Logs and data from the Starthistle trench across a scarp within the Wallula Fault Zone, southeastern Washington

First posted May 16, 2023 For additional information, contact: Earthquake Science CenterU.S. Geological Survey345 Middlefield Road Mail Stop 977 Menlo Park, CA 94025 The Wallula Fault Zone is composed of a series northwest-trending faults and folds that coincide with prominent magnetic anomaly extends uninterrupted for approximately 120 kilometers within the Cascadia back arc southeastern Washington northeastern Oregon. It part geologic structures associated topographic lineament known as Olympic-Wallowa represents relatively narrow zone active faulting seismicity trend along northern flank Horse Heaven Hills. Prior paleoseismic study at an exposure Finley Quarry indicates multiple Quaternary ruptures, including Holocene liquefaction event, demonstrating this fault poses seismic hazard to Tri-Cities region (Richland, Pasco, Kennewick) in Washington. Recent airborne light detection ranging (lidar) data coverage east Columbia River reveals 0.5-meter-high south-facing scarp extends, almost continuously, about 25 km base As effort assess characterize posed by Zone, we excavated studied trench across understand its origin potential history rupture zone. We present preliminary mapping site information from investigation. These field laboratory may support development latest Pleistocene surface Zone.