Correlations between earthquake recurrence and paleolake changes in Surprise Valley, CA

Abstract:

Slip rates along faults are necessarily time-averaged, calculated by measuring the offset of a feature of known age. Paleoshorelines of pluvial lakes in the Basin and Range are ideal features to use in slip rate calculations, because they (1) are basin-wide, paleohorizontal features that cross faults; (2) can often be precisely dated; and (3) are easily mapped with high-resolution topographic data.

Surprise Valley in the NW Basin and Range is bounded by the active, 90-km long Surprise Valley fault (SVF); the valley also hosted a Pleistocene pluvial lake. Using lidar-derived elevation models, we mapped and measured surface offset across fault scarps and across-basin vertical offsets of dated paleoshorelines that range in age from ~12-30 ka. Paleoshorelines dated at 19.44 ± 1.46 ka in the northernmost 40 km of the SVF are offset 4.74 m, indicating a slip rate of 0.28 mm/yr (assuming a fault angle of 60°). Offset of 16.48 ± 0.87 ka paleoshorelines along the central, 25 km-long segment is 14.38 m, a slip rate of 1.01 mm/yr; offset of 20.85 ± 1.84 ka paleoshorelines along the southernmost segment is 11.5 m, a slip rate of 0.64 mm/yr. In comparison, previous work measurements of offset and slip rate derived from geologic mapping and trenching estimate a slip rate of 0.6 mm/yr for the entire SVF.

The central segment of the SVF has the largest amount of slip and greatest slip rate; both die out towards the fault tips, as expected, though the pattern is asymmetric, suggesting the central and southern segments are acting independently from the northern segment and may be a barrier to earthquake rupture. Additionally, we note that earthquakes occur in a cluster as the paleolake regressed from its most recent highstand, suggesting that slip rate varies through time. These high-resolution datasets allow us to enhance the spatial and temporal resolution of strain accommodation and the earthquake cycle in the northwestern Basin and Range.