Abstract: Holocene Earthquakes on the Southern Sargent Fault
, San Benito County, California
Erik N. Zinn, Jeffrey M. Nolan, Gerald E. Weber
The Sargent fault
extends for 45 kilometers across San Benito and Santa Clara Counties, California. At its northern terminus, the
fault
appears to merge with the San Andreas
fault
near Lake Ellsman north of Loma Prieta mountain. The
fault
may connect with the Calaveras
fault
south of Hollister, California at its southern terminus. The Sargent
fault
appears to provide the primary control of the geomorphic development of Lomerias Muertas and the Flint Hills northwest of Hollister. Previous estimates of
fault
movement inferred from geomorphic expression are right-lateral reverse-oblique with the southwest side up.
Two trenches were excavated across the fault
in Holocene sediments underlying the flood plain of the Pajaro River, north of Lomerias Muertas. The exposed
fault
dips 70 degrees to the northeast, contrary to previous characterizations of the
fault
, and displays down to the northeast, normal separation, although slickensides on the
fault
surface indicate a primarily horizontal slip vector. At least two Holocene rupture events are suggested by offsets of the stratigraphic section. Dating of C14 samples presently in progress is expected to yield a Holocene slip rate for the
fault
. Funding for this project was provided by USGS National Earthquake Hazards Reduction Program award #1434-94-G2466.
AAPG Search and Discovery Article #90958©1995 AAPG Pacific Section Meeting, San Francisco, California