A high-resolution seismic investigation of active faulting in lakes of Patagonia

BRAN, DONALDO M.; LOZANO, JORGE G.; ALMARÁZ, FERNANDO; WINOCUR, DIEGO; RESTELLI, FLORENCIA BELÉN; BUNICONTRO, S.; LODOLO, EMANUELE; BARADELLO L.; GUTIERREZ, YASMIN SOLEDAD; TASSONE, ALEJANDRO

Bariloche

Congreso; IAL IPA 2022; 2022

International Association of limnogeology y International Paleolimnology Association

Subaqueous lacustrine deposits are a valuable tool for the characterization of tectonic deformation since they offer decisive cross-sections with thick and usually well-preserved sedimentary records where to look for markers. This fact plays a key role in places where direct morphological evidence is lacking due to high erosion and/or slow deformation rates or is concealed by dense forests or extensive water bodies, as is the case of Patagonian Andes. This work presents the results of high-resolution seismic research in lacustrine subaquous deposits that led to the identification and characterization of active structures in two lakes encompassed within different tectonic settings. Lago Fagnano, located in the Fuegian Patagonia, runs along the active Magallanes – Fagnano transform fault system. The area is characterized by shallow low-magnitude seismic activity with large historical earthquakes, such as the Mw 7.5 1949. This event generated coseismic ruptures identified onshore, although their full extension remains uncertain. Seismic reflection data in the lake revealed a series of fault ruptures affecting glaciolacustrine and lacustrine deposits, several of which reach the lake-floor suggesting these could represent the offshore continuation of the 1949 rupture. In addition, seismic data shows how deformation is distributed along different fault segments, representing along-strike variations of deformation. On the other hand, Lago Argentino is a large proglacial lake located in the Austral Patagonian Andes foreland. Despite the seismic activity recorded in the area, no studies regarding the neotectonic activity have been carried out so far. We have identified subvertical faults within the post-glacial lacustrine sediments of Rico and Sur arms of the lake that constitute the first evidence of active tectonics in the area. Subaquous faults could be correlated with onshore geomorphic markers that affect basement rocks. The identification and characterization of active potentially seismogenic faults is a key step to a thorough hazard assessment in Patagonia, where these types of studies are yet limited. Not only to evaluate future fault ruptures but also to investigate the occurrence of associated geohazards such as soil liquefaction, landslides and associated tsunami.