First steps towards a fast slip rate along the Liquine-Ofqui Fault Zone in Chilean Patagonia

The transpressive Liquiñe-Ofqui Fault Zone (LOFZ) is a major crustal system of dextral faults that appear to accommodate oblique subduction along the Chilean margin, is coincident with volcanoes and geothermal reservoirs, and potentially a major source of seismic hazard. Models suggest that the dextral slip rate along the LOFZ here is at least 7 mm/yr (and perhaps underestimate due to model input limitations). Importantly, there are no direct geologic estimates of how fast these fault slip - likely due to difficult access and dense rainforest combined with recent volcanic and glacial cover. We combined airborne structure from motion (SfM) and terrestrial lidar-derived topographic data with fieldwork to map and estimate slip and slip rates along the LOFZ for the first time. SfM shows a number of dextrally displaced features and the lidar-derived digital elevation model (DEM) with a resolution of at least 0.3 m (30 cm) presented here is, we believe, the first fault-specific lidar-derived DEM dataset in Chile. DEM and field results reveal "classic" strike-slip tectonic geomorphology with two main parallel depressions (lineaments) along strike with the LOFZ, and help constrain surface width of on- and near-fault deformation. Importantly, these lineaments contain sag ponds that cut across Late-Pleistocene to recent (inferred-age based on regional dating) moraine deposits. The drainage outlet for these sag ponds is dextrally offset by 20 m. Ultimately, nearby field evidence showing concentrated shearing of the Patagonian batholith and development of fault rocks (i.e. fault breccia, cataclasite, and gouge), coincident and parallel with with our mapped traces of the LOFZ, in addition to short dextral offsets (10's of m) of fluvial features (e.g. offset channels) supports the interpretation that the LOFZ is a fast-slipping, major active crustal seismogenic structure with associated seismic hazard.