REINVESTIGATING THE MISSION CREEK FAULT: HOLOCENE SLIP RATES IN THE NORTHERN COACHELLA VALLEY AND IMPLICATIONS FOR SOUTHERN CALIFORNIA EARTHQUAKE HAZARD ASSESSMENT
In support of this goal, detailed fault and quaternary unit mapping was conducted in two field areas along the Mission Creek fault in the northern Coachella Valley. Separated by ~3 km, the two field areas allow for characterization of along-strike changes in Mission Creek fault behavior and interaction with regional faults. Nineteen samples were collected from dextrally offset landforms for Terrestrial Cosmogenic Nuclide (TCN) dating. TCN dating measures the total concentration of in situ produced 10Be, which is proportional to exposure age of the surface. TCN surface dates therefore provide the age constraint for accurate Holocene-Late Quaternary slip rate analysis.
Dated surfaces within Big Morongo Canyon field area yield preliminary TCN ages of 8 ka and 20 ka in locations that record 88-97 m and 31-37 m of dextral displacement, respectively. Based on the calculated dates and measured offsets, local slip rates are calculated to be 11.4-14.0 mm/yr, which is significantly faster than previously estimated rates on the Mission Creek fault in the northern Coachella Valley. Constraining active slip on the Mission Creek fault has significant implications for southern California fault modeling and earthquake hazard assessment, and allows quantification of maximum strain transfer in the Coachella Valley from the Mission Creek fault to the Eastern California Shear Zone (~9 mm/yr).