HR: 1340h
AN: G53A-0874    [Abstracts]
TI: Time-Dependent Motion of Slide Mountain, Western Nevada, 1997-2005
AU: * Davis, J L
EM: jdavis@cfa.harvard.edu
AF: Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 United States
AU: Wernicke, B P
EM: brian@gps.caltech.edu
AF: California Institute of Technology, Division of Geological and Planetary Sciences 170-25 1200 E. California Blvd., Pasadena, CA 91125 United States
AU: Bisnath, S
EM: sbisnath@cfa.harvard.edu
AF: Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 United States
AU: Niemi, N
EM: niemi@gps.caltech.edu
AF: California Institute of Technology, Division of Geological and Planetary Sciences 170-25 1200 E. California Blvd., Pasadena, CA 91125 United States
AB: The horizontal position of the Slide Mountain site (SLID) of the Basin and Range Geodetic Network (BARGEN) has presented anomalously high horizontal variability since its construction in 1997. Its weighted root-mean-square east and north position components, relative to best-fit straight lines, are a factor of ~2 greater than surrounding BARGEN sites that use the same type of deeply anchored monuments. Smith et al. [ Science, 2004] reported a large transient in the northeast position of SLID of ~6 mm (and ~8mm upward) in late 2003 that was coeval with a swarm of deep, low magnitude earthquakes at Lake Tahoe, 18~km away from SLID. They tentatively concluded that the seismic events and the geodetic displacement of SLID are associated with lower-crustal magma injection near Lake Tahoe. We have analyzed the entire time series for SLID, and discovered that the anomalous position variability is best understood as continual large motions along a northeast-southwest axis (N59°± 7°E). The position variations along the perpendicular direction are much smaller and consistent with those of the other BARGEN sites. We have investigated the possibility of three ``error'' processes that might explain the observed motions: (1) antenna element failure; (2) crustal loading due to variations in Lake Tahoe water level; and (3) crustal loading due to Sierran snow accumulation. None of these processes explain the observed motions, although the direction of loading signals is consistent with the estimated axis of motions. The cumulative non-linear geodetic site displacement of SLID over the eight years of observation is consistent with those of the other GPS sites in the western Basin and Range, suggesting that the SLID motion is revealing a local aspect of a spatially larger-scale process that induces small, but geodetically important, decade-scale transient motions.
DE: 1207 Transient deformation (6924, 7230, 7240)
DE: 1211 Non-tectonic deformation
DE: 8109 Continental tectonics: extensional (0905)
SC: Geodesy [G]
MN: Fall Meeting 2005