Group B, Poster #108, Earthquake Geology

Evidence for late Holocene multi-fault rupture in the Panamint Valley transtensional relay, Eastern California Shear Zone (ECSZ)

Aubrey LaPlante, Christine Regalla, & Israporn Sethanant
Poster Image: 

Poster Presentation

2022 SCEC Annual Meeting, Poster #108, SCEC Contribution #12484 VIEW PDF
Several historic earthquakes in the Eastern California Shear Zone (ECSZ) have involved complex and multi-fault ruptures, but the fault geometries and background stress conditions that allow for strain transfer across multi-fault systems are still poorly defined. Here we document paleoseismic evidence for complex rupture in Panamint Valley, in the 10 km-wide transtensional relay zone between the NW-striking, dextral oblique-slip Ash Hill and Panamint Valley faults, in order to understand the timing, kinematics and extent of past ruptures, and their relationship to pre-existing faults in the Panamint Valley. We completed 1:4k scale tectonogeomorphic mapping in this 40 km² transtensional relay using National Center for Airborne Laser Mapping (NCALM) lidar DEMs, aerial imagery, and developed a fan chronology consisting of ten generations of late Pleistocene to Holocene alluvial deposits, based on changes in bar and swale morphology, weathering, and desert pavement development. We further date offset deposits using post-infrared feldspar infrared-stimulated luminescence and quantify rupture kinematics offsets at over 250 piercing points in alluvial surfaces using newly generated high resolution (5 cm) drone-based structure from motion digital surface models.
Our high resolution fan mapping and geochronologic dating show three key results: 1) faulting in the transtensional relay is distributed over 100+ fault strands located between the Ash Hill and Panamint Valley faults, occurring in parallel and en echelon arrays, 5-7 km in length, with fault spacings up to 100s of meters; 2) the relay zone has accommodated four earthquakes over the past ~4 ka, and the timing of these events overlap with ruptures on the adjacent Ash Hill and Panamint Valley faults; 3) displacement magnitude per event ranges from 0.6 – 1.0 m of right lateral slip and 0 – 0.2 m of dip slip, with slip kinematics similar to that of the Ash Hill fault. These results suggest that strain is transferred between the Ash Hill and Panamint faults over multiple earthquake cycles via the complex faulting in the transtensional relay, and that strain transfer may be accommodated by slip along an inherited low angle normal fault underlying Panamint Valley. Moreover, our methods and analyses demonstrate how paleorupture extent in fault transition zones may be characterized to determine where multi-fault ruptures may impact seismic hazard estimates.