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

enable a regional correlation and constrain the ages, the major element concentrations of selected tephra layers were obtained with an electron probe microanalyzer (JEOL JXA-iSP100, University of Innsbruck) and compared with a regional database of tephrostratigraphic data (Fontijn et al., 2014; 2016) Moreover, dissolved oxygen, temperature and conductivity data were collected in the water column using an EXO multiparameter sonde (Ghent University) with the aim to compare and understand the evolution of these parameters in the water column over time (i.e., Villalobos et al., 2003; IFOP, 2017), and to investigate their potential impact on the sedimentary records presented here. RESULTS AND DISCUSSION The analyses of sub-bottom profiles revealed strong absorption of the acoustic signal at shallow depths in each deeper basin of the four lakes, probably due to the high gas content from the decomposition of organic matter. The western part of Cucao and Huelde Lakes shows a reduction in the penetration of the sub- bottom profiler signal, probably caused by the presence of coarse-grain sediment. Natri Lake corresponds to an elongated E-W basin with steeper N and S slopes, allowing the accumulation of coarse lithic material at their base, as evidenced by high-amplitude reflections with decreasing amplitude from N and S toward the basin centre (Fig 2A). In the cores, the background sedimentation is interrupted by successive sandy event layers with high potassium content coincident with high CT density and MagSus values (Fig. 2B). Through two radiocarbon dates and 210Pb/137Cs data, we estimated a sedimentation rate of ca.0.33 cm/yr, indicating that our short cores have high potential for recording paleo-earthquake in the area for the last ~2 kyrs. In Huillinco Lake, gas in the main basin does not allow the penetration of the seismic signal below a depth of 1.5m (Fig. 2A), which is also evidenced by the strong hydrogen sulphide odour of the shallower samples. CT images of cores located in the main basin reveal a high- (radio)density event deposit which, through the 210Pb and 137Cs data, was constrained as a product of the 1960 CE earthquake and tsunami. The relative increase of S in post-1960 sediment is interpreted as a result of saline water input. Due to the anoxic conditions, the deposition of laminated and potentially varved sediments – with absence of bioturbation - started after this event, showing a strong and sustained environmental change. For Cucao Lake, the sediment cores reveal a strong relationship with the location – depth, influence of tidal currents and floor morphology-, showing that in the deepest parts of the lake, anoxic conditions prevail, bearing the potential of varved laminations. Strong erosion or non-deposition is caused by tidal currents in some areas. The correlationof our newdatawithprevious literature (Kempf et al., 2015) allowed the identification of the 1960 CE event deposit in Huillinco Lake, which is coincident with a sulphur increase and change in the sediment density, potentially associated with the strong shallowest reflector (Fig. 2A and 2B). This is similar to the signature of the 1960 tsunami deposit in Huelde lake (Kempf et al., 2015): a strong surficial reflector linked with a sandy deposit at 21-41 cm depth, supported by the mid-1960 Cs peak just above it (Fig. 2B). To improve and constrain of the age-depth model, tephrostratigraphic analyses and new radiocarbon dates are being performed. This will provide a better understanding of the relationships among seismic events, tsunamis, and their geochemical imprints in sediments, which is essential for filling the knowledge gap in this coastal subduction zone.