Kinematics, asperities and seismic potential of the Hayward fault, California from ERS and RADARSAT PS-InSAR

Gareth Funning(1) , Roland Burgmann(1) , Alessandro Ferretti(2) , Fabrizio Novali(2) , and David Schmidt(3)

(1) University of California, 215 McCone Hall, Berkeley, CA, 94720, United States
(2) Tele-Rilevamento Europa, Via Vittoria Colonna 7, 20149 Milano, Italy
(3) University of Oregon, 1272 University of Oregon, Eugene, OR, 97403, United States


The Hayward fault is currently considered to carry the greatest risk of a destructive (Mw > 7.0) earthquake of all of the strike-slip faults in the San Francisco Bay Area, California. Part of the San Andreas Fault Zone, it is estimated to accommodate some 25% of the total Pacific-N America relative plate motion at this latitude. Published studies using conventional InSAR, creepmeter and GPS data suggest that on average the upper 4-6 km of the fault is creeping at a rate of approximately 5 mm/yr, approximately half of published geologic slip-rate estimates.

InSAR data have already been shown to provide considerable insight into the kinematic behaviour of the Hayward fault (Schmidt et al., 2005, JGR). Three areas have been identified where the local creep rate, estimated on the fault using boundary element elastic modelling, is very low (< 2 mm/yr). Given their location at the base of the fault, these probably represent locked asperities, areas which could be the loci of deformation in any future earthquake. Current studies are limited by the poor interferometric coherence seen east of the fault; since only one side of the fault has adequate data coverage, resolution in models derived from such data is necessarily limited, especially at depths greather than 5 km.

In this study we present the preliminary results of an expanded InSAR study of the Hayward fault. We apply permanent scatterer InSAR (PS-InSAR) techniques to the full archive (1992-2004) of ERS and RADARSAT data covering the Hayward fault in both ascending and descending acquisition geometries. Thereby we create the most complete spatio-temporal picture of the deformation in this area yet assembled. In particular, our data have significantly improved data coverage on the eastern side of the fault. We use this dataset, combined with information from GPS and creepmeters, to generate an improved model of the distribution of slip rate over the fault, utilising the permanent scatterer time series to model in addition, the evolution of the slip rate pattern with time. Results are compared with an expanded stack of ERS interferograms covering the same time interval, produced by conventional means. We also use the improved spatial resolving power of the data to investigate different asperity models -- for instance, to determine the extent of each asperity, and to estimate its likely stress drop and seismic potential. In future, such models may be useful in assessing and quantifying the state of friction on this and similar faults, allowing us to deepen our understanding of the behaviour of faults that are accumulating elastic strain.



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