PRELIMINARY CONSTRAINTS ON THE QUATERNARY SLIP HISTORIES OF THE EUREKA VALLEY FAULT AND THE DRY MOUNTAIN FAULT WITHIN THE EASTERN CALIFORNIA SHEAR ZONE, DEATH VALLEY REGION

The Eastern California Shear Zone (ECSZ) is a broad, NW-trending corridor of intracontinental right-slip shear that accommodates ~10-13 mm/yr (~15-25%) of the relative North American-Pacific plate motion. The ~300-km-long northern segment of the ECSZ, located between the Garlock fault to the south and the Mina Deflection to the north, is expressed by two zone-bounding right-slip faults and at least five N- to NE-striking normal faults. Many studies have examined the Quaternary slip rates and earthquake histories of the right-slip faults. However, few neotectonic investigations have focused on the normal faults despite their regional prominence and evidence of seismic activity (e.g., 1993 Mw 6.1 Eureka Valley earthquake). In addition, the role of the normal faults in accommodating right-slip shear and transferring slip across the ECSZ remains inadequately understood. Researchers disagree whether the faults enable (1) clockwise rotation of crustal blocks via oblique-slip motion (i.e., rotating bookshelf-fault model) or (2) NW-SE extension via dip-slip motion (i.e., displacement-transfer fault model). In this study, we present the preliminary results of neotectonic mapping, GPS-based surveying, and luminescence geochronology along two of the normal faults, the Eureka Valley fault and the Dry Mountain fault. The Eureka Valley fault is expressed as series of Quaternary alluvial scarps with heights and lengths up to ~15 m and ~2 km, respectively, that were generated during one or more slip events. The fault displays no evidence of recent strike-slip motion. An early estimate of the late Pleistocene-Holocene slip rate along the Eureka Valley fault is ~0.5 mm/yr, which approaches the rates of regional normal faults that have triggered M >6 earthquakes. Furthermore, this preliminary slip rate represents a substantial portion of the regional slip budget and highlights the importance of the normal faults in accommodating right-slip shear. The Dry Mountain fault is expressed in some locations as a discrete fault surface within Paleozoic bedrock strata that dips ~50°-60°W and features down-dip W-plunging (~55°W) striations. The lack of evidence of strike-slip motion along both normal faults and the observation of down-dip striations along the Dry Mountain fault, which has also been observed along the Deep Springs fault and the Tin Mountain fault in the region, suggests that these faults have predominantly dip-slip kinematics. These observations are consistent with the predictions of the displacement-transfer fault model of the ECSZ.