QuakeScene Chile: Evaluating megathrust earthquake scenarios

South-Central Chile is located where the Pacific plate moves under the South American Continent , generating large stress at the plate contact. Accumulated energy gets suddenly released when the plates slip against each other, producing strong earthquake shaking and tsunamis. In 1960, the largest known earthquake on Earth with a magnitude of 9.5 took place in this region. Its tsunami was so massive that in addition to inundating the Chilean coastline it crossed the Pacific Ocean making victims in Japan. Historical documents and the study of sand layers deposited by past tsunamis suggest that such giant earthquakes and tsunamis previously took place in this region, but several important questions remain unanswered: how often do such giant earthquake occur? Do they occur in a regular pattern? Can the accumulated stress also be released by several smaller earthquakes? Where would such smaller events take place and what is their relationship to the giant ones? To address these questions, the QuakeScene Chile project will reconstruct the timing, location and size of great earthquakes in South-Central Chile, and this for the past 5000 years. We study the sedimentary archives on the bottom of several lakes to find and date evidence of past earthquake shaking. Such evidence comes in the form of deformed layers, underwater landslides and mud avalanches. We investigate these deposits with acoustic methods (e.g. echosounders) and by taking sediment cores. These sediment cores are analyzed in the lab for their chemical and physical properties and are dated by different methods (e.g. radiocarbon). By investigating a transect of lakes along the foot of the Andes, we aim at reconstructing the variability of earthquake occurrence in time and space. This will lead to better understanding of the patterns of great earthquakes in Chile and will form the necessary data to calculate the probability that future earthquakes of different impacts will impact different regions. To reach these objectives, we develop and apply some innovative methods to i) better date the sediments, ii) better link the results from different lakes and iii) better calibrate the relationships between strong earthquake shaking and the specific deposits in lakes. Moreover, by integrating our lake sediment results with information gained from tsunami sand layers and from sudden changes in the elevation of the coast, we obtain a comprehensive picture of the location, size and nature of past earthquakes. This project builds upon strong international collaborations (researchers from Belgium, United Kingdom, Germany, Austria and Chile) and is conducted together with Chilean experts in earthquake science and its dissemination towards policy makers and the general public.