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

addition, Lake Llanquihue experienced a drastic lake level rise (~50m) about 1 kyr ago (Benischke, 2024), affecting the sediment dynamics and sediment supply to potential turbidity currents triggered by earthquake shaking. Despite this natural variability between the lake systems, we observed that the 1737 imprint is relatively thicker and more extensive than the 1837 imprint in the northern part of the transect (Moernaut et al., 2014), whereas the southern part shows a relatively larger 1837 imprint. This finding is consistent with the distribution of the historically-reported evidence for these two events and confirms that the 1837 event ruptured the southern two-thirds of the Valdivia segment, whereas the 1737 event ruptured the northern third. Fig. 2: Correlation of seismo-turbidites in three representative cores from the new lake sites. From left to right: Ranco (RAN), Rupanco (RUP) and Llanquihue (LLAN). The Riñinahue and Mil Hojas tephras serve as regional markers. X-CT image (left; dark = low density) and histogram- equalized color image (right) are shown for each core. No tsunami was reported for the 1737 event, and it was therefore inferred to be a deep megathrust rupture (Cisternas et al., 2017). A recent study on the Chaihuín coastal marsh (14 km NNE of Laguna Gemela West) challenged that hypothesis (Hocking et al., 2021), as a potential 1737 tsunami deposit was identified, although the dating uncertainty is rather large (1600- 1820). The more precise age-depth model at Laguna Gemela West (Fig. 3) reveals a tsunami deposit in 1679-1758 and allows us to propose that the 1737 event generated a local tsunami. For this, it must have ruptured (at least) the updip part of the megathrust.