Challenges and Strategies for Characterizing Low Strain-Rate Faults

Emerson Lynch

Submitted September 7, 2025, SCEC Contribution #14600, 2025 SCEC Annual Meeting Poster #TBD

Low strain-rate faults (≤1 mm/yr) exist in many tectonic settings, from highly active plate boundaries to stable intraplate regions. Although they comprise a small component of the moment budget, such faults can help us understand how distributed strain is accommodated throughout a region. Additionally, these faults can produce moderate to large (M5-8) earthquakes that pose hazard to nearby communities and infrastructure. Low strain-rate faults are often not well characterized due to limited instrumental (seismic and geodetic) data, cryptic geomorphic expression, and poor preservation. Here, I discuss challenges faced in characterizing low strain-rate faults, including dense vegetation, erosion and deposition that obscure faults or create misleading features, landsliding, and anthropogenic modification. I also discuss the methods we used to address these challenges by highlighting specific examples from previous work. High-resolution (≤m-scale) lidar data is now readily available, aiding geomorphic mapping in vegetated regions like Puerto Rico and Cascadia. In relatively unvegetated areas, extremely high resolution (~cm-scale) drone imagery and derived digital terrain models can capture subtle features, like ~30-cm-high scarps along the oblique Ash Hill fault in the Eastern California Shear Zone. Historical imagery can help reveal past anthropogenic modification, such as decades-old logging roads in British Columbia, or fault scarps that were obscured by recent development in Puerto Rico. Shallow geophysical surveys can aid in characterization of shallow subsurface geometry, as well as test whether geomorphic expression corresponds to faults in the subsurface. Detailed field work remains critical, both for ground-truthing remote observations and for accurately measuring displacements. Where lidar isn’t of sufficient quality to measure displacements, total station surveys can provide precise measurements of landforms and displacements without the unobstructed sky coverage needed for GNSS. I invite further conversation on the challenges faced by other researchers and strategies for characterizing low strain-rate faults in any tectonic setting.

Citation
Lynch, E. (2025, 09). Challenges and Strategies for Characterizing Low Strain-Rate Faults. Poster Presentation at 2025 SCEC Annual Meeting.

Related Projects & Working Groups
Earthquake Geology