Temporal Slip Rate Response of the Hayward Fault to Static Stress Perturbations Using a Rate and State Constitutive Law

Authors: Schmidt, D. A., Bürgmann, R.

Through recent Coulomb Failure analysis studies, it has become apparent that fault networks form a tightly coupled system where individual faults interact by perturbing the stress field. An example of this interaction was observed along the Hayward fault in response to the static stress perturbation imposed by the 1989 Loma Prieta earthquake. Creep measurements along the southern segment of the fault indicate that reduced slip rates persisted for 4-6 years after the Loma Prieta event (Lienkaemper et al., Science, 1997). In addition, recent GPS and Interferometric Synthetic Aperture Radar (InSAR) data collected since 1992 support earlier observations showing a locked southernmost segment whose return to pre-Loma Prieta slip rate values was signaled by a 2 cm creep event in 1996. Initial analysis of these data also suggest that the eastern face of the fault near Fremont has moved vertically upward relative to the western block at an apparent rate of 3 mm/yr contrary to the long term vertical slip rate of < 0.5 mm/yr. To better understand this slip response we utilize a rate and state constitutive law to solve for the temporal slip rate on a creeping fault in response to a static stress perturbation. A steady state condition is imposed during the derivation to simulate a fault which exhibits stable sliding during the interseismic period. Utilizing the aseismic creep data on the Hayward Fault in response of the Loma Prieta event, we solve for {a}, the weighting of velocity dependence, and {b}, the weighting for time dependent healing, that characterize the top creeping section of the Hayward fault. By assuming that these fit parameters remain constant for a given system, the evolutionary change in slip rate as a function of time and position can be directly calculated.