Far beneath the Pacific Ocean, inside the Japan Trench about seven kilometers down, scientists are looking for answers to what causes some of the world’s strongest earthquakes and tsunamis, as reported by the Independent.
From September to December 2024, a team of 60 scientists joined drill crews on the Chikyu, the world’s largest scientific drilling ship. The project, called IODP Expedition 405, drilled into the fault zone off Japan where the 2011 Tōhoku earthquake began.
The mission reached the “décollement,” the base of the fault that broke in 2011. Sediment and rock cores were collected to study how such destructive quakes and tsunamis are set off.
Tōhoku earthquake killed more than 18,000 people
The March 11, 2011 Tōhoku earthquake was magnitude 9.1. It created a tsunami, killed more than 18,000 people, and damaged the Fukushima nuclear plant. Losses were estimated at $235 billion. Scientists later found that the biggest slip happened close to the sea floor, not deep underground, which forced huge amounts of water upward and caused the tsunami.
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{{/usCountry}}During Expedition 405, the Chikyu drilled more than 800 meters below the sea floor into the same fault. A long-term observatory was placed inside the fault to record temperature and fluid pressure. Cores were brought up every few hours, giving researchers evidence of past quakes, tsunamis and landslides. Some layers contained clay minerals that make shallow slip easier.
The samples also revealed layers of chert, marking where ocean sediments meet the crust. Each core was scanned, tested and stored for future study.
About the project
The project returned to the same site first drilled soon after the 2011 quake, offering a rare chance to see how the fault has changed over the last decade. Data from the new observatory will help scientists build models of how earthquakes start and develop.
Researchers say the results apply beyond Japan. Other subduction zones, including those in Chile, Alaska and Indonesia, also pose risks near populated coastlines. If shallow slip can occur in those regions, hazard planning must adjust.
The goal of Expedition 405 is to better understand why the 2011 quake happened and to improve global readiness for the next major earthquake and tsunami.