Record-Breaking Ocean Drilling Uncovers Earthquake Danger

New research shows fragile clay layer beneath Japan Trench played key role in extreme seafloor movement during 2011 quake

Published on Feb. 10, 2026

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New research based on samples collected from the Pacific seafloor offers a clearer picture of what caused the extreme seafloor movement and tsunami during the 2011 Tōhoku earthquake in Japan. Scientists found that a fragile, clay-rich layer just below the seafloor provided a weak surface for the rupture to reach all the way to the trench, resulting in about 130 to 200 feet of shallow slip and widespread displacement of the ocean bottom.

Why it matters

The discovery of this fragile clay layer helps explain why the 2011 earthquake was so destructive, with a rupture that reached much closer to the seafloor than typical earthquakes. This finding could allow scientists to better identify locations prone to similar 'worst-case scenario' earthquakes and tsunamis in other subduction zones around the world.

The details

The research was co-authored by NAU associate professor Christine Regalla and more than a dozen collaborators. They found that at the Japan Trench, where an oceanic plate sinks beneath Japan, the main fault zone squeezes into an exceptionally thin, clay-rich band just below the seafloor. This weak and slick layer provided a ready surface for the 2011 'megathrust' rupture to follow all the way to the trench, resulting in the extreme seafloor displacement that intensified the tsunami.

  • The 2011 Tōhoku earthquake occurred in Japan.
  • The research team drilled 26,000 feet into the ocean floor in the western Pacific and analyzed the recovered samples, which was recognized as the deepest scientific ocean drilling ever achieved.

The players

Christine Regalla

An associate professor at Northern Arizona University's School of Earth and Sustainability and co-author of the study.

Patrick Fulton

An associate professor in the Department of Earth and Atmospheric Sciences at Cornell University and co-author of the study.

Chikyu

The research vessel used by the team to conduct the deep-sea drilling expedition.

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What they’re saying

“That's equivalent to the entire area between Los Angeles and San Francisco moving 130 to 200 feet in just six minutes. We've never seen anything like that in the time we've been observing earthquakes. Based on what we understood, we didn't think that could happen.”

— Christine Regalla, Associate Professor (SciTechDaily)

“At the Japan Trench, the geologic layering basically predetermines where the fault will form. It becomes an extremely focused, extremely weak surface, which makes it easier for ruptures to propagate all the way to the seafloor.”

— Patrick Fulton, Associate Professor (SciTechDaily)

What’s next

The researchers hope their findings will help scientists better understand and forecast large-magnitude earthquakes and tsunamis by identifying locations most susceptible to shallow-slip events. This could inform policy decisions on building codes, infrastructure, and emergency planning to improve community resilience.

The takeaway

The discovery of the fragile clay layer beneath the Japan Trench that facilitated the extreme seafloor movement during the 2011 Tōhoku earthquake provides critical insights that could help predict and prepare for similar 'worst-case scenario' events in other subduction zones around the world.