HR: 0800h
AN: S21A-0240    [Abstracts]
TI: Linking Faults: Subsurface Creep on a Contiguous Fault Structure Connecting the Hayward and Calaveras Faults
AU: * Evans, E
EM: eileen@seismo.berkeley.edu
AF: Berkeley Seismological Laboratory, 215 McCone Hall, UC Berkeley, Berkeley, CA 94720- 4760, United States
AU: Burgmann, R
EM: burgmann@seismo.berkeley.edu
AF: Berkeley Seismological Laboratory, 215 McCone Hall, UC Berkeley, Berkeley, CA 94720- 4760, United States
AU: Nadeau, R
EM: nadeau@seismo.berkeley.edu
AF: Berkeley Seismological Laboratory, 215 McCone Hall, UC Berkeley, Berkeley, CA 94720- 4760, United States
AB: The Hayward Fault is the most likely Bay Area fault to rupture in a major earthquake in the next 30 years. Much of the Hayward fault experiences 3-6 mm/yr of creep at the surface, approximately half of its estimated long-term slip rate (~9mm/yr). The southernmost section of the Hayward fault, however, appears to be creeping at up to 9 mm/yr, before creep abruptly ceases just south of Freemont, CA. East of Fremont, the Calaveras Fault transitions from about 15 mm/yr of slip along its creeping southern section, to about 6 mm/yr in the north. Based on location and slip, it seems very likely that the Calaveras fault directly transfers the deficit 9 mm/yr of slip as creep to the Hayward Fault. The existence of characteristic repeating earthquakes in this region strongly suggests that active creep indeed occurs between the two faults. Seismic studies of the Hayward-Calaveras stepover have suggested that the southern Hayward fault may in fact dip into and merge with the northern Calaveras Fault south of Fremont, CA. Improved GPS-derived surface velocities and consideration of new PS-InSAR range-change rates in the area help verify and constrain this proposed geometry, and allows a reevaluation of slip on these faults. A dislocation model combining seismically derived geometry and GPS velocities confirms that active fault creep occurs on the continuation of the dipping surface of the Hayward Fault effectively linking the Hayward and Calaveras Faults along a contiguous structure. The revised model provides an estimate of the distribution of creep on the three-dimensional fault surface through the stepover region, thus aiding in evaluating the seismic potential and rupture scenarios in the area.
DE: 1209 Tectonic deformation (6924)
DE: 7212 Earthquake ground motions and engineering seismology
DE: 7221 Paleoseismology (8036)
DE: 7223 Earthquake interaction, forecasting, and prediction (1217, 1242)
DE: 8175 Tectonics and landscape evolution
SC: Seismology [S]
MN: 2007 Fall Meeting