MBARI’s advanced underwater technology reveals history of earthquakes in the Pacific Northwest

Extending from California to Canada, the Cascadia Subduction Zone has a history of producing mega earthquakes. Understanding the paleo-seismic history of this region is critical for helping coastal communities in the Pacific Northwest plan for future earthquakes and tsunamis.

Members of MBARI’s marine operations prepare a robotic submersible for deployment. The submersible is in the center of the frame, with a yellow float and black metal instrumentation below. It is suspended from a white metal crane above the open silver metal doors of a moon pool. To the left is a crew member observing deployment, and to the right is a crew member operating the crane. In the background are various pieces of scientific and maritime equipment, illuminated by a skylight overhead. — MBARI’s collaboration with USGS leverages our advanced technology to map and sample geologic deposits and fault ruptures in the deepest parts of the Cascadia Subduction Zone. Image: Madison Pobis © 2021 MBARI

Since 2020, researchers in MBARI’s Continental Margin Processes Team and Seafloor Mapping Lab have been collaborating with geologists from the USGS Pacific Coastal and Marine Science Center to study the geological history of the Cascadia Subduction Zone using advanced underwater technology.

Earthquakes trigger underwater landslides that create sediment layers that preserve the history of seismic activity. Deposits known as turbidites form when earthquakes destabilize sediment on the continental slope, sending landslides downslope to settle on the abyssal seafloor. Since other extreme events, like floods, can also leave behind turbidites channeled down submarine canyons, the team sought to map and sample deposits in deeper water and isolated from canyons to distinguish those produced during major earthquakes.

During three expeditions in 2020 and 2021, the team used MBARI’s seafloor mapping autonomous underwater vehicle to conduct detailed surveys of the southern Cascadia Subduction Zone offshore of Northern California and leveraged MBARI’s remotely operated vehicle Doc Ricketts to collect sediment samples from specific research sites and look for deposits of abyssal turbidites.

The black metal robotic arm of a deep-sea submersible places a silver metal cylinder covered in fine brown sediment into a rack of 12 sediment samples. The sediment samples are in tall, thin silver metal cylinders cradled by a short white plastic tube. The background is brown muddy seafloor fading to black water on the horizon. — A motor generates high-frequency vibrations that allow the vibracore to collect samples from water-saturated sediment. These samples contain a record of seafloor sediments over time, including turbidites deposited during a landslide following a mega earthquake. Image: © 2021 MBARI

The team’s research revealed that during major earthquakes, widespread failures occur on the lower continental slope, producing thick, coarse deposits close to the slope. Farther offshore, these same deposits fan out to generate complex, layered turbidites that spread across the abyssal plain. Together, the deposits form a continuous, event-by-event record of Cascadia’s great earthquakes. USGS and MBARI researchers published their findings from this work in the scientific journal Science Advances this week.

By clarifying how and where abyssal turbidites are generated, this research strengthens confidence in using these deposits to reconstruct long-term seismic histories and ultimately helps coastal communities assess risks of future earthquakes and tsunamis.

Research Publication:

Hill, J.C., J.T. Watt, C.K. Paull, D.W. Caress, D.S. Brothers, K. Arizmendi, R. Gwiazda, J. Kluesner, E. Lundsten, N.M. Nieminski, J.S. Padgett, J.B. Paduan, and G. Snyder. 2026. Widespread abyssal turbidites record megathrust earthquake-triggered landslides and coseismic deformation in the Cascadia subduction zone. Science Advances, 12: eadx6028. https://doi.org/10.1126/sciadv.adx6028