension without requiring vertical displacements in excess of observations. These new data and observations support the inference, based on short-term geodetic measurements, that much of the total strain between the Colorado Plateau and the southern Sierra Nevada is, and has been, accommodated in a relatively narrow band east of the Sierra Nevada.
DE: 8107 Continental neotectonics (8002)
DE: 8109 Continental tectonics: extensional (0905)
DE: 8111 Continental tectonics: strike-slip and transform
DE: 8175 Tectonics and landscape evolution
DE: 9350 North America
SC: Tectonophysics [T]
MN: 2007 Fall Meeting