Evidence of Previous Faulting along the 2019 Ridgecrest, California, Earthquake Ruptures

Abstract

The July 2019 Ridgecrest earthquakes in southeastern California were characterized as surprising by some, because only ∼35% of the rupture occurred on previously mapped faults. Employing more detailed inspection of pre-event high-resolution topography and imagery in combination with field observations, we document evidence of active faulting in the landscape along the entire fault system. Scarps, deflected drainages, and lineaments and contrasts in topography, vegetation, and ground color demonstrate previous slip on a dense network of orthogonal faults, consistent with patterns of ground surface rupture observed in 2019. Not all of these newly mapped fault strands ruptured in 2019. Outcrop-scale field observations additionally reveal tufa lineaments and sheared Quaternary deposits. Neotectonic features are commonly short (<2 km), discontinuous, and display en echelon patterns along both the M 6.4 and M 7.1 ruptures. These features are generally more prominent and better preserved outside the late Pleistocene lake basins. Fault expression may also be related to deformation style: scarps and topographic lineaments are more prevalent in areas where substantial vertical motion occurred in 2019. Where strike-slip displacement dominated in 2019, the faults are mainly expressed by less prominent tonal and vegetation features. Both the northeast- and northwest-trending active-fault systems are subparallel to regional bedrock fabrics that were established as early as ∼150 Ma, and may be reactivating these older structures. Overall, we estimate that 50%–70% (i.e., an additional 15%–35%) of the 2019 surface ruptures could have been recognized as active faults with detailed inspection of pre-earthquake data. Similar detailed mapping of potential neotectonic features could help improve seismic hazard analyses in other regions of eastern California and elsewhere that likely have distributed faulting or incompletely mapped faults. In areas where faults cannot be resolved as single throughgoing structures, we recommend a zone of potential faulting should be used as a hazard model input.

Coseismic Surface Displacement in the 2019 Ridgecrest Earthquakes: Comparison of Field Measurements and Optical Image Correlation Results

“…Thompson Jobe et al. (2020) reported that 50%–70% of the fault strands that ruptured in 2019 correspond to neotectonics features that predate the 2019 event, including subtle scarps, vegetation lineaments, and deflected drainages. However, those investigators were only able to identify a handful of sites with clear markers that record dextral motion along the Paxton Ranch fault.…”

“…WorldView imagery accessed under the NextView license (©DigitalGlobe 2020). Displacement measurements from optical pixel correlation available in Gold et al (2020). Optical pixel correlation results available in Barnhart et al (2020a).…”

Accommodation of Plate Motion in an Incipient Strike‐Slip System: The Central Walker Lane

“…Subsequent studies have shown that many of the respective seismogenic faults have recurrence times on the order of ~3-15 ka, and that, if present, scarps from prior events are heavily degraded (Rubin and Sieh, 1997;Bell et al, 1999;Rockwell, 2000). Many of the faults that accommodated these ruptures are neither major through-going structures nor range-bounding faults (Bell et al, 1999;Jobe et al, 2020;Koehler et al, 2020). We suggest that future M7 strikeslip events in the Central Walker Lane may be similar to these events, and might occur across a series of previously recognized and unrecognized structures.…”

Bookshelf Kinematics and the Effect of Dilatation on Fault Zone Inelastic Deformation: Examples From Optical Image Correlation Measurements of the 2019 Ridgecrest Earthquake Sequence

“…The mainshock rupture terminated at its northern extent within the Coso volcanic field and at its southern extent ∼5 km from the Garlock fault, where it was found to have triggered creep at the surface along parts of the Garlock fault and a small cluster of seismicity (Barnhart et al., 2019; Ross et al., 2019). Field‐ and remote‐based mapping of geomorphic markers and vegetation lineaments indicate that both fault systems involved in the foreshock and mainshock show extensive evidence for faulting before their rupture in 2019 (Jobe et al., 2020), but their geologic fault slip rates currently remain unknown. The Ridgecrest sequence is also notable.…”