Refined Holocene Slip Rate for the Western and Central Segments of the Garlock Fault: Record of Alternating Millennial-Scale Periods of Fast and Slow Fault Slip

Abstract

We use lidar- and field-based mapping coupled with single-grain infrared-stimulated luminescence dating to constrain three new slip rate estimates from the western and central segments of the Garlock fault in southern California, revealing a more complete picture of incremental slip rate in time and space for this major plate-boundary fault. These new rates reinforce and refine previous evidence showing that the Garlock fault experiences significant temporal variations in slip rates that span multiple earthquake cycles, with multi-millennial periods of very fast (13-14 mm/yr) early and late Holocene slip separated by a mid-Holocene period of slow slip (3 mm/yr). Similar ca. 8 ka slip rates for the central Garlock fault of 8.8 ± 1.0 mm/yr and 8.2 +1.0/-0.8 mm/yr for the western Garlock fault demonstrate that the fault has slipped at a faster long-term average rate than suggested by previous studies. These fast rates are consistent with kinematic models in which the western and central Garlock fault segments are driven primarily by lateral extrusion associated with N-S contractional shortening, with additional slip driven by WNW-ENE Basin and Range extension north of the fault and minor rotation of the Garlock within the N-S zone of dextral ECSZ shear.