Preliminary Mapping of Surface Fault Rupture and Ground-Deformation Features of the 2019 M6.4 and M7.1 Ridgecrest Earthquake Sequence from Post-Earthquake Lidar and Orthoimagery Datasets

Carla Rosa, Reva Kakaria, & Timothy Dawson

Published August 16, 2021, SCEC Contribution #11557, 2021 SCEC Annual Meeting Poster #077 (PDF)

We present preliminary mapping of surface ruptures and ground-deformation features associated with the 2019 Ridgecrest Earthquake Sequence. The mapping utilizes high-resolution airborne lidar and orthoimagery acquired post-earthquake by the National Center for Airborne Laser Mapping (Hudnut et al., 2020). The MW 6.4 and MW 7.1 earthquakes produced rupture and ground deformation zones approximately 18 km and 50 km in length, respectively, with widespread deformation occurring off the main fault strands. Our goal is to produce a comprehensive and spatially accurate dataset depicting surface ruptures associated with the Salt Wells Valley and Paxton Ranch Fault Zones. We used seamless lidar-derived hillshades, illuminated at 45- and 315-degrees, and supplemented with a multi-directional hillshade as the base imagery. Mapping on the lidar was done at a consistent (1:500 – 1:1000) scale, the largest scale at which imagery resolution is not degraded. Use of this large scale increases our confidence that we have only mapped features that are related to ground deformation from the earthquake. Features on the orthoimagery were mapped at a larger scale (~1:300), allowing for finer-scale features to be resolved. The surface rupture was mapped to highlight the width of deformation zones and to characterize the rupture’s expression through varying terrain, such as pre-existing fault scarps, hillslopes, fan surfaces, and relatively flat playa surfaces. Our mapping reliably resolved ruptures with tens of centimeters and more of relative vertical displacement. Areas with known surface rupture but little vertical displacement are less well-resolved on the lidar compared to the orthoimagery. Mapping using orthoimagery is limited by image resolution, variable image quality, and time available to map at a high level of detail. Thus, characterizing zones of deformation for the 2019 Ridgecrest Earthquake Sequence, important for the assessment of fault displacement hazard, appears to require a paired approach using both lidar and high-resolution aerial imagery. Although these datasets do not capture the same level of detail as low-altitude UAV imagery, our mapping is spatially more complete, improves upon previous mapping of areas with inferred surface rupture, and includes ruptures not previously identified in the field or by preliminary remote sensing.

Citation
Rosa, C., Kakaria, R., & Dawson, T. (2021, 08). Preliminary Mapping of Surface Fault Rupture and Ground-Deformation Features of the 2019 M6.4 and M7.1 Ridgecrest Earthquake Sequence from Post-Earthquake Lidar and Orthoimagery Datasets. Poster Presentation at 2021 SCEC Annual Meeting.

Related Projects & Working Groups
Earthquake Geology