INTEGRATING SURFICIAL GEOLOGIC MAPPING WITHIN AN EXISTING BEDROCK FRAMEWORK IN THE NORTHERN OLYMPIC PENINSULA, CLALLAM COUNTY, WA

New high-resolution surficial geologic mapping in the Northern Olympic Peninsula of Washington State reveals a complex series of glacial, fluvial, and colluvial landforms, as well as evidence of post-glacial faulting and mass movements. Existing framework mapping in this area at 1:100,000 focuses on bedrock and structures related to deposition and accretion of deformed sedimentary rocks. Publicly available, high-resolution airborne lidar data spanning this area provides new opportunities to evaluate this landscape and the complex glacial and tectonic geomorphology associated with the active, dextral North Olympic fault zone (NOFZ). We used field and lidar analysis to build upon existing bedrock mapping and existing high-resolution surficial mapping adjacent to the study area to produce a new 1:4,000 surficial map. Our mapping reveals 17 surficial units and over 20 km of segmented fault scarps that extend the total strike length of the NOFZ to 89 km. Additionally, we collected and analyzed 7 samples for luminescence dating of post-glacial fluvial terraces, outwash surfaces, and alluvial fan deposits to bracket the timing of surface rupturing earthquakes and to provide constraints on the post-glacial slip rate of the western NOFZ. Our approach highlights several opportunities associated with integrating surficial geological mapping using existing an bedrock framework. In the beginning of the study, strike and dip measurements from bedrock mapping were critical in aiding our distinctions between bedrock planes, glacial striae, and fault scarps. An overlay of our mapped post-glacial fault scarps with the older bedrock structures may indicate that discrete ruptures along the fault may be guided by older bedrock structures. Significant differences in resolution between our surficial mapping and the existing bedrock framework proved to be a challenge when integrating the two sets of data. Despite the resolution differences, combining our high resolution mapping with existing bedrock mapping allowed us to confidently characterize fault scarps and recognize relationships between old and new structures.