HR: 0830h
AN: T11D-0424    [PDF]
TI: Effects of Hayward fault interactions with the Rodgers Creek and San Andreas faults
AU: * Parsons, T
EM: tparsons@usgs.gov
AF: USGS, 345 Middlefield Rd, Menlo Park, CA 94025 United States
AU: Geist, E
EM: geist@usgs.gov
AF: USGS, 345 Middlefield Rd, Menlo Park, CA 94025 United States
AU: Jachens, R
EM: jachens@usgs.gov
AF: USGS, 345 Middlefield Rd, Menlo Park, CA 94025 United States
AU: Sliter, R
EM: rsliter@usgs.gov
AF: USGS, 345 Middlefield Rd, Menlo Park, CA 94025 United States
AU: Jaffe, B
EM: bjaffe@usgs.gov
AF: USGS, 345 Middlefield Rd, Menlo Park, CA 94025 United States
AB: Finite-element and crustal-structure models of the Hayward fault emphasize its position within a network of interacting faults, and indicate a number of expected influences from other faults. For example, a new structural cross section across San Pablo Bay in association with potential field maps allows us to map and model detailed interactions between the Hayward and Rodgers Creek faults. The two faults do not appear to connect at depth, and finite-element models indicate growing extensional stress in the stepover between the two faults. A model consequence of extensional stress in the stepover, combined with long-term interaction with the San Andreas fault, is normal-stress reduction (unclamping) of the north Hayward fault. If this occurs in the real Earth, then substantial reduction in frictional resistance on the north Hayward fault is expected, which might in turn be expected to influence the distribution of creep. Interaction effects on a shorter time scale are also evident. The 1906 San Francisco, and 1989 Loma Prieta earthquakes are calculated to have reduced stress on the Hayward fault at seismogenic depths. Models of the 1906 earthquake show complex interactions; coseismic static stress changes drop stress on the north Hayward fault while upper mantle viscoelastic relaxation slightly raises the stressing rate. Stress recovery is calculated to have occurred by ~1980, though earthquake probability is still affected by the delay induced by stress reduction. We conclude that the model Hayward fault is strongly influenced by its neighbors, and it is worth considering these effects when studying and attempting to understand the real fault.
DE: 7221 Paleoseismology
DE: 7230 Seismicity and seismotectonics
DE: 8123 Dynamics, seismotectonics
DE: 8159 Rheology--crust and lithosphere
DE: 8164 Stresses--crust and lithosphere
SC: Tectonophysics [T]
MN: 2003 Fall Meeting