Abstract

Recent upward revision of the 1872 Owens Valley earthquake from Mw 7.4–7.5 to 7.7–7.9 implies either additional unrecognized rupture length or anomalously strong ground motions associated with this event. We investigate the first possibility through paleoseismic trenching south of the mapped surface rupture in the Haiwee area, where historical accounts suggest significant surface deformation following the earthquake. Trenching focused on a prominent north‐striking scarp, herein termed the Sage Flat fault, expressed in Pleistocene alluvial fans east of Haiwee Reservoir. Surficial mapping and ground‐based Light Detection and Ranging (lidar) surveying suggest that this fault accommodates east‐down normal motion, and possibly a comparable amount of dextral slip. Trenching and luminescence dating brackets the timing of the most recent surface‐rupturing earthquake between ∼25.7 and 30.1 ka, and provides evidence for an earlier event predating this time. In combination with scarp profiling, these dates also suggest a maximum rate of normal, dip‐slip fault motion up to ∼0.1  mm/yr over this period. Although we discovered no evidence for recent surface rupture on the Sage Flat fault, a series of subvertical fractures and fissures cut across young trench stratigraphy, consistent with secondary deformation associated with seismic shaking. As such, we suggest that possible ground disturbance in the Haiwee area during the 1872 event primarily reflected ground shaking or liquefaction‐related deformation rather than triggered slip. In addition, we infer a structural and kinematic connection between the Owens Valley fault and oblique‐dextral faults north of Lower Cactus Flat in the northwestern Coso Range, rather than a west‐step into northern or western Rose Valley. Consideration of these structures in the total extent of the Owens Valley fault suggests a length of 140 km, of which at least 113 km ruptured during the 1872 event.

Online Material: Procedural details and expanded results from the OSL sample analyses, as well as high‐resolution paleoseismic trench logs.

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