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

BRAN, DONALDO MAURICIO; WINOCUR, DIEGO; LODOLO, EMANUELE; TASSONE, ALEJANDRO ALBERTO; LOZANO, JORGE GABRIEL; RESTELLI, FLORENCIA BELEN; BARADELLO, LUCA; FERNANDO ALMARÁZ; BUNICONTRO, STEFANIA; GUTIERREZ, YASMIN S.

Bariloche

Congreso; IAL IPA Joint Meeting 2022; 2022

International Association of Limnogeology

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