HR: 13:40h
AN: G53A-01    [Abstracts]
TI: Variations in Creep Rate along the Central San Andreas Fault from InSAR and GPS Observations
AU: * Ryder, I M
EM: isabelle@seismo.berkeley.edu
AF: UC Berkeley, 215 McCone Hall, Berkeley, CA 94704, United States
AU: Burgmann, R
EM: burgmann@seismo.berkeley.edu
AF: UC Berkeley, 215 McCone Hall, Berkeley, CA 94704, United States
AB: The San Andreas Fault is locked along most of its length, but the 170 km-long section between San Juan Bautista and Parkfield undergoes creep. Measurements from creepmeters, alignment arrays and GPS over the last 25 years have shown that surface creep rates reach about 30 mm/year in the central portion, tapering off towards the locked segments at either end. Though useful, these measurements have been spatially isolated and intermittent in time. We present InSAR observations of creep across the fault, which have superior spatial coverage than previous data, and analyse them to investigate spatial variations in creep rate along the fault segment. From multiple ERS-1 and ERS-2 descending interferograms covering 1992 to 2001, we produce a stack which gives the spatial distribution of creep rate up to about 50 km either side of the fault. We find a maximum creep rate of about 32 mm/year. Deformation is step-like most of the way along the segment, but more distributed at the northern end, where the Calaveras Fault comes very close to the San Andreas Fault. We perform a linear inversion for shallow and deep sliding velocity on these faults using both the InSAR stack and GPS velocities from continuous (PBO) and campaign networks. Creep in the top few kilometers is variable along strike, with patches of faster creep interspersed with more slowly-moving patches. Creep at intermediate depths is greatest in the centre of the segment, reaching a few mm/yr less than the relative plate rate. The deep (> 12 km) sliding velocity is constrained to be less than or equal to the estimated long term relative plate velocity, and we estimate it to be a few mm/yr less than this. We compare the depth-averaged creep rate profile along the fault segment with that estimated by Nadeau and McEvilly (2004) from characteristic repeating microearthquakes. Between them, the three datasets utilised in this study suggest that creep is a spatially heterogeneous process.
DE: 1209 Tectonic deformation (6924)
DE: 1240 Satellite geodesy: results (6929, 7215, 7230, 7240)
DE: 8004 Dynamics and mechanics of faulting (8118)
DE: 8111 Continental tectonics: strike-slip and transform
SC: Geodesy [G]
MN: 2007 Fall Meeting