# Widespread abyssal turbidites record megathrust earthquake-triggered landslides and coseismic deformation in the Cascadia subduction zone

## TL;DR

This study shows how underwater landslides triggered by earthquakes in the Cascadia subduction zone leave widespread sediment deposits that record earthquake history.

## Contribution

The paper links widespread abyssal turbidites to earthquake-triggered landslides and coseismic deformation in the Cascadia subduction zone.

## Key findings

- Widespread turbidites correspond to megathrust earthquake records.
- Landslides on the lower slope create mass transport deposits and offshore turbidites.
- Coseismic deformation of the outer wedge occurs during megathrust rupture.

## Abstract

Abyssal marine turbidites provide some of the longest and most spatially extensive records of subduction zone earthquake recurrence globally; however, correlation of these deposits over long distances and interpretation of synchronous emplacement requires both an understanding of the turbidite generating systems and precise dating. Here, we present an integrated suite of high-resolution bathymetry, subbottom profiles, and sediment cores from combined autonomous underwater vehicle, remotely operated vehicle, and ship-based studies at a key paleoseismic site in the southern Cascadia subduction zone. We demonstrate how widespread, earthquake-triggered landslides on the lower slope deposit discrete, proximal mass transport deposits (MTDs) that grade offshore into complex, interfingered abyssal turbidites, which correspond to records of megathrust earthquake history. We propose accretion and oversteepening of thrust folds on the lower slope both preconditions the slope to fail and provides a perpetual source of unstable material to fail during every earthquake cycle. Furthermore, we suggest the periodic and pervasive landsliding indicates coseismic deformation of the outer accretionary wedge during megathrust rupture.

Lower slope failures produce abyssal turbidites that record shaking and coseismic deformation during megathrust earthquakes.