HR: 14:25h
AN: S23C-04 INVITED    [Abstracts]
TI: Asperities on the Hayward fault resolved by PS-InSAR, GPS and boundary element modeling
AU: * Funning, G J
EM: gareth@ucr.edu
AF: University of California, Riverside, Geology Building 900 University Ave, Riverside, CA 92521, United States
AU: Burgmann, R
EM: burgmann@seismo.berkeley.edu
AF: Berkeley Seismological Laboratory, University of California 215 McCone Hall, Berkeley, CA 94720, United States
AU: Ferretti, A
EM: alessandro.ferretti@treuropa.com
AF: Tele-Rilevemento Europa, Via Vittoria Colonna 7, Milan, 20149, Italy
AU: Novali, F
EM: fabrizio.novali@treuropa.com
AF: Tele-Rilevemento Europa, Via Vittoria Colonna 7, Milan, 20149, Italy
AB: The Hayward fault shows mixed behaviors -- the majority of the fault surface creeps interseismically, but it is capable of supporting large earthquakes. One explanation for this is that discrete areas of the fault are locked, and accumulating strain, even as surrounding areas creep around them. These locked areas are likely to rupture as asperities in future 1868-like earthquakes. We use PS-InSAR and GPS measurements of surface deformation velocities to identify the creep-rate distribution of the fault, and therefore the areas that are not creeping. We solve first for a kinematic model of the distribution of slip rate on the fault surface using a 3D mesh of triangular dislocation elements that is defined by precisely relocated microseismicity. Then, guided by that solution, we calculate a range of scenarios of boundary element models to resolve the dimensions of the fault area that is fully locked. Slip on deep dislocations underlying the major faults in the San Francisco Bay Area drives the system. Shallow fault elements are either chosen to be locked (zero displacement) or creeping frictionlessly (zero shear traction). The distribution of locked areas which best explains the surface deformation velocities is our preferred model. We find that the pattern of surface velocities is consistent with a 40-km-long locked asperity at the base of the upper crust, extending from Oakland to Union City. The top of this locked zone is shallowest (~4~km) on the 20 km stretch between Oakland and Hayward. In all, around 20% of the fault surface is locked and accumulating a moment deficit equivalent to a M6.5-6.6 earthquake per century. An open question for seismic hazard estimates concerns the seismic potential of the creeping areas - are they also susceptible to rupture, or would any accumulated moment deficit be released instead as aseismic afterslip?
DE: 1240 Satellite geodesy: results (6929, 7215, 7230, 7240)
DE: 1242 Seismic cycle related deformations (6924, 7209, 7223, 7230)
SC: Seismology [S]
MN: 2007 Fall Meeting