Refining the Southern Extent of the 1872 Owens Valley Earthquake Rupture through Paleoseismic Investigations in the Haiwee Area, Southeastern California

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 anoma- louslystronggroundmotionsassociatedwiththisevent.Weinvestigatethefirstpossibility through paleoseismic trenching south of the mapped surface rupture in the Haiwee area, where historical accounts suggest significant surface deformation following the earth- quake. Trenching focused on a prominent north-striking scarp, herein termed the Sage Flat fault, expressed in Pleistocene alluvial fans east of Haiwee Reservoir. Surficial map- ping and ground-based Light Detection and Ranging (lidar) surveying suggest that this faultaccommodateseast-downnormalmotion,andpossiblyacomparableamountofdex- tralslip.Trenchingandluminescencedatingbracketsthetimingofthemostrecentsurface- 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 am aximum 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, consis- tentwithsecondarydeformationassociatedwithseismicshaking.Assuch,wesuggestthat 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 thanawest-stepintonorthernorwesternRoseValley.Considerationofthesestructuresin 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.