Holocene slip rate of the central Garlock fault in Southeastern Searles Valley, California

Abstract

A Late Pleistocene shoreline at the overflow level of Searles Lake has been displaced 82 to 106 m (preferred value is 90 m) in a left-lateral sense and 2.5 m (net) north side up along the Garlock fault, at the southeastern corner of Searles Valley. Previously published radiocarbon dates from both surface and subsurface strata indicate that the most recent highstand of Searles Lake ended sometime between 10,000 and 13,800 14C years ago. The maximum slip rate of the Garlock fault in southeastern Searles Valley is thus 11 mm/14C yr. If part of the offset of the shoreline occurred during older lakestands, then the slip rate may be somewhat less. A channel incised after the most recent highstand, however, is offset about 68 m, indicating that the minimum slip rate is 5 mm/14C yr. Subjective evaluation of the constraints on the offset and on the age of the shoreline yields a preferred rate of 6–8 mm/14C yr at this site. Assuming Bard et al.'s (1990) recent calibration of the radiocarbon time scale, the calibrated slip rate of the Garlock fault is between 4 and 9 mm/yr with a preferred value of 5–7 mm/yr. This estimate is similar to a previous estimate of the Holocene slip rate and is slightly less than an estimate derived from modelling of geodetic data. Extension north of the Garlock fault in Indian Wells and Searles valleys contributes no more than 3 mm/yr left slip to the Garlock fault.