HR: 0800h
AN: G51B-0815    [Abstracts]
TI: Detecting and Imaging Aseismic Transient Deformation in Southern California
AU: * Liu, Z
EM: liuz@pangea.stanford.edu
AF: Department of Geophysics Stanford University, 397 Panama Mall, Stanford, CA 94305 United States
AU: Segall, P
EM: segall@pangea.stanford.edu
AF: Department of Geophysics Stanford University, 397 Panama Mall, Stanford, CA 94305 United States
AB: Large-scale continuous GPS networks have documented a wide-range of aseismic deformation transients resulting from various physical processes, including aseismic fault slip and magma intrusion. Recently, a variety of transient slip events have been discovered in subduction zone environments. Previously, transient slip episodes were identified along the San Andreas Fault near transitions from creeping to locked segments of the fault. The Southern California Integrated GPS Network (SCIGN) provides the possibility to explore for these and other aseismic deformation transients in a major strike-slip plate boundary setting. We are applying the Extended Network Inversion Filter (ENIF) of (McGuire and Segall, Geophys. J. Int, 2003), a time-dependent inversion algorithm based on an extended Kalman filter to search for possible aseismic transient slip signals in Southern California. The ENIF is able to separate signals from various processes and image spatial-temporal evolution of the slow-slip events in detail. We extended the method to include triangular-mesh surfaces by introducing triangular dislocations and spatial smoothing on triangular fault surface. The new filter version (named TNIF) enables us to incorporate complex 3-dimensional fault geometry. We construct a fault model using SCEC Community Fault Model (CFM). Slip rates from USGS/CGS2002 fault database and geometry from the SCEC Community Fault Model are combined. To regularize the surface mesh while reducing the number of inversion parameters, we remeshed all faults of the CFM with slip rate >= 2.0mm/yr onto coarser grids by applying point/boundary constraints and isotropic DSI interpolation. Raw SINEX solutions from Scripps Orbit and Permanent Array Center (SOPAC) are used in a differential sense in the inversion. The time series are cleaned by removing offsets and outliers identified by SOPAC. To date we have applied the TNIF to the area 30km from the fault San Andreas Fault (74 sites), using data from January 2001 to June 2005. Postseismic deformation following Sep. 28, 2004 Mw6.0 Parkfield Earthquake is easily identified and reasonably well modeled. The filter identifies other areas of transiently high slip rate, however these regions are dominated by a few sites and require further study. We are currently in the process of including more faults and GPS stations into our inversion filter and exploring transient signals on other faults of southern California.
DE: 1207 Transient deformation (6924, 7230, 7240)
DE: 1242 Seismic cycle related deformations (6924, 7209, 7223, 7230)
DE: 1243 Space geodetic surveys
DE: 7223 Earthquake interaction, forecasting, and prediction (1217, 1242)
DE: 8107 Continental neotectonics (8002)
SC: Geodesy [G]
MN: Fall Meeting 2005