FAULT SCARP MORPHOLOGY ALONG THE EUREKA VALLEY FAULT ZONE, EASTERN CALIFORNIA, U.S.A

Eureka Valley, CA, in northwestern Death Valley National Park, is one of a series of valleys formed by oblique extension within the Eastern California shear zone and Walker Lane belt. In Eureka Valley, extension is accommodated by the normal-oblique, north-south trending Eureka Valley fault zone (EVFZ) that bounds the valley’s east side at the foot of the Last Chance Range and has visible Quaternary fault scarps. A M_w 6.1 earthquake on May 17, 1993 near the west side of Eureka Valley did not produce substantial ground rupture. In Northern Eureka Valley, the EVFZ offsets Quaternary alluvial-fan deposits with an age ~2-12 ka that display subdued bar and swale morphology and light desert varnish. Three scarp profiles were surveyed showing two events. Scarp profile 1 displays a right lateral offset of 3.2 m and a vertical offset of 0.7 m. Scarp profiles 2 and 3 show vertical offsets of 1 m and 1.5 m, respectively, with no horizontal offset. Results indicate minimum slip rates of 0.26 – 1.6 mm/yr over the last 2-12 ka. These results correlate with the geodetic slip rates of 0.2 mm/yr; however, EVFZ slip rates determined on scarps to the south were 0.04 – 0.13 mm/yr whereas the southernmost EVFZ is inactive over the last 30 ka. Based on the parallel trends of the northern scarps and the 1993 event we suggest that the cross-valley fault in Eureka Valley is the more active fault strand. The development of a cross-valley fault is consistent with clay models and field observations of a basin in the late extension phase.