Proceedings of the 12th International INQUA meeting on paleoseismology, active tectonic and archaeoseismology

Tierra del Fuego is a natural laboratory for paleo seismological studies due to being heavily affected by glacial processes during the Quaternary. Numerous features and structures originating from glacial and post-glacial activity (paleo-meanders, moraines, alluvial terraces), which also act as geomorphological markers, preserve ruptures associated with the MFF (e.g., Lodolo et al., 2003; Costa et al., 2006; Waldmann et al., 2011; Onorato et al., 2020; Sandoval & de Pascale, 2020; Roy et al., 2020; 2023; Vassallo et al., 2024). However, to date, only a few paleo seismological studies have been conducted in the area. Costa et al. (2006) reported evidence of at least three paleo-earthquakes occurring during the last 8 kyr, suggesting a maximum average recurrence within an interval of 2 to 3 kyr. On the other hand, based on mass-wasting events in Lake Fagnano over the last 11 kyr, Waldmann et al. (2011) proposed a maximum average seismic recurrence interval between 350 and 850 years along the MFF. Recently, Roy et al. (2023) reported an average recurrence of 1080 ± 150 years for the last 2 kyr. There are records of two major historical earthquakes that occurred in 1879 and 1949 in Tierra del Fuego. The magnitude of the 1879 earthquake is poorly known, Lomnitz (1970) proposes Mw 7-7.5. The Fig. 1: a) Geodynamic setting of the study area. b) Regional tectonic setting showing the boundary of the MFF. White rectangle shows the location of our study area around Lake Fagnano in Chilean territory (Figure 2). best-documented event is the one from 1949, which is the largest recorded event in this area, registering two shocks of similar magnitude on the same day followed by multiple aftershocks (Febrer et al., 2000; Bujalesky, 2007; Cisternas & Vera, 2008). Various authors (e.g., Costa et al., 2006; Pedrera et al., 2014; Roy et al., 2020; 2023) have conducted studies along this fault in Argentina. Roy et al. (2020) reported surface ruptures with a maximum left lateral horizontal offset of 6.5 ± 0.5 m, extending over 50 km from the eastern edge of Lake Fagnano to Malengüeña Hill, towards the Atlantic Ocean. It is well-known that the fault continues towards the west beneath Lake Fagnano, but its whole extension and continuity remain uncertain. In fact, little is known about the deformations that affected the Chilean sector. In this study, we present evidence of co-seismic rupture caused by the 1949 earthquake on the western edge of Lake Fagnano in Chilean territory, an area in which the 1949 rupture has not yet been described. MORPHOTECTONIC EVIDENCES In the Chilean sector, the most direct observations of the fault’s behaviour during recent earthquakes, such as the determination of lateral offset and kinematics, is difficult due to the dense forest that covers most of onshore outcrops. Despite this, we identified at