HR: 1340h
AN: G13A-0926    [Abstracts]
TI: The Acceleration Gradient Tensor Field in Southern California Estimated using Continuous SCIGN GPS Data
AU: Hernandez, D
EM: danherna@ic.sunysb.edu
AF: Department of Geosciences, 255 Earth and Space Sciences Building, Stony Brook University, Stony Brook, NY 11794, United States
AU: * Holt, W E
EM: william.holt@sunysb.edu
AF: Department of Geosciences, 255 Earth and Space Sciences Building, Stony Brook University, Stony Brook, NY 11794, United States
AU: Bennett, R A
EM: rab@geo.arizona.edu
AF: Department of Geosciences, University of Arizona, Gould-Simpson Bldg. #77, Tucson, AZ 85721-0077, United States
AU: Haines, A J
EM: ajh50@cam.ac.uk
AF: Department of Earth Sciences, University of Cambridge, Downing St., Cambridge, CB2 3EQ, United Kingdom
AB: We use the continuous SGIGN GPS network between the periods of late 1999 to 2004 (post-Hector Mine) to measure the acceleration gradient tensor field in southern California. We first interpolate the continuous time series with fourth-order polynomials, which have proven stable and capable of capturing first-order temporal variations within the time series. Annual and semi-annual signals are removed. We use Monte-Carlo simulations to estimate the model uncertainties in the time-dependent velocities and accelerations inferred from the continuous GPS time series. Once model continuous acceleration estimates are inferred for all stations, we interpolate the acceleration estimates within a 0.1° x 0.1° finite element grid in southern California using the method of Beavan and Haines [2001]. Boundary conditions of zero acceleration are used at the edges of the region considered. West of the Hector Mine rupture, during the first six months following the Hector Mine event, acceleration vectors show a large clockwise rotational pattern, with acceleration rates of 3 - 10 mm yr^-2 for stations south of the San Jacinto Fault and east of the Los Angeles Basin. Significant rates of change of the strain rate tensor field in the first year following the Hector Mine event occur in the Hector Mine region, the region of Los Angeles Basin, and areas both south and west of the southern San Andreas Fault. Within the first year of the Hector Mine event, time rates of change of strike slip shear strain rates of order 1x10^-7 yr^-2 occur around the Hector Mine rupture, whereas rates of change of dilatational strain rate around the Hector Mine event (3-5x10^-8 yr^-2) occur over a much larger region surrounding the rupture zone. During this time period there are also large contractional rates of change of dilatational strain rates along the San Jacinto fault zone (- 3x10^-8 yr^-2) and both tensional and contractional rates of change of dilatational strain rate within the greater Los Angeles region (4-5x10^-8 yr^-2). The patterns of spatially variable accelerations following the Hector Mine rupture are related to the elastic response of the rupture but also suggest highly variable crustal properties that result in an inhomogeneous response and recovery associated with the Hector Mine event.
DE: 1207 Transient deformation (6924, 7230, 7240)
DE: 1209 Tectonic deformation (6924)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 8111 Continental tectonics: strike-slip and transform
DE: 8159 Rheology: crust and lithosphere (8031)
SC: Geodesy [G]
MN: 2007 Fall Meeting