SCEC Award Number 20155 View PDF
Proposal Category Individual Proposal (Data Gathering and Products)
Proposal Title Remote Mapping of Surface Ruptures of the 2019 Ridgecrest Earthquakes
Name Organization
Michael Oskin University of California, Davis
Other Participants UC Davis Ph.D students: Elaine Young, Alba Mar Rodriguez-Padilla, Daniel Kramer
SCEC Priorities 1d, 3a, 3e SCEC Groups Geology, FARM, EFP
Report Due Date 03/15/2021 Date Report Submitted 08/17/2021
Project Abstract
We used post-earthquake lidar data and other imagery to remotely map surface ruptures and measure offsets produced by the 2019 Ridgecrest Earthquake sequence, independent of observations collected in the field. The 4 July MW 6.4 and 5 July MW 7.1 earthquakes produced surface rupture zones approximately 20 km and 50 km in length, respectively, that span up to four kilometers in width, with numerous surficial fractures occurring more than 10 km from the main rupture. The purpose of this study is to develop an objective, uniform map product from which we test 1) the reproducibility of remote surface-rupture mapping and slip measurements between individual remote mappers and 2) the accuracy of remote compared to field-derived surface-rupture mapping and slip measurements. The first phase of this project is remote mapping of the surface rupture by three independent mappers with various backgrounds in active tectonics. This mapping is done from the post-earthquake airborne lidar and imagery data, without input from post-earthquake field mapping. Visual comparison of the three remote rupture maps show good agreement for scarps > 50 cm. For features with less topographic expression, interpretations of the data vary more widely between mappers. Quantitative comparisons range from 40 to 80% consistency between maps. In general, field observations and airborne imagery detect more surface rupture features than airborne lidar. Lidar excels for detection and measurement of vertical offsets in the landscape.
Intellectual Merit Earthquake surface-rupture mapping provides essential data for seismic hazard evaluation and for understanding earthquake physics. Detailed geomorphic features of surface ruptures decay rapidly, 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 two graduating seniors (Sergio Mendoza and Kimberly Bowman) during Covid-19 shutdowns. Preliminary results from this project were presented at the 2020 SCEC annual meeting and final results in analyses will be distributed in one research publication.
Exemplary Figure Figure 1. Comparison of rasterized rupture maps. Mapper 1 lines converted to one meter pixels and compared against mapper 3 lines converted to 1 meter pixels with a 1 m buffer zone. Most of mapper 1 lines lie within the buffered region (green pixels); a few lines fall slightly outside of these buffered zones (blue pixels).