HR: 15:10h
AN: T12E-06    [PDF]
TI: Faulting Plumbing: Spring Response to Creep on the Hayward Fault
AU: Manga, M
EM: manga@eps.berkeley.edu
AF: Dept. Earth \& Planetary Science, 307 McCone Hall University of California, Berkeley, CA 94720 United States
AU: Manga, M
EM: manga@eps.berkeley.edu
AF: Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 United States
AU: * Rowland, J C
EM: rowland@eps.berkeley.edu
AF: Dept. Earth \& Planetary Science, 307 McCone Hall University of California, Berkeley, CA 94720 United States
AU: * Rowland, J C
EM: rowland@eps.berkeley.edu
AF: Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 United States
AB: Two prominent sets of thermal springs lie along the western edge of the left step over region between the Calaveras and Hayward faults: the Alum Rock springs, San Jose, CA, and the Warm Springs, Fremont, CA. Co- and postseismic flow increases at both spring locations have been well documented (King et al., 1994 and Waring, 1915). Until recently, however, spring response to creep events was unknown. In January 2003, we documented a 20% decrease in discharge at the Warm Springs due to a 0.31mm right lateral creep event on the southern Hayward fault. The Warm Springs emanate from the Warm Springs fault that lies at the base of Mission Peak and merges with the Mission fault. The observed decrease in discharge is directly proportional to fluid pressure drop within the fault and therefore we suggest that creep on the Hayward fault resulted in a rapid stress change within a neighboring secondary fault. We present an analytical model that explains the observed discharge change and provides an estimate for the depth of fault zone permeability changes. Our results indicate that ongoing monitoring, geochemical sampling, and modeling of thermal springs within active faults zones offers the potential to directly observe fluid-fault interactions and better constrain the interactions of major fault zones with neighboring secondary faults.
DE: 8130 Heat generation and transport
DE: 8135 Hydrothermal systems (8424)
DE: 8158 Plate motions--present and recent (3040)
DE: 8164 Stresses--crust and lithosphere
SC: Tectonophysics [T]
MN: 2003 Fall Meeting