Late Quaternary slip-rate gradient defined using high-resolution topography and 10Be dating of offset landforms on the southern San Jacinto Fault, California

Kimberly D. Blisniuk, Thomas K. Rockwell, Lewis A. Owen, Michael E. Oskin, Caitlin K. Lippincott, Marc Caffee, & Jason Dortch

Published August 3, 2010, SCEC Contribution #1295

The right-lateral San Andreas and San Jacinto faults are the two principal structures accommodating Pacific-North America plate motion in southern California. Recent geologic studies across the plate boundary in southern California suggest that the San Jacinto fault may be the dominant plate boundary structure accommodating this motion. However, because the late Quaternary slip history of this fault system is insufficiently understood, it is difficult to test the partitioning of deformation across the plate boundary and its evolution. Landforms displaced by the Clark fault strand of the southern San Jacinto fault zone were mapped using aerial photography and high-resolution airborne laser-swath topography. Selected features were dated using in situ terrestrial cosmogenic 10Be. Beheaded channels at Rockhouse Canyon, displaced by 500 ± 70 m and 220 ± 70 m, have been dated to 47 ± 8 ka and 28 ± 9 ka, respectively. Farther south, adjacent to the southern Santa Rosa Mountains, an alluvial deposit displaced by 51 ± 5 m has been dated to 35 ± 7 ka. From these sites, the slip rate of the Clark fault strand is determined to diminish southward from 8.8 ± 2.0 to 1.5 ± 0.4 mm/yr. These rates are lower than those for the northern and central stretches of the entire San Jacinto fault zone, and imply a slip-rate decrease along the Clark fault strand from Anza southeastward to its surface termination near the Salton Sea, where slip is transferred to the Coyote Creek fault strand, as well as folding and thrusting in the basin. These data suggest that since ~ 30 to 50 ka, the slip rate along the southern San Jacinto fault zone has been lower than the rate along the southernmost San Andreas fault. This implies that either the slip rate of the San Jacinto fault has substantially decreased since fault initiation, or that fault slip began earlier than some geologic studies suggest.

Key Words
San Andreas fault system, cosmogenic nuclides, slip rates

Citation
Blisniuk, K. D., Rockwell, T. K., Owen, L. A., Oskin, M. E., Lippincott, C. K., Caffee, M., & Dortch, J. (2010). Late Quaternary slip-rate gradient defined using high-resolution topography and 10Be dating of offset landforms on the southern San Jacinto Fault, California. Journal of Geophysical Research, 115(B8). doi: 10.1029/2009JB006346.