SCEC Award Number 22087 View PDF
Proposal Category Individual Proposal (Data Gathering and Products)
Proposal Title Constraining over a Decade of Fault Creep Along the Southern San Andreas Fault from Differential Topography
Investigator(s)
Name Organization
Chelsea Scott Arizona State University
Other Participants Ramon Arrowsmith
Michael Bunds
SCEC Priorities 1a, 3b, 1e SCEC Groups Geodesy, Geology, SAFS
Report Due Date 03/15/2023 Date Report Submitted 04/22/2024
Project Abstract
 Our project focused on resolving shallow fault creep along the Creeping Section of the Southern San Andreas Fault (SSAF) from hybrid lidar- and sUAS-SfM (drone) 3D topographic differencing. We were motivated by the increasing community interest in topographic differencing and sUAS dataset collection for use in seismic hazard research. We also wanted to explore the high quality sUAS topography georeferencing requirements for differencing studies. We conducted 3D differencing with the 2004 B4 and 2010 Salton Sea lidar topography datasets with a 2020 sUAS-SfM dataset that our group collected adjacent to the Salton Sea. Unfortunately, the significant flight line errors in the two lidar datasets hindered our ability to resolve the 1-6 mm/yr fault creep over the decadal timescale. To mitigate the impact of these errors, we internally aligned overlapping lidar flightlines. For the 2004 B4 to 2020 sUAS-SfM differencing, this correction improved the visual appearance of the displacement map, and the resulting fault creep rates were more consistent with published InSAR-derived creep rates. Resolving millimeter per year fault creep rates with topographic differencing is very challenging especially with the use of legacy or older lidar datasets that are likely to have larger errors than modern lidar datasets.
Intellectual Merit This project had four main goals: (1) constrain new decadal-scale creep rates along the SSAF, (2) advance topographic differencing methods to resolve deformation along low creep rate faults, (3) make recommendations for working with the increasingly popular sUAS-SfM datasets, and (4) map the location of the active fault trace over the decadal scale. Despite our best efforts, we were unable to measure new decadal-scale creep rates along the SSAF from topographic differencing, because the errors in the B4 lidar dataset are significant especially relative to the SSAF's low creep rate. We showed that a major limitation in differencing is the quality of the legacy or older lidar datasets that were acquired ~10-20 years ago. This also emphasizes the high quality georeferencing requirements of sUAS-SfM datasets to be used in differencing. These conclusions are important as differencing studies often use legacy datasets as the "pre"-event data and sUAS-SfM as the "pre" or "post" event data.
Broader Impacts The main goal of this work was to test how we can best resolve shallow fault creep along the Creeping Section of the Southern San Andreas Fault (SSAF) from hybrid lidar- and sUAS-SfM (drone) 3D topographic differencing. This approach can be used to measure fault slip rates, which serve as important inputs into seismic hazard assessment. This work showed that resolving millimeter per year fault creep rates with topographic differencing is very challenging especially with the use of legacy or older lidar datasets that are likely to have larger errors than modern lidar datasets. This has important implications for the collection of future datasets to be use for topographic differencing to constrain fault slip rates.
Exemplary Figure Figure 2: 2004 B4 and 2020 sUAS differencing results showing the northwest displacement field. The black line is the San Andreas fault from the USGS Quaternary fault and fold database (USGS, 2022). The “corrected” differencing maps reflect the internally aligned B4 dataset, as described in the text.