NEW AGE AND GEOMORPHIC CONTROLS ON THE BOULDER FRONT FAULT, WOOD RIVER BASIN, NORTHERN BASIN AND RANGE PROVINCE, IDAHO
We present results from the analysis of a segment of the Boulder front fault along the Boulder Creek scarp sought to determine the age of past ruptures of this segment of the fault. Geologic mapping separated four surficial and glacial deposits along the Boulder Creek lower drainage. The segment of the fault was profiled with differential GPS along 6 transects orthogonal to the scarp. The diffusional degradation of the scarp was modeled and age inferred. Scarp heights are ~1m to ~ 4m and are higher in older deposits, demonstrating repeated ruptures along the segment. Stratigraphically controlled 14C ages of ~2720±30 and 3190±30 y are determined for the lowest terraced deposit, which still present offset. The slip rates on this rupture was ~0.6 m/my. Results of modeling the topographic development of the watershed predicts fault slip may have begun 0.6-1Ma.