Comparison of Near-Fault Displacement Interpretations from Field and Aerial Data for the M 6.4 and M 7.1 Ridgecrest Earthquake Sequence Ruptures

Surface fault displacement presents a serious potential hazard for structures an infrastructure lifelines. Roads, shallowly buried pipelines and electrical transmission lines, due to their distributed nature, tend to cover large distances and are bound to go through several fault crossings, especially in active tectonic regions like California. The fault displacement causes strains that can cause important damage and even complete interruption of the system for long periods of time. This constitutes an important source of seismic hazard, yet fault displacement measurements for engineering applications are quite sparse, making the development of predictive models extremely difficult and fraught with large uncertainties. Detailed fault geological mapping exists for a few documented cases, but they may not capture the full width of deformations that are likely to impact distributed infrastructure. The 2019 Ridgecrest Earthquake Sequence presented an ideal case to collect data and evaluate the ability of different techniques to capture coseismic deformations on and near the fault ruptures. Both the M 6.4 and M 7.1 events ruptured the surface in sparsely populated areas and in the desert where little vegetation was present to obscure the surface features. We selected two relatively small study areas (~400 m x 500 m) around the two fault rupture traces for this purpose. We deployed teams and coordinated with data collection campaigns to gather field measurements and photographs as well as imagery from small uninhabited aerial systems and from airborne light detection and ranging.. Each of these techniques requires a different level of resources in terms of labor and time associated with the data collection, processing and interpretation efforts as well as deployment cost. In this paper, we present our methodology along with qualitive and quantitative assessments of the methods used in our two study areas. Our validation showed that 44 overall, the three techniques could capture the features that are important for displacement design of distributed infrastructure. We found that the use of remote sensing methods in combination with some field measurements for calibration presented a strong advantage over the use of a single technique, but that consideration must be made for the resolution of each approach.