Unraveling the depositional processes of megaturbidites in lakes using X-ray computed tomography 

Large, destructive earthquakes pose a significant risk to our society. Lake sediments constitute ideal natural archives of past earthquakes by virtue of the sedimentary traces they have left behind. When earthquakes trigger large and/or many landslides in lakes, the distal turbidity currents associated with these landslides can result in exceptionally thick deposits: so-called megaturbidites. The landslides usually also trigger lake tsunamis and a lake seiche (i.e. standing wave). Grain-size fluctuations that are often observed at the base of megaturbidites have been linked to oscillating water movements caused by such seiches. However, a recent study by myself and colleagues, using X-ray CT scans to reconstruct flow directions within turbidites, showed that also multiple synchronous landslides can result in such grain-size fluctuations. Here, we will study megaturbidites triggered by well-described historical events in 6 different lakes with both medical and μCT scans, combined with analyses of grain size, magnetic properties etc. This will allow to reconstruct directions and characteristics of the turbidity currents, and link the different sedimentary features in the megaturbidites to the different sedimentary processes (landslides, seiche). The results of this study will allow to better reconstruct earthquake history and coupled phenomena based on the study of megaturbidites. Furthermore, it will help assessing the risks that those earthquakes pose to our society.