Description
Slip per event and earthquake recurrence interval data for the Agua Blanca fault has previously been estimated based only on empirical evidence. Direct field evidence of lateral offsets and detailed geomorphology has not been examined along the entire fault length. This study mapped previously unmapped geomorphology of the western section of the Agua Blanca fault in Valle Santo Tomas. Evidence of active faulting along the valley is presented here. A 2.4 m fresh offset channel along the ~35km western section appears to be a result of only the most recent surface rupture, suggesting a slip per event of 2.4 m. Combined with the known 4-6mm/yr slip rate, this estimate of slip suggests an earthquake interval of 400-600 years. A 35 km surface rupture length is inconsistent with 2.4 meters of displacement in a single event, casting doubt on the previously published surface rupture behavior of the fault. According to field observations and calculations using the regression of Wells and Coppersmith, the Agua Blanca fault may rupture as much as 85 km of its length, producing earthquakes in the range of M7 .1 - 7.4. With an earthquake interval of possibly 400 years and an estimated time lapse of 350 years since its last surface rupture, the Agua Blanca fault may be accumulating sufficient strain for a destructive earthquake.
