Dynamics of lake sensitivity to record paleoearthquakes

Large magnitude earthquakes are devastating events. Over the last two decades, more than 800,000 people were killed due to earthquake shaking and associated events (e.g., tsunamis, landslides). To better estimate earthquake probabilities and the location of future seismic events, it is crucial to have a detailed knowledge of the long-term history of large magnitude earthquakes. How often do they happen? Do they occur rather regularly or randomly in time or do they follow a certain pattern? To address these questions, lake sediments are a valuable geological archive that record and preserve paleoearthquake evidence in different ways, associated to e.g. underwater landslides or deformation of sediments. Sedimentary sequences that contain such earthquake-induced deposits not only reveal when earthquakes took place but can also provide data about the size of the earthquake (magnitude), the intensity of the shaking, and other associated hazards such as lake tsunamis. Traditional lacustrine paleoseismology assumes that earthquake-related deposits start to get created when a certain minimum shaking intensity is reached, and that this threshold remains constant over time. However, our recent studies suggest that earthquake imprint can be modified by a series of disturbance such as volcanic eruptions, climate change, and typhoons. Human activities (e.g. agriculture, deforestation) can also perturb lacustrine sedimentation and therefore, the earthquake imprint. The response of the lake to external stimuli is complex and needs to be studied in detail to assess its influence on the paleoseismic records. The DynSedPal project aims at understanding and quantifying the impact of environmental disturbances and human activities on lacustrine paleoseismic records. For that purpose, we will study the Fuji Five Lakes (central Japan) and the North Patagonian lakes (Chile). These two areas are frequently hit by large magnitude earthquakes and have been affected either by volcanic eruptions, typhoons associated with heavy rains, climate change or deforestation. Based on an extensive dataset collected during previous research projects in Japan and Chile, we will develop a multidisciplinary approach combining geophysical profiling, high-resolution geochemical and sedimentological analyses to assess short-term and long-term changes in the lake sedimentary infill following environmental or anthropogenic disturbances. This new approach will increase the accuracy and the reliability of paleoseismic studies and therefore will help in improving the seismic hazard assessments in many places around the world. 1