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

328 PATA Days 2024 M E T H O D S Our research strategy consists of i) systematic mapping of event deposits over the last 800 years based on subbottom profiles and numerous short sediment cores; ii) deriving of quantitative measures of imprint size (e.g., cumulative turbidite thickness, number of subbasins with turbidites, etc); and iii) establishing and applying scaling relationships between sedimentary imprint “size” and ground motion parameters (e.g. seismic intensity, PGA, PGV); and iv) comparing the results to historical evidence and coastal paleoseismic and paleotsunami archives. The latter two points are ongoing topics of research. For the inland lakes, turbidites were identified in short sediment cores based on their homogenous/graded nature compared to laminated background sediments (Fig. 2). This analysis was based on medical X-ray CT scans, macroscopic observations and magnetic susceptibility profiles. Age control for the 1960 event was provided by identification of the 137Cs peak (mid- 1960s) just above the turbidites, and a tephra related to the 1907 Riñinahue maar eruption that can be found in several lakes W-SW of the volcanic field. Age control for older events relies on 14C ages and -more importantly- the geochemical identification of the Mil Hojas tephra (Fontijn et al., 2016), which originated at the Puyehue Volcano and is dated to 1106-1266 (Benischke, 2024). It forms the most important marker tephra in our entire transect and separates the turbidites related to prehistorical full ruptures dated to ~1320 and ~1130 (Moernaut et al., 2014). In the northern part of the transect, turbidite ages are further constrained by counting of annual laminations (varves). Laguna Gemela West (~ 5 m asl, 17.5 m deep) is separated from the Pacific Ocean via a 400 m long winding channel bordered by 30 m high sand dunes. Tsunami deposits were identified based on their coarse grain size and high Ca content inferred from X- ray fluorescence (XRF) core scanning (Fig. 3). Both parameters increase in the sediment cores that are closer to the outflow of the lake and thus closer to the ocean. The age-depth model is based on the 137Cs peak and 14C dates. R E S U LT S / D I S C U S S I O N The new lacustrine paleoshaking records from Lakes Ranco, Rupanco and Llanquihue reveal a consistent and large-scale imprint of the 1960, 1575 and ~1320 events (Fig. 2), which were inferred to represent full ruptures of the Valdivia Segment. Turbidites related to the partial ruptures of 1837, 1737 and ~1460 can be found at the base of slopes, especially below those slopes that are more sensitive to seismic shaking (e.g., steep slopes and deltaic slopes). Overall, it seems that the studied basins in Lake Ranco are more sensitive recorders of past shaking than the studied basins in Lakes Rupanco and Llanquihue. This may be related to differences in i) the generation of seismo-turbidites governed by sedimentation rate (Wilhelm et al., 2016), sediment type and slope gradient, and ii) whether the turbidity current reached the core site, depending on the transported material, the basin morphology and the distance to the core location (Moernaut et al., 2014). In