HR: 1340h
AN: T43A-1097    [Abstracts]
TI: Paleoseismic and Holocene slip rate investigations along the San Andreas Fault, at Parkfield, California
AU: * Toke, N A
EM: nathan.toke@asu.edu
AF: School of Earth and Space Exploration, Arizona State University PO Box 1404, Tempe, AZ 85287-1404,
AU: Arrowsmith, J R
EM: ramon.arrowsmith@asu.edu
AF: School of Earth and Space Exploration, Arizona State University PO Box 1404, Tempe, AZ 85287-1404,
AB: Prior to the 2004 Parkfield M6 earthquake, we excavated two paleoseismic trenches across the main San Andreas Fault (SAF) ~1 km south of Parkfield, CA. These excavations showed evidence of deformation from both aseismic creep and ground rupturing earthquakes such as the 2004 event. Despite this effort, it remains unclear if the Parkfield segment of the SAF experiences ground rupture from earthquakes >M6. This is an important question for understanding earthquake hazard in central and southern California, especially considering the central California foreshocks that were felt just prior to the 1857 Fort Tejón M 7.9 earthquake. Additionally, numerous slip budget calculations predict a slip deficit of ~5 m extending into the Parkfield segment and suggest that coseismic slip along the Parkfield segment could propagate further southeast. However, these slip budgets do not include a locally-determined geologic slip rate for the Parkfield segment. It is plausible that the slip rate at Parkfield is lower than along the Carrizo segment to the southeast. A lower slip rate would imply a lower seismic hazard from the SAF and indicate that slip is distributed along adjacent structures at Parkfield. To more thoroughly understand the Parkfield segment of the SAF, the Southwest Fracture Zone (SWFZ; which also ruptured in 2004) must be considered in both paleoseismic and slip rate investigations. One site along the SWFZ, Miller's Vineyard site, is located ~1 km west of Carr Hill along the Ranchita Canyon Rd. Here the SWFZ strikes ~315 degrees (parallel to the SAF) and ruptured in the 2004 earthquake. The Miller's Vineyard site is located along an ephemeral tributary of the Little Cholame Creek that appears to be offset right-laterally. Aerial photography suggests that the SWFZ is delineated by a 30 m wide zone of enhanced vegetation that extends more than 100 m. We expect that excavating this site will reveal deformed Holocene layers of fluvial sand, silt, and channel gravels that may be suitable for geologic slip rate investigation. Using the B4 LiDAR data we have identified two other paleoseismic sites of interest along the SWFZ and six sites along the main SAF. Improving the length of earthquake recurrence data and establishing a Holocene slip rate for Parkfield are essential for studies of the temporal aspects of fault strain release histories, fault mechanics, and for characterization of earthquake hazard for south-central California.
UR: http://activetectonics.la.asu.edu/Parkfield/
DE: 7223 Earthquake interaction, forecasting, and prediction (1217, 1242)
DE: 8111 Continental tectonics: strike-slip and transform
DE: 8118 Dynamics and mechanics of faulting (8004)
DE: 8157 Plate motions: past (3040)
DE: 8158 Plate motions: present and recent (3040)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting