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

20 PATA Days 2024 1 2 T H I N T E R N AT I O N A L I N Q U A M E E T I N G O N PA L E O S E I S M O L O G Y , A C T I V E T E C T O N I C S A N D A R C H A E O S E I S M O L O G Y ( PATA ) , O C T O B E R 6 T H - 1 1 T H , 2 0 2 4 , L O S A N D E S , C H I L E EVIDENCE OF 1949 EARTHQUAKE CO-SEISMIC RUPTURES IN WESTERN TIERRA DEL FUEGO, CHILE A B S T R A C T The Magallanes-Fagnano Fault (MFF) in the Southern Andes accommodates left-lateral motion between the South American and Scotia plates. Historical earthquakes in Tierra del Fuego, notably in 1879 and 1949, underscore its seismic activity. Several studies already described surface ruptures associated to the 1949 earthquake in Eastern Tierra del Fuego (Argentina). This study presents first evidence historical co-seismic rupture in Chilean territory. Morphotectonic evidence, including non-degraded scarps, fractures in Quaternary cover, tilted trees, supports the veryrecent activity for the fault. Dendrochronological analysis aims to corroborate these findings. Oblique fractures and pop-up structures along fault scarps indicate a complex fault behaviour. Understanding fault behaviour in the Chilean sector contributes to seismic hazard assessment in the region. I N T R O D U C T I O N The Magallanes-Fagnano Fault (MFF) is a major fault system which accommodates left-lateral motion between the Scotia and South American plates at an average speed ranging from 5.9 ± 0.2 mm/yr (Mendoza et al., 2015) to 6.6 ± 1.3 mm/yr (Smalley et al., 2003) at present. This transform plate boundary extends for nearly 3,000 km from the entrance of the Strait of Magellan in the west, in the Pacific Ocean, to the Scotia Plate subduction zone in the east, in the Atlantic Ocean (Figure 1a). In Tierra del Fuego, the fault cuts across the island for about 180 km, yet most of its extent occurs beneath Lake Fagnano, with only 10-20 km outcropping onshore in the Chilean territory of the island (Figure 1b). Ricardo Aguilera-Cortés (1) Joseph Martinod (1) Riccardo Vassallo (1) Laurent Astrade (2) Christian Sue (1) K E Y W O R D S Magallanes-Fagnano Fault, Tierra del Fuego, 1949 earthquake rupture, tilted trees, paleoseismology. (1) ISTerre, CNRS, IRD, Université Grenoble Alpes, Université Savoie Mont Blanc, Université Gustave Eiffel, Le Bourget-du-Lac, France. (2) Laboratoire EDYTEM, CNRS, Université Savoie Mont Blanc, Campus Scientifique, Le-Bourget-du-Lac, France. *Email: ricardo.aguilera@univ-smb.fr