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

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

Congreso; IAL-IPA 2022 Lakes, Memories of the Landscape; 2022

Subaqueous lacustrine deposits are a valuable tool for thecharacterization of tectonic deformation since they offer decisivecross-sections with thick and usually well-preserved sedimentary records where to look formarkers. This fact plays a key role in places where direct morphological evidence is lackingdue to high erosion and/or slow deformation rates or is concealed by denseforests or extensive water bodies, as is the case of Patagonian Andes. Thiswork presents the results of high-resolution seismic research in lacustrine subaquousdeposits that led to the identification and characterization of activestructures in two lakes encompassed within different tectonic settings. LagoFagnano, located in the Fuegian Patagonia, runs along the active Magallanes –Fagnano transform fault system. The area is characterized by shallowlow-magnitude seismic activity with large historical earthquakes, such as theMw 7.5 1949. This event generated coseismic ruptures identified onshore,although their full extension remains uncertain. Seismic reflection data in thelake revealed a series of fault ruptures affecting glaciolacustrine andlacustrine deposits, several of which reach the lake-floor suggesting thesecould represent the offshore continuation of the 1949 rupture. In addition,seismic data shows how deformation is distributed along different faultsegments, representing along-strike variations of deformation. On the otherhand, Lago Argentino is a large proglacial lake located in the AustralPatagonian Andes foreland. Despite the seismic activity recorded in the area,no studies regarding the neotectonic activity have been carried out so far. Wehave identified subvertical faults within the post-glacial lacustrine sedimentsof Rico and Sur arms of the lake that constitute the first evidence of activetectonics in the area. Subaquous faults could be correlated with onshoregeomorphic markers that affect basement rocks. The identification andcharacterization of active potentially seismogenic faults is a key step to athorough hazard assessment in Patagonia, where these types of studies are yetlimited. Not only to evaluate future fault ruptures but also to investigate theoccurrence of associated geohazards such as soil liquefaction, landslides andassociated tsunami.