DETERMINING SLIP RATES FOR THE WINTER RIM FAULT SYSTEM IN THE SUMMER LAKE BASIN, OREGON
In order to better constrain the slip rate along the WRF, we (1) mapped and analyzed fault scarps and paleoshorelines, and (2) dated paleoshoreline tufas and measured displacements. Topographic profiles across fault scarps along the length of the WRF were analyzed for surface offset. Seventeen carbonaceous shoreline tufa samples spanning elevations from 1,316 m to 1,406 m were collected in the field August 2015, and 21 samples were dated using radiocarbon geochronology (including some duplicates). Ages of the samples range from 12.85 ± 0.12 ka to 40.97 ± 0.48 ka.
A 14.7 ± 0.34 ka paleoshoreline has been offset by 6 m by the Ana River fault, resulting in a slip rate of 0.41 mm/yr, which compares well with rates derived from paleoseismic trenching. A ca. 13.5 ka paleoshoreline been offset by 65 meters across the Summer Lake fault, producing a slip rate of 0.21mm/yr. Offsets measured along fault scarps range from less than 1 m to 40 m, cutting units with ages ranging from Holocene to Oligocene, producing slip rates that fall within reasonable ranges. These new data allow us to refine the spatial and temporal distribution of slip rates within the Summer Lake Basin.