Complex Holocene Fault Ruptures on the Warm Springs Valley Fault in the Northern Walker Lane, Nevada–Northern California

Abstract

ABSTRACT The Warm Spring Valley fault is a right-lateral strike-slip fault situated in the northern Walker Lane—a region of distributed deformation that accommodates ~15% of the dextral shear between the North American and the Pacific plates. We assess the Holocene slip history through new mapping for the entire fault and a paleoseismic trenching investigation for the northern section of the fault. The fault is expressed in Holocene deposits for a minimum of 80 km and upward of 96 km, encompassing a wide deformation zone (~0.5–2 km) characterized by short discontinuous fault scarps in young alluvial deposits, stepping and anastomosing fault strands, pop-up features, linear drainages, and sag ponds. Trenching on the northern section of the fault reveals evidence for at least two and possibly three surface-rupturing events since 15.8 ± 1.3 ka, matching the timing of the Seehoo highstand of Lake Lahontan. Earthquakes are broadly constrained between 16.4 and 9.2 ka, a possible event between 9.0 and 6.4 ka, and an event between 3.5 and 0.1 ka, determined based on stratigraphic relationships and radiocarbon and optically stimulated luminescence geochronology. The ages of all three earthquakes provide a recurrence interval of ~5.5 ± 1.6 ka for the fault. The earthquake timing overlaps with trenching results from the southern section of the fault, suggesting that full-length fault ruptures generating Mw 7.3–7.4 earthquakes are possible. Post-Lake Lahontan sand dunes are faulted in the Honey Lake basin along with pluvial lake deposits next to Honey Lake, providing supportive evidence for one or multiple Holocene earthquakes. Faults range in orientation from 270° to 360° and match the orientations of shears in clay model experiments suggesting that fault ruptures on the Warm Springs Valley fault are complex, similar to complex historical earthquakes, and consistent with youthful fault development in the northern Walker Lane.