Frederique Rolandone *, Ingrid Johanson ** , Eric Fielding *** , Roland Bürgmann ** ,

1. GAMIT/GLOBK processing 0.15 micro-strain/yr BaVu , Matt d’Alessio (UCB) Continuous GPS (University of Wisconsin) SCEC CMM3.1 Creepmeters SIO, SCIGN Our new campaign measurements Observed Predicted LOS mm XSC1 6/23/04-12/15/04 9/14/04-11/23/04 mm Variations in aseismic slip along the creeping section of the San Andreas Fault from space-geodetic data Frederique Rolandone*, Ingrid Johanson**, Eric Fielding***, Roland Bürgmann**, *UPMC, Paris, **Dept. of Earth and Planetary Science, UC Berkeley, ***JPL, Pasadena In central California most of the relative motion between the Pacific and North American plates is accommodated by strike slip along the San Andreas fault system. Along the central San Andreas fault (CSAF), from San Juan Bautista to Parkfield, almost all the slip along the CSAF in the brittle upper crust is accommodated aseismically. We use GPS, InSAR and trilateration data to resolve both the distribution of aseismic slip along the CSAF, and the deformation across adjacent, secondary fault structures. Since 2003, we conducted several GPS surveys along the CSAF. The dense GPS measurements, along with data from permanent GPS stations in the area, allow us to constrain the regional strain distribution and contributions from adjacent faults. InSAR is well suited to monitoring details of the shallow slip along the CSAF. However low interferometric correlation and atmospheric signal make it difficult to measure the surface deformation. To resolve aseismic slip at the spatial and temporal resolution we seek integrated use of GPS, InSAR, surface creep, and strain data. EDM and GPS data GPS data NA fixed Deformation adjacent to the CSAF (Agnew, 2004) => GPS results are very coherent with previous EDM measurements. A constant rate fits the data over a 40 year span. 5 surveys => Very little strain on the crustal blocks adjacent to the fault (less than 2 mm/yr of contraction). Kinematics of aseismic slip along the CSAF Distributed slip inversion along the CSAF Burford & Harsh (1980) Lisowski & Prescott (1981) => Geodetic data indicates a slip rate of 32 mm/yr and shallower creep of 29 mm/yr for the CSAF Deformation in the southern part of the CSAFrelated to the Parkfield earthquake Mw6.0, 9/28/2004 Aseismic slip is highly time variable and responds to subtle regional stress changes. Transient slip variations in response to regional deformation events? InSAR data ERS-1 & 2 satellites Track 27, Frame 2871 => No extra slip at time of the earthquake but slip rate increase at end of Oct. 2004, consistent with InSAR analysis. Swath profile at azimuth 47o from difference of the 2 interferograms. Both ENVISAT interferograms show offset on creeping section NW of creepmeter XSC1. (Rosen et al., 1998) km => The stacked interferogram shows a sharp discontinuity in the phase coinciding with the mapped trace of the fault. 10 mm/yr in LOS is about 32 mm/yr of right lateral motion. => East component offset across SAF in creeping section is about 20mm, or about 28mm parallel to fault.