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kreemer

HR: 11:05h
AN: G52A-04 INVITED
TI: Postseismic Relaxation at the Central Nevada Seismic Belt Observed in Vertical GPS Time Series
AU: * Hammond, W C
EM: whammond@unr.edu
AF: Nevada Bureau of Mines and Geology and Nevada Seismological Laboratory, University of Nevada, Reno, Reno, NV 89557-0178, United States
AU: Plag, H
EM: hpplag@unr.edu
AF: Nevada Bureau of Mines and Geology and Nevada Seismological Laboratory, University of Nevada, Reno, Reno, NV 89557-0178, United States
AU: Blewitt, G
EM: gblewitt@unr.edu
AF: Nevada Bureau of Mines and Geology and Nevada Seismological Laboratory, University of Nevada, Reno, Reno, NV 89557-0178, United States
AU: Kreemer, C
EM: kreemer@unr.edu
AF: Nevada Bureau of Mines and Geology and Nevada Seismological Laboratory, University of Nevada, Reno, Reno, NV 89557-0178, United States
AB: Between 1872 and 1954 the Basin and Range province of the western United States experienced six major earthquakes that occurred in a quasi-linear belt known as the Central Nevada Seismic Belt (CNSB). These strike-slip to normal events account for most of the seismic moment release that has occurred in the Basin and Range in historic time. Several studies have noted the possible presence of a contemporary geodetic signal owing to postseismic relaxation from these earthquakes, implying that this signal has persisted for decades after the events. Observations that support the existence of this postseismic signal are: 1) GPS-derived horizontal strain rates that are relatively high compared to the surrounding regions, 2) 3-4 mm/yr vertical upward doming observed with Interferometric Synthetic Aperture Radar (InSAR) that is consistent with models of viscoelastic relaxation of the mantle, 3) possible rapid vertical postseismic motion observed using leveling measurements immediately following the 1954 events, 4) disagreement between geodetically and geologically inferred strain rates that is consistent with elevated contemporary transient strain. Since 2004 the University of Nevada, Reno has operated a semi-continuous GPS network with ~20 km spacing (the Mobile Array of GPS for Nevada Transtension: MAGNET) that complements the spatially less dense Basin and Range Geodetic Network (BARGEN) and Plate Boundary Observatory (PBO) continuously recording networks. MAGNET is ideally deployed to observe the ongoing transient deformation associated with the central Nevada earthquake cycle because it spans the CNSB faults where the predicted postseismic signal is greatest. We analyze the GPS data with the GIPSY/OASIS II software package in precise point positioning and apply regional filtering to remove common mode effects (uniform displacements and/or rotations that are present in all the time series). These common mode signals have a much larger impact on the vertical than on horizontal rates, especially for shorter time series, so accounting for them is essential for studying vertical motions with GPS. The filtered time series enhance our resolution of the relative vertical motion between sites. Our preliminary results based on 2.5-3.3 years of GPS data from MAGNET indeed detect a horizontal gradients in the vertical rates of 3 - 4 mm/yr that is consistent with earlier studies based on InSAR and campaign GPS. We find that the MAGNET sites directly east of Dixie Valley (in the Clan Alpine Range) have the greatest vertical uplift rate, suggesting that the 1954 Dixie Valley earthquake makes a larger contribution to the contemporary uplift than the other earthquakes associated with the CNSB. The largest amplitudes in the vertical signal appear to be limited to the MAGNET sites, highlighting the need for arrays denser than provided by the continuous networks (i.e. PBO and BARGEN) in this region.
UR: http://geodesy.unr.edu/networks
DE: 1207 Transient deformation (6924, 7230, 7240)
DE: 1240 Satellite geodesy: results (6929, 7215, 7230, 7240)
DE: 1242 Seismic cycle related deformations (6924, 7209, 7223, 7230)
DE: 7209 Earthquake dynamics (1242)
DE: 8109 Continental tectonics: extensional (0905)
SC: Geodesy [G]
MN: 2007 Fall Meeting