ACTIVE DISPLACEMENT TRANSFER BETWEEN THE HUNTER MOUNTAIN – SALINE VALLEY FAULT SYSTEM AND THE FURNACE CREEK – FISH LAKE VALLEY FAULT SYSTEM VIA THE EUREKA VALLEY PULL-APART BASIN, EASTERN CALIFORNIA

The northern Eastern California Shear Zone is bounded on the east by the northwest-trending Furnace Creek – Fish Lake Valley (FC-FLV) fault system that has accommodated ~23-28 km of right-lateral motion since ~4 Ma. The FC-FLV fault system is distorted by an 8-10 km left-step formed by the Cucomungo Canyon Restraining Bend, a marked 1.2 km topographic high flanked to the west by the north-northwest trending Eureka Valley. The Hunter Mountain – Saline Valley (HM-SV) fault system lies ~45 km to the southwest of the FC-FLV fault system and accommodated ~10 km of right-lateral displacement since 4 Ma. The HM-SV and FC-FLV fault systems are linked by north-northeast trending structures that pass displacement through Eureka Valley. On the west, Eureka Valley is bounded by north-northeast striking faults and to the east by north-south to north-northwest trending faults. To assess the subsurface geometry of Eureka Valley, we collected 529 gravity stations at a spacing of 300m along several transects using two Scintrex CG-5 gravimeters with Leica GNSS receivers providing positioning of 2.5 cm or better. The gravity data were merged with 40 existing measurements and, using a reference density of 2.67 g/cm³, reduced to a complete Bouguer anomaly. A residual complete Bouguer anomaly was computed and inverted for depth in three dimensions using Geosoft Oasis Montaj GYM-SYS 3D software. Eureka Valley is underlain by two gravity lows of -18 mGal in the north separated from a -14 mGal low in the south by a northeast trending high of –7 mGal; with corresponding basin depths of ~1.7, 1.1, and 0.6 km, respectively. The northern basin deep coincides with major fault trends and reflects a transition from northeast to north-northwest strike as the northern segment of the FC-FLV fault is approached from the west. The southern sub-basin marks the same change in trajectory but is not directly linked to the FC-FLV fault system and is connected through a 10 km wide belt of north-northeast faults. Estimated minimum vertical displacements of ~2.6 km and ~2.2 km were determined by restoring basement depths to a pre-extensional datum. Using the regional extension direction of N65W and a fault dip of 60°, we calculated an aggregate horizontal extension of ~2.85 km across Eureka Valley. With extension starting after 4 Ma, the average displacement rate is 0.7 mm/yr.