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

Fig. 1: Setting of Laguna Lo Encañado with indication of historical rupture extents of megathrust earthquakes (Beck et al., 1998; Moreno et al., 2012) and historical earthquakes with an unsure source such as the 1575, 1580 and 1647 earthquakes (Cisternas, 2012; Cisternas et al., 2012). Earthquakes indicated in bright red have been shown to be recorded in Laguna Lo Encañado by Van Daele et al. (2019). The present study suggests that also the earthquakes in dark red are recorded. On the map, the location of Laguna Lo Encañado is indicated by a yellow/blue square. Bathymetry of Laguna Lo Encañado with location of the short gravity cores investigated by Van Daele et al. (2019) (black fill) and the long core studied here (yellow fill) (modified from Van Daele et al. (2019)). despite it hosted the largest earthquake on record: the 1960 Mw9.5 Great Chilean – megathrust – earthquake (Cifuentes, 1989). Moreover, Cisternas (2012) argues that the 1647 Santiago earthquake was likely an intraslab event, suggesting that they also pose a serious hazard for the country's most populated city. As records of coastal vertical land-level changes and tsunami deposits can be used to reconstruct the history of megathrust earthquakes (e.g., Dura et al., 2015; Wesson et al., 2015), they are usually not associated to intraslab earthquakes. Hence, to reconstruct intraslab earthquake history, paleoseismic records of their shaking are essential. Lake sediments have been shown to be excellent recorders of seismic shaking from different types of earthquakes in subduction zones (e.g., Molenaar et al., accepted; Praet et al., 2022). Moreover, Van Daele et al. (2019) showed that in Laguna Lo Encañado (33.7°S; 70.3°W; 2492 m above sea level), a lake in the central Chilean Andes, the turbidite imprint of megathrust earthquakes is different to that of intraplate (intraslab and crustal) earthquakes. While megathrust earthquakes induce merely, albeit thick, turbidites sourced from subaquatic slope failures, intraplate earthquakes also cause subaerial slope failures, which after erosion result in post-seismic turbidites by fluvial transport. This process is explained by the typical high-frequency content of intraplate earthquakes compared to megathrust earthquakes. Laguna Lo Encañado has a relatively large and mountainous catchment (39 km²) compared to its size (0.5 km²) and is therefore sensitive to any subaerial disturbances by seismic shaking. In the ~100 yr long record studied by Van Daele et al. (2019), the Mw8.8 2010, Mw8.0 1985 and Mw8.2 1906 megathrust earthquakes produced subaqueous- sourced turbidites, while the Mw7.1 1945 intraslab and Mw6.3 1958 crustal earthquakes also caused post- seismic turbidites with a terrestrial signature. Here, we present a ~6 m long record of Laguna Lo Encañado, going far beyond the 1 m short gravity cores studied by Van Daele et al. (2019). Although analyses are still ongoing, first results indicate that this is a promising new record that will provide new insights in central Chile’s seismic history.