Mapping tectonic faults is challenging because mapping approaches are not standardized and some evidence for faulting is ambiguous due to surface processes that obscure the geomorphology. We developed and evaluated a new systematized approach for mapping faults and documenting geomorphic evidence based on desktop mapping using remote sensing data. Our approach works as a teaching tool to introduce fault mapping and in industry settings to establish consistent documentation. Using our approach, a mapper maps the landscape morphology, geomorphology, and surficial geology. The mapper uses the geomorphic indicator ranking approach to document the geomorphic indicators that support faulting such as scarps, triangular facets, and deflected streams. The resulting fault maps facilitate straightforward dissemination of information and build toward more accurate depictions of fault traces, which support understanding fault processes and predicting coseismic rupture location in a future earthquake.
We evaluated our mapping approach as follows. (1) We qualified the geomorphology that best predicts future rupture location as having the lowest geomorphic indicator-to-rupture separation distance. Of the features tested, cut or offset alluvial fans, fault scarps, and lineaments performed the best. (2) We found similarities in the fault confidence rankings chosen by the mappers and those calculated from the mapped geomorphology. (3) To explore best practices in fault mapping, we conducted listening sessions with 18 participants and found that terminology and mapping process vary by experience level. More-experienced mappers tend to use more technical terms to describe the geomorphology while less-experienced mappers use vague descriptions and generalize nearby features.
