PRELIMINARY ASSESSMENT OF SIERRA NEVADA RANGE-FRONT FAULTING IN INDIAN WELLS VALLEY, EASTERN CALIFORNIA

Indian Wells Valley (IWV) is a seismically active graben located in eastern California on the southwestern edge of the Basin and Range province. The valley is crossed by four principal fault zones with late Pleistocene to historical activity that include the north striking normal Sierra Nevada Frontal fault, and the Little Lake fault, Airport Lake fault, and Paxton Ranch fault, all of which strike north to northwest and display oblique right-lateral slip. IWV is one of the most seismically active basins in eastern California with M4.9, 5.8, and 6.4/7.1 earthquakes occurring in 1982, 1995, and 2019, respectively. Despite being seismically active, the vertical and lateral slip rates on the SNFF and other fault zones are poorly characterized.

This study uses 1:5000-scale geomorphic and fault zone maps along with fault scarp measurements to characterize the relative age of offset landforms and magnitude of vertical separation on the SNFF. Quaternary geomorphic and fault maps were produced for the northwestern sector of the valley from the range front eastward to China Lake basin. Five alluvial fan units were identified and assigned relative ages: Qf1 (old), Qf2 (intermediate), Qf3 (intermediate-young), Qf4 (young), and Qf5 (active). A 2-meter digital elevation model and field surveying were used to generate fault scarp profiles across alluvial fan surfaces along 22 km of range front. Vertical separation of fault scarps on Qf1 surfaces range from 8 – 18 m and from 2 – 4 m on Qf2 surfaces. Planned numerical age dating of offset Qf1 and Qf2 deposits will afford the first vertical slip rate estimates on the SNFF in IWV and provide useful information to begin characterizing the vertical slip distribution across all the principal faults in the valley.