Surficial sediment remobilization by shear between sediment and water above tsunamigenic megathrust ruptures: Experimental study

Abstract

Large subduction earthquakes can rupture the shallow part of the megathrust with unusually large displacements and tsunamis. The long duration of the seismic source and high upper-plate compliance contribute to large and protracted long-period motions of the outer upper plate. The resulting shear stress at the sediment-water interface in, for example, the Mw 9.0 2011 Tohoku-Oki earthquake could account for surficial sediment remobilization on the outer margin. We test this hypothesis by simulating in physical tank experiments the combined effects of high- and low-frequency seismic motions on sediment of different properties (chemistry, grain size, water content, and salinity). Our results show that low-frequency motion during a 2011-like earthquake can entrain several centimeters of surficial sediment and that entrainment can be enhanced by high-frequency vertical oscillations. These experiments validate a new mechanism of co-seismic sediment entrainment in deep-water environments.