Impact of Mapper Experience and Data on the Quality of Geomorphic Fault Mapping

Mapping of potentially active faults is critical to characterizing earthquake processes and surface rupture hazard. Geologists map tectonic faults from remote sensing datasets by interpreting tectonic landforms formed during past earthquakes. However, evidence for faulting is often ambiguous, incomplete, and challenging to interpret. Conventional wisdom suggests that mapping skill improves with experience. In contrast, prior work has shown that experienced geologists can still miss faults and disagree on fault location. To test whether, when, and to what extent mapping improves with experience, we designed a repeat mapping experiment involving 23 participants, ranging from undergraduate students to senior professionals. Each participant created regional-scale fault maps using pre-earthquake remote sensing data and a systematic, geomorphology-based approach. While professionals slightly outperformed students, some graduate students produced similar quality maps, and all participants missed identifying tectonic landforms indicative of future ruptures. Using participant mapped fault data, we quantify inter-mapper epistemic uncertainty in fault location to be between 55 and 117 m. Our work gives insight into approaches to improve fault mapping and suggests that experience beyond a graduate student level does not significantly improve mapping results.