Cordilleran Section - 115th Annual Meeting - 2019

Paper No. 7-5
Presentation Time: 9:00 AM-6:00 PM


LEE, Jeff, Department of Geological Sciences, Central Washington University, 400 East University Way, Ellensburg, WA 98926, DELANO, Kevin M., Instream Flow Unit, Division of Water Rights, State Water Resources Control Board, Sacramento, CA 95814, ROPER, Rachelle, Pioneer Natural Resources, 5205 N. O’Conner Blvd #200, Irving, TX 75039 and CALVERT, Andrew T., US Geological Survey, 345 Middlefield Rd, MS-937, Menlo Park, CA 94025

Strike-slip faults commonly include extensional and contractional bends and stepovers, whereas rotational stepovers are less common. The Volcanic Tableland, Black Mountain, and River Spring areas (CA-NV) (VBR), straddle the transition from the dominantly NW-striking dextral faults that define the northwestern part of the ECSZ into a rotational stepover characterized by dominantly NE-striking sinistral faults that define the southwestern Mina deflection. New field based studies across the VBR allow us to calculate Pliocene to Pleistocene fault slip rates and test predictions for the kinematics of fault slip transfer into this rotational stepover. The VBR is dominated by ~22.9 to 11.4 Ma, ~3.6 to 3.0 Ma, and Quaternary volcanic and sedimentary rocks. These rocks are cut by NS- to NW-striking normal faults across the Volcanic Tableland that transition northward into NS-striking normal faults across Black Mountain and that, in turn, transition northward into NW-striking dextral and NE-striking sinistral faults in River Spring. Measured offset across these faults yield minimum ~EW-extension rates of ~0.5 mm/yr across the Volcanic Tableland and Black Mountain regions, and NW-dextral slip and NE-sinistral slip rates of 0.8-0.9 mm/yr and 0.7-0.9 mm/yr, respectively, across the River Spring region. Two irrotational kinematic fault slip models across the VBR transfer all or a portion of dextral Owens Valley fault slip northwestward into the Mina deflection. In model 1, Owens Valley fault slip is partitioned into two components, one northeastward onto the White Mountain fault zone and one northwestward into the Volcanic Tableland. Slip from the two zones is then transferred northward into the southwestern Mina deflection. In model 2, Owens Valley fault slip is partitioned into three components, with the third component partitioned west-northwest onto the Sierra Nevada frontal fault zone. Applying a simple clockwise rotational model yields predicted sinistral slip rates across the southwestern Mina deflection that are ≥115% greater than our observed minimum slip rates, implying our minimum rates underestimate true sinistral slip rates. Modeled GPS data (Bormann et al., 2016) yields sinistral slip rates that are ≥140% of our measured sinistral slip rates, but similar to the predicted rates in the rotational model.