Paleoseismic Evidence of Recent Co‐Seismic Ruptures in Western Tierra del Fuego, Chile

The Magallanes‐Fagnano fault (MFF) in Tierra del Fuego (TDF) is a major left‐lateral transform boundary between the South American and Scotia plates. While surface ruptures associated with the 1949 earthquakes have been documented in Argentina east of the Fagnano Lake, their extension to the west remained uncertain. In this study, we present new paleoseismic and morphotectonic evidence of recent ruptures along the western edge of Lake Fagnano in Chile, revealing that the rupture from the 1949 event extended over 150 km. Field mapping and structural analyses reveal surface ruptures related to the 1949 earthquake. Geological structures that were observed and mapped suggest to a main left‐lateral motion of the fault. A new paleoseismological trench analysis evidences at least three rupture events that occurred during the last 2,300 years. The timing of rupture events observed in the trench is compared with results from paleoseismological trenches in Eastern TDF, and with the chronology of mass‐wasting events in the Lake Fagnano. Data suggest a major earthquake recurrence interval of ∼1,000 years, contributing to seismic hazard assessments and the understanding of active tectonics in the southernmost Andes.