Late Pleistocene kinematics of the central San Jacinto fault zone, southern California.

摘要

Geologic mapping, structural analysis and geographical information system (GIS) surface analyses are used to describe the late Pleistocene kinematics along the central San Jacinto fault zone (SJFZ) of southern California, a 300 km long zone of dextral shear in the San Andreas fault system. The Clark and Coyote Creek faults are the two active strands of the central SJFZ. The Fonts Point Sandstone is deposited on an unconformity surface modeled with a GIS to measure late Pleistocene uplift and folding. Borrego Sink Lake deposits chronicle lake levels and deformation along the Coyote Creek fault. The late Pleistocene slip rate of the Clark fault is estimated by restoring slip to the best-fit location using a GIS and digital landscape model. I use these results to produce a late Pleistocene kinematic history and tectonic model for the central SJFZ.; Onset of Fonts Point Sandstone deposition is estimated at 500 ± 40 ka, and is related to the initiation of the Coyote Creek fault at 600 ± 100 ka. The Borrego Sink Lake beds are between 200 and 20 k yrs old and are related to restraining stepovers in the Coyote Creek fault. Much of the deformation in the Borrego Badlands and Borrego Sink area took place after Coyote Creek fault initiation. Deformation across the Borrego Badlands area is related to restraining stepovers from the Imperial fault to the Coyote Creek fault, with intermediate stepovers to the Clark and San Felipe Hills faults. Slip transfer to the Clark fault deformed the San Felipe Hills, and a stepover to the Coyote Creek fault uplifted Fonts Point. The slip rate along the southeastern Clark fault decreased from the long-term rate of 10 ± 2 to 6 ± 2 mm yr−1 since 200–300 ka.; The activation of the Coyote Creek fault may be a simplification of fault-zone geometry that caused a decrease in slip rate along the Clark fault. In the future the Coyote Creek fault could breach the releasing step at its northwest end and, with the northern section of the Clark fault, create a segment that connects the Superstition Hills to Anza in a more optimal orientation within the regional stress field.