HR: 14:15h
AN: G23C-04    [Abstracts]
TI: Anomalous geodetic dilatation at the Central Nevada Seismic Belt: Inferring secular and transient contributions
AU: * Hammond, W C
EM: whammond@unr.edu
AF: Nevada Geodetic Laboratory, Nevada Bureau of Mines and Geology/Mail Stop 178, Reno, NV 89557-0088 United States
AU: Kreemer, C
EM: kreemer@unr.edu
AF: Nevada Geodetic Laboratory, Nevada Bureau of Mines and Geology/Mail Stop 178, Reno, NV 89557-0088 United States
AB: The Basin and Range province of the western United States exhibits distributed contemporary extensional and transtensional faulting. Near the western edge of the province a sequence of large historic (M6.8-M7.5) earthquakes occurred in a belt that roughly follows the regional trend in faulting and topography. This alignment of ruptures, known as the Central Nevada Seismic Belt (CNSB), exhibits significantly elevated geodetic extension compared to its surroundings. If interpreted solely as secular strain, the geodetic extension implies fault slip rates that are over a factor of two greater than rates inferred from paleoseismology. If interpreted solely as post-seismic viscoelastic relaxation of the lower crust and upper mantle, then this implies that secular strain rates are near zero, which would underestimate geologic rates. Additionally, the CNSB resides in an area that makes this distinction difficult. East of the CNSB geodetic strain rates are almost indistinguishable from zero, but in the northern Walker Lane to the west, the strain rates are among the highest in the province. Because it lies near this boundary, it is not clear whether the CNSB should behave more like the Great Basin or the Walker Lane. Distinguishing how much of this extension is locally due to faster slip rates on faults versus post-seismic processes is central to understanding regional crustal kinematics, rheological stratification of the Basin and Range lithosphere, and to quantifying seismic hazard in the region. We consider the two end-member cases discussed above in order to develop models that are consistent with geodetic, seismological and geological observations. The first explains tectonic horizontal geodetic extension with interseismic loading of locked normal faults whose pattern is a measure of the long-term slip rate on the fault. The second explains all deformation with post-seismic transients following a recent normal faulting event. We iterate over a large number of possible rheological structures, varying the lower crustal and upper mantle viscosity, generating predicted geodetic velocities and strain rates. We then evaluate the misfit of the data to the predicted velocities and strains rates to find the most likely rheological structures. To estimate an intermediate model, we subtract a model of secular strain that is consistent with the paleoseismologically inferred slip rates from the geodetic data. These models are constrained by a regional compilation of horizontal Global Positioning System velocities, a strain rate model inferred from these velocities, and a compilation of paleoseismic and seismological data for the historic and pre-historic earthquakes at the CNSB.
DE: 1208 Crustal movements--intraplate (8110)
DE: 7221 Paleoseismology
DE: 8109 Continental tectonics--extensional (0905)
DE: 8159 Rheology--crust and lithosphere
SC: Geodesy [G]
MN: 2005 Joint Assembly