Soft sediment deformation by Kelvin Helmholtz Instability: A case from Dead Sea earthquakes

The standard explanation for soft sediment deformation is associated with overturn of inverted density gradients. However, in many cases, observations do not support this interpretation. Here we suggest an alternative in which stably stratified layers undergo a shear instability during relative sliding via the Kelvin-Helmholtz Instability (KHI) mechanism, triggered by earthquake shaking. Dead Sea sediments have long stood out as a classical and photogenic example for recumbent folding of soft sediment. These billow-like folds are strikingly similar to KHI structures and have been convincingly tied to earthquakes. Our analysis suggests a threshold for ground acceleration increasing with the thickness of the folded layers. The maximum thickness of folded layers (order of decimeters) corresponds to ground accelerations of up to 1 g. Such an acceleration occurs during large earthquakes, recurring in the Dead Sea.