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

May 16, 2023


The Wallula Fault Zone is composed of a series of northwest-trending faults and folds that coincide with a prominent magnetic anomaly that extends uninterrupted for approximately 120 kilometers within the Cascadia back arc of southeastern Washington and northeastern Oregon. It is part of the geologic structures associated with the topographic lineament known as the Olympic-Wallowa lineament and represents a relatively narrow zone of active faulting and seismicity that trend along the northern flank of the Horse Heaven Hills. Prior paleoseismic study of the Wallula Fault at an exposure at Finley Quarry indicates multiple Quaternary ruptures, including a Holocene liquefaction event, demonstrating that this fault zone poses a seismic hazard to the Tri-Cities region (Richland, Pasco, Kennewick) in southeastern Washington.

Recent airborne light detection and ranging (lidar) data coverage east of the Columbia River reveals an approximately 0.5-meter-high south-facing scarp east of the Columbia River that extends, almost continuously, for about 25 km to the east along the base of the Horse Heaven Hills. As part of an effort to assess and characterize the seismic hazard posed by the Wallula Fault Zone, we excavated and studied a trench exposure across the scarp to understand its origin and the potential history of rupture along the fault zone. We present preliminary mapping and trench site information from a paleoseismic investigation. These field and laboratory data may support development of a history of the latest Pleistocene and Holocene surface rupture within the Wallula Fault Zone.

Publication Year 2023
Title Logs and data from the Starthistle trench across a scarp within the Wallula Fault Zone, southeastern Washington
DOI 10.3133/sim3495
Authors Stephen J. Angster, Brian L. Sherrod, John Lasher
Publication Type Report
Publication Subtype USGS Numbered Series
Series Title Scientific Investigations Map
Series Number 3495
Index ID sim3495
Record Source USGS Publications Warehouse
USGS Organization Earthquake Science Center