Neotectonics of the Magallanes‑Fagnano fault system in Fuegian Patagonia based on high‑resolution seismic profiles and geomorphic markers

The Magallanes–Fagnano Fault System (MFFS), located at the southern tip of Patagonia, is part of the transform plate boundary between the Scotia and South American plates. Modern deformation along the fault system has been mostly studied on land, such as in the eastern region of Lago Fagnano. Furthermore, previous studies have primarily focused on the analysis of co-seismic deformation, while the long-term landscape response to neotectonics has not been addressed in detail. This work aims to identify and characterize active fault segments within the lake sediments and investigate the imprint of deformation in the surrounding landscape. To achieve this, we integrate high-resolution seismic profiles acquired in Lago Fagnano with a morphometric analysis of the hydrographic basin. These segments show subaqueous ruptures affecting the lacustrine sediments reaching the lake floor, indicating recent deformation episodes. Most of the recognized faults are sub-vertical or dip steeply (> 60°) to the south and show vertical offsets that range from 4 to 17 m. The morphometric analysis is consistent with the overall southward dip of the MFFS and indicates a hydrographic rejuvenation towards the north of the lake. In addition, the ruptures of the fault system can be correlated with the deformation observed on land, resulting in a ~ 150 km long segmented surface rupture zone that might be consistent with the rupture length estimated for the 1949 M7.5 earthquake doublet.