Comment on “Crustal faults in the Chilean Andes: geological constraints and seismic potential” by Santibáñez et al. (2019), Andean Geology 46 (1): 32-65

Understanding the location and nature of Quaternary active crustal faults is critical to reduce both the impact of fault rupture and strong ground motions hazards (when these faults rupture causing earthquakes). It is also important for understanding how and where deformation related to plate tectonics is accommodated along geological structures (oftentimes faults and folds). In Chile, work on active tectonics in the upper crust (neotectonics or earthquake geology) is relatively new, in particular regarding fault-focused studies. Therefore, any effort to further progress in our understanding of active fault systems for the benefit of the public, and for aiding local and regional governments and the earthquake engineering and scientific community with mitigation strategies should be applauded. Demonstrating where active faults are located through careful mapping, and to determine how fast they accommodate tectonic deformation and their seismic and fault rupture hazards are key questions in neotectonics. Recently Santibanez et al. (2019) explore active fault systems in the Chilean Andes. In their paper they outline active and potentially seismogenic (i.e., earthquake producing) fault systems in the Chilean Andes through a review of the literature, seismicity, case studies (earthquakes), and modeling data and then they define potential tectonic domains for subdivision of Chile. These domains were suggested to allow “a first-order approach for seismic potential assessment” (Santibanez et al., 2019). The three subdivisions they suggest, i.e., domains are the External Forearc, Inner Forearc and Volcanic Arc, were proposed based on several fault parameters (e.g., fault length), case studies, the morphotectonic setting and seismicity. Their paper generates a great foundation to build upon for both the active tectonics and geological hazards community, in addition to being useful for potential end users such as the Chilean local and national government from a planning perspective. Although the Santibanez et al. (2019) paper takes steps in the right direction, and should be considered an important contribution to the scientific community, this comment addresses three potential issues with their analysis and conclusions that should be reflected upon by the seismic hazard and active tectonics community. These ideas are summarized below and expanded on in detail thereafter.