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Group B, Poster #076, Earthquake Geology

Assessing a systematic geomorphic mapping approach to improve confidence in fault mapping and rupture prediction

Rachel N. Adam, Chelsea P. Scott, Ramon Arrowsmith, Darryl Reano, Christopher M. Madugo, Rich D. Koehler, Malinda G. Zuckerman, Brian Gray, Ozgur Kozaci, Tania Gonzalez, Hans AbramsonWard, Thomas K. Rockwell, Eldon M. Gath, Albert R. Kottke, & Ethan Luechter
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Poster Presentation

2023 SCEC Annual Meeting, Poster #076, SCEC Contribution #13222 VIEW PDF
Accurate fault maps are an important component in the assessment of fault displacement hazard. Different mapping techniques, biases, and ambiguous geomorphic evidence for faulting can drive even expert mappers to produce different fault maps. There is wide variation in how fault trace linework and supporting geomorphic, geologic, and morphologic evidence is documented. This variation can lead to difficulty disseminating and comparing fault maps.

In this study, we developed and evaluated a systematized fault mapping approach and documentation of fault evidence based on desktop mapping of remote sensing datasets. Our systematized approach works both as a teaching tool to introdu...
ce tectonic geomorphology and fault mapping to novice mappers, but also works in an industry setting to establish consistent documentation for fault maps. The resulting higher quality fault maps have multiple applications including easier dissemination of information, comparison between different fault maps, and hopefully more accurate fault locations for hazard mitigation.

Our mapping process emphasizes consistent documentation of observations and evidence that lead the mapper to an accurate fault location based on the mapped tectonic geomorphology. Our approach uses data acquired before historic ruptures to make and test “pre-rupture” fault traces based on the landscape morphology, geomorphology, and surficial 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. We taught a systematic mapping process to undergraduate students, graduate students, and geologic professionals.

We evaluated the approach in three ways: (1) To assess the geomorphology that best predicts future rupture, we compared the separation distance between the mapped geomorphologic features and the rupture. Of the features considered, scarps and lineaments performed best. (2) We compared the fault confidence rankings chosen by the mapper to fault confidence rankings calculated based on the mapped geomorphology near the fault traces. Accurately characterizing fault confidence is a balance between the mapper input and the calculated confidence rankings. (3) To highlight best practices and challenges of geomorphic fault mapping, we conducted listening sessions with 21 participants. We found that the terminology and mapping process vary by experience level.