Evidence for late Holocene multi-fault rupture in the Panamint Valley transtensional relay, Eastern California Shear Zone (ECSZ)
LAPLANTE, Aubrey(1), REGALLA, Christine(1), SETHANANT, Israporn(2), MAHAN, Shannon A.(3) and GRAY, Harrison J.(3), (1)Earth and Sustainability, Northern Arizona University, (2)University of Victoria, Victoria, CANADA, (3)U.S. Geological Survey, Geosciences and Environmental Change Science Center, DFC, Denver, CO
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Abstract
We present new, high-resolution tectonogeomorphic surficial mapping of Quaternary alluvium and fault scarps in the central Panamint Valley transtensional relay (PVTR), Eastern California Shear Zone. This 250 km2 map compiles newly mapped alluvial fans, lake deposits, and faults in the ~40 km2 between the Ash Hill and Panamint faults to evaluate how strain may be transferred between two fault systems. We completed field and remote mapping of this area between October 2021 and May 2022, at a resolution of 1:12 k and 1:4 k, using GeoEye imagery base maps and existing NCALM 0.5 m airborne lidar DEMs. As existing lidar is unable to resolve small (0.5 – 1m) fault offsets and fan surface morphology, we additionally collected drone-based photogrammetry and produced 5 cm structure-from-motion (SfM) digital surface models (DSMs) to aid in mapping and fault offset analysis. SfM surveys were collected using a DJI Phantom IV drone with a 12.4-megapixel camera, at a height of 75 - 475 m above the ground surface, over 200 m² swaths. Mapping included the development of a high-resolution fan chronology consisting of ten generations of late Quaternary alluvial deposits, based on changes in bar and swale morphology, weathering, and desert pavement development. We further date mapped deposits using post-infrared feldspar infrared-stimulated luminescence, and quantify kinematics by measuring cumulative displacement in the field and from DSMs. Using our fan chronology, inset and burial relationships, IRSL dated deposits, and relationships to spring and lake deposits in the valley, we correlate Quaternary deposits across three fault systems.
These new map data yield the following results: 1) The PVTR has experienced four earthquakes in the last ~4 ka, with each event rupturing different sub-segments of the PVTR; 2) The timing of these earthquakes overlap with rupture timing on the Ash Hill and Panamint faults and each event is bracketed by morphologically similar alluvial fans; 3) Displacement magnitude per event and slip kinematics in the PVTR are similar to that of the Ash Hill fault, but fault orientations are similar to the Panamint fault. Our mapping thus provides new evidence that this complex fault zone may act as a relay for strain transfer between the Ash Hill and Panamint faults over multiple earthquake cycles.
These new map data yield the following results: 1) The PVTR has experienced four earthquakes in the last ~4 ka, with each event rupturing different sub-segments of the PVTR; 2) The timing of these earthquakes overlap with rupture timing on the Ash Hill and Panamint faults and each event is bracketed by morphologically similar alluvial fans; 3) Displacement magnitude per event and slip kinematics in the PVTR are similar to that of the Ash Hill fault, but fault orientations are similar to the Panamint fault. Our mapping thus provides new evidence that this complex fault zone may act as a relay for strain transfer between the Ash Hill and Panamint faults over multiple earthquake cycles.
Motivation for Study
The Eastern California Shear Zone (ECSZ, Figure 1) is a network of immature, complex fault systems (Goldberg et al., 2020) that has been estimated to accommodate between 20 - 25% of the regional deformation of the Pacific - North America plate boundary (Hearn and Humphreys, 1998; Unruh et al., 2003; Lifton et al., 2013). Notably, several historic Mw >6.0 complex and multi-fault earthquakes have ruptured in the ECSZ and northeast Baja, California within the last ~30 years (Figure 1). For example, the 1992 Landers earthquakes (Mw 6.1 Joshua Tree, Mw 7.3 Landers, Mw 6.2 Big Bear), 1999 Mw 7.1 Hector Mine earthquake, the 2010 Mw 7.2 El Mayor-Cucapah earthquake and the 2019 Ridgecrest earthquake sequence (Mw 6.4 Salt Wells Valley and 7.1 Paxton Ranch) all presented similar patterns of slip, multi-fault rupture, or fault linkage across dilatational jogs (Hauksson et al., 1993; Cramer and Darragh, 1994; Jones and Hough, 1995; Rymer et al., 2002; Fletcher et al., 2014; Gonzales-Ortega et al., 2014; Ross et al., 2019; Goldberg et al., 2020; Li et al., 2020; Yamashita et al., 2022). Additionally, the 2010 El Mayor-Cucapah earthquake and 2019 Ridgecrest earthquake sequence involved surface rupture on previously unmapped faults (Gonzales-Ortega et al., 2014; Ross et al., 2019; Goldberg et al., 2020), exposing knowledge gaps in the southern California fault record. These historic ruptures suggest that complex, multi-fault ruptures are a common rupture style in the ECSZ, however, similar complex ruptures are not well documented in paleoseismic records. Additionally, due to the nature of such ruptures, trenching a single fault does not capture the complexity of rupture and distribution of strain along kinematically related, subparallel fault strands. For these reasons, complete surficial tectonogeomorphic mapping is necessary to resolve paleoseismic histories in areas of complex rupture.