Understanding the long-term earthquake recurrence pattern at subduction zones requires continuous paleoseismic records with excellent temporal and spatial resolution and stable threshold conditions. South central Chilean lakes are typically characterized by laminated sediments providing a quasi-annual resolution. Our sedimentary data show that lacustrine turbidite sequences accurately reflect the historical record of large interplate earthquakes (among others the 2010 and 1960 events). Furthermore, we found that a turbidite's spatial extent and thickness are a function of the local seismic intensity and can be used for reconstructing paleo-intensities. Consequently, our multilake turbidite record aids in pinpointing magnitudes, rupture locations, and extent of past subduction earthquakes in south central Chile. Comparison of the lacustrine turbidite records with historical reports, a paleotsunami/subsidence record, and a marine megaturbidite record demonstrates that the Valdivia Segment is characterized by a variable rupture mode over the last 900 years including (i) full ruptures (M w~9 .5: 1960, 1575, 1319 ± 9, 1127 ± 44), (ii) ruptures covering half of the Valdivia Segment (M w~9 : 1837), and (iii) partial ruptures of much smaller coseismic slip and extent (M w~7 .5-8: 1737, 1466 ± 4). Also, distant or smaller local earthquakes can leave a specific sedimentary imprint which may resolve subtle differences in seismic intensity values. For instance, the 2010 event at the Maule Segment produced higher seismic intensities toward southeastern localities compared to previous megathrust ruptures of similar size and extent near Concepciόn.

Seismically‐induced event deposits embedded in the sedimentary infill of lacustrine basins are highly useful for palaeoseismic reconstructions. Recent, well‐documented, great megathrust earthquakes provide an ideal opportunity to calibrate seismically‐induced event deposits for lakes with different characteristics and located in different settings. This study used 107 short sediment cores to investigate the sedimentary impact of the 1960 Mw 9·5 Valdivia and the 2010 Mw 8·8 Maule earthquakes in 17 lakes in South‐Central Chile (i.e. lakes Negra, Lo Encañado, Aculeo, Vichuquén, Laja, Villarrica, Calafquén, Pullinque, Pellaifa, Panguipulli, Neltume, Riñihue, Ranco, Maihue, Puyehue, Rupanco and Llanquihue). A combination of image analysis, magnetic susceptibility and grain‐size analysis allows identification of five types of seismically‐induced event deposits: (i) mass‐transport deposits; (ii) in situ deformations; (iii) lacustrine turbidites with a composition similar to the hemipelagic background sediments (lacustrine turbidites type 1); (iv) lacustrine turbidites with a composition different from the background sediments (lacustrine turbidites type 2) and (v) megaturbidites. These seismically‐induced event deposits were compared to local seismic intensities of the causative earthquakes, eyewitness reports, post‐earthquake observations, and vegetation and geomorphology of the catchment and the lake. Megaturbidites occur where lake seiches took place. Lacustrine turbidites type 2 can be the result of: (i) local near‐shore mass wasting; (ii) delta collapse; (iii) onshore landslides; (iv) debris flows or mudflows; or (v) fluvial reworking of landslide debris. On the contrary, lacustrine turbidites type 1 are the result of shallow mass wasting on sublacustrine slopes covered by hemipelagic sediments. Due to their more constrained origin, lacustrine turbidites type 1 are the most reliable type of seismically‐induced event deposits in quantitative palaeoseismology, because they are almost exclusively triggered by earthquake shaking. Moreover, they most sensitively record varying seismic shaking intensities. The number of lacustrine turbidites type 1 linearly increases with increasing seismic intensity, starting with no lacustrine turbidites type 1 at intensities between V½ and VI and reaching 100% when intensities are higher than VII½. Combining different types of seismically‐induced event deposits allows the reconstruction of the complete impact of an earthquake.

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Lake sediments contain valuable information about past volcanic and seismic events that have affected the lake catchment, and provide unique records of the recurrence interval and magnitude of such events. This study uses a multi-lake and multi-proxy analytical approach to obtain reliable and high-resolution records of past natural catastrophes from c. 600 year old annually-laminated (varved) lake sediment sequences extracted from two lakes, Villarrica and Calafquén, in the volcanically and seismically active Chilean Lake District. Using a combination of µXRF scanning, microfacies analysis, grain-size analysis, color analysis and magnetic-susceptibility measurements, we detect and characterize four different types of event deposits (EDs) (lacustrine turbidites; tephra-fall layers; runoff cryptotephras; lahar deposits) and produce a revised eruption record for Villarrica Volcano, which is unprecedented in its continuity and temporal resolution. Glass geochemistry and mineralogy also reveal deposits of eruptions from the more remote Carrán-Los Venados Volcanic Complex, Quetrupillán Volcano and the Huanquihue Group in the studied lake sediments. Time series analysis shows 112 eruptions with a Volcanic Explosivity Index (VEI) ≥ 2 from Villarrica Volcano in the last c. 600 years, of which at least 22 also produced lahars. This significantly expands our knowledge on the eruptive frequency of the volcano in this time window, compared to the previously known eruptive history from historical records. The last VEI ≥ 2 eruption of Villarrica Volcano occurred in 1991. We estimate the probability of the occurrence of future eruptions from Villarrica Volcano, and statistically demonstrate that the probability of a 22-year repose period (anno 2013) without VEI ≥ 2 eruptions is ≤ 1.7 %. This new perspective on the recurrence interval of eruptions and historical lahar activity will help improve volcanic hazard assessments for this rapidly expanding tourist region, and highlights how lake records can be used to significantly improve historical eruption records in areas that were previously uninhabited

Historical and paleoseismic records in south-central Chile indicate that giant earthquakes on the subduction megathrust −such as in AD1960 (M w 9.5)− reoccur on average every ~300 years. Based on geodetic calculations of the interseismic moment accumulation since AD1960, it was postulated that the area already has the potential for a M w 8 earthquake. However, to estimate the probability of such a great earthquake to take place in the short term, one needs to frame this hypothesis within the longterm recurrence pattern of megathrust earthquakes in south-central Chile. Here we present two long lacustrine records, comprising up to 35 earthquake-triggered turbidites over the last 4800 years. Calibration of turbidite extent with historical earthquake intensity reveals a different macroseismic intensity threshold (≥VII½ vs. ≥VI½) for the generation of turbidites at the coring sites. The strongest Highlights  Multi-threshold turbidite paleoseismic records in south-central Chilean lakes  Probability estimates for M w ≥ 7.7 and M w ≥ 8.6 megathrust earthquakes  Quasi-periodicity suggests a dominant role for a large megathrust asperity