Evaluation of Remote Mapping of Active Fault Traces

Accurate fault maps are an important component in the assessment of hazard from fault displacement. Different mapping techniques, biases and ambiguous geomorphic evidence for faulting can drive even expert mappers to produce different fault maps. Another challenge is that future ruptures may not follow past ruptures, so available evidence in the landscape may not lead to accurate rupture prediction. The ultimate goal of my work is to develop a systematized approach for fault mapping so that resulting maps are more evidence-based and ultimately of higher quality I systematized the active fault mapping process and the documentation of evidence for potential fault rupture. I developed and taught a systematic mapping process based on geomorphic landforms evident in remote sensing datasets to undergraduate students, graduate students, and geologic professionals. My approach uses data acquired before historic ruptures to make and test “pre-rupture” fault traces based on the landscape morphology, geomorphology, and geology. The mappers used the Geomorphic Indicator Ranking system (GIR) to represent the geomorphic evidence for faulting such as scarps, triangular facets, offset features, beheaded drainages, and many more. I evaluated the approach in three ways: (1) To assess the geomorphology that best predicts future rupture, I compared the separation distance between the mapped geomorphologic features and the rupture. Scarps and lineaments performed best. (2) I compared the fault confidence chosen by the mapper versus that computed from GIR elements (i.e., mapped geomorphology) near the fault traces. Accurately characterizing fault confidence requires a balance between the mapper input and the calculated confidence rankings. (3) I conducted listening sessions with 21 participants to understand each participant’s approach to fault mapping to highlight best practices and challenges of geomorphic fault mapping. The terminology and mapping process vary by experience level. My approach works both as a teaching tool to introduce tectonic geomorphology and fault mapping to novice mappers, but also works in an industry setting to establish consistent documentation for fault maps. These higher quality fault maps have implications applications of fault mapping including easier dissemination of information, comparison between different fault maps, and hopefully more accurate fault locations for hazard mitigation.