SCEC Award Number 21158 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Beyond the damage zone: Characterizing widespread inelastic deformation from surficial fractures and aftershocks of the Ridgecrest sequence
Investigator(s)
Name Organization
Michael Oskin University of California, Davis
Other Participants Alba Mar Rodríguez Padilla, Elaine Young, Chris Milliner, John Shaw, Andreas Plesch
SCEC Priorities 2a, 3d, 3e SCEC Groups FARM, Geology, Seismology
Report Due Date 03/15/2022 Date Report Submitted 05/18/2022
Project Abstract
 We use post-earthquake lidar data to remotely map surface ruptures produced by the 2019 Ridgecrest Earthquake sequence. Intensively ruptured zones span up to four kilometers in width for both events, with numerous surficial fractures occurring more than 10 km from the main rupture. The first phase of this project was remote mapping of the surface rupture by three independent mappers with various backgrounds in active tectonics. This mapping was done from the post-earthquake airborne lidar (Hudnut et al., 2020), without input from post-earthquake field mapping. Visual comparison of the three remote rupture maps show good agreement for scarps accommodating vertical displacements exceeding 50 cm. For features with smaller vertical displacements, interpretations of the data vary more widely between mappers. The second phase was quantitatively comparing the mapping. To do this, we compare the number of overlapping pixels between rasterized versions of each mappers’ line work with different buffer widths. We find a range of 18 to 54% consistency between remote maps with 1m buffers. The percent overlap increases with buffer width and is higher in areas where the surface rupture was simpler with more vertical offset than areas with complex rupture patterns and/or little vertical offset. In general, field observations and aerial imagery detect more surface rupture features than airborne lidar. Lidar excels for detection and measurement of vertical offsets in the landscape, and it is deficient for detecting lateral offset with little or no vertical motion.
Intellectual Merit Earthquake surface-rupture mapping provides essential data for seismic hazard evaluation
and for understanding earthquake physics. Surface processes result in rapid smoothing and erasure of distributed deformation and fault scarps, requiring rapid field response to capture perishable data. As a result, few parts of a rupture are visited by more than one field team, leading to variable mapping detail and little to no information on the reproducibility of measured offsets. For the Ridgecrest Earthquake Sequence, we use post-earthquake lidar and imagery surveys to interpret and map the surface rupture. We compare results from multiple skilled mappers, and with independently collected field measurements, to objectively analyze the reproducibility of post-event maps.
Broader Impacts This work will provide essential data for probabilistic fault displacement hazard assessments (PFDHA). This project provided summer research support and salary to UC Davis graduate students Alba M Rodriguez Padilla and Elaine K Young; was used as a teaching exercise and a graduate course on active tectonics during which course participants mapped a small part of the rupture using only the lidar data; and facilitated and remote mapping experience to replace field course work for graduating senior Sergio Mendoza during Covid-19 shutdowns. Results from this project were presented at the 2020 and 2021 SCEC annual meetings and results and analysis contributed to three research publication (Rodriguez-Padilla et al., 2021, 2022, Young et al., in prep).
Exemplary Figure Figure 3. Two examples of mapping along the surface rupture. Locations a and b are shown in figure 1. Topographic show the importance of vertical displacement for mapping the surface rupture in the lidar. Gray triangles indicate position of intersections between the mapped surface rupture and the line of section. Line segments above the gray triangles use the same symbology as the map and indicate which mappers have lines at that location. Locations where all three remote mappers consistently mapped the surface rupture correspond to a steep fault scarp in the topographic profiles. The locations were only Ponti et al. (2020) maps the surface rupture are places where there is little vertical change in the topography.