THE INFLUENCE OF PLUVIAL LAKE CYCLES ON EARTHQUAKE RECURRENCE IN THE NORTHWESTERN BASIN AND RANGE EXTENSIONAL PROVINCE

The Basin and Range extensional province hosted large pluvial lakes during the Pleistocene, which generally reached highstands following the Last Glacial Maximum and then regressed rapidly to modern or near-modern levels. These lakes were large and deep enough to profoundly affect the crust through flexure; they filled basins formed by normal faults, and locally modified pore pressure and groundwater conditions. Compilation of geochronologic constraints on paleoshorelines and paleoseismicity suggests temporal correlations between lake level and earthquake recurrence, with changes in slip rates as lakes regressed. In the northwestern Basin and Range (NWBR), climatic and tectonic conditions differ from the rest of the province: the modern and glacial climate is cooler and wetter, glacial lakes were proportionally larger, and the crustal strain rate is lower. Numerous valleys host Holocene normal fault scarps and evidence for earthquakes >M_w7 in the last 15 ka. We compile detailed lake hydrographs, timing of earthquakes and slip on faults, and other climatic and crustal data from Surprise Valley, Summer Lake, the Fort Rock basin, and other basins in the NWBR. We also present new mapping and topographic analysis of fault scarps that provides relative age constraints on the timing of slip events. Our results confirm temporal correlations, but the limited length of the paleoseismic record prevents definitive causation on the scale of the individual fault or lake basin. Taken together, however, data from all basins suggests that the faults in the NWBR could be acting as a system, with pluvial lake cycles affecting elastic strain accumulation and release through slip along normal faults and diking across the region.