Researchers discover clues as to why the 2011 tsunami in Japan was so powerful

Some of the first data from the expedition has now been published in Science. It shows that the fault zone in the Japan Trench—the deep ocean boundary where one tectonic plate dives beneath another—narrows to a thin, clay-rich layer hidden just below the seafloor. This weak layer allowed the 2011 megathrust earthquake to spread to the trench, causing a 50 to 70-meter shallow slip that displaced large sections of the seafloor.

The cores were obtained during Expedition 405 of the International Ocean Discovery Program in 2024, during which both Ikari and Zhang were aboard the Japanese drilling vessel CHIKYU. The goal was to drill through the fault and into the sediment of the Pacific Plate. The expedition reached a total drill pipe length of 7,906 meters below sea level and was recognized by Guinness World Records as the deepest scientific ocean drilling ever performed.

“IODP Expedition 405 was very successful, and I really enjoyed the discussions during and after the expedition. With the new data from the expedition, we now have a better understanding of why the plate boundary in the Japan Trench localizes into a narrow, weak fault within clay-rich sediments, making large shallow slip more likely during great earthquakes”, says Junli Zhang. And Matt Ikari adds: “We are thrilled to be able to conduct our research on the Tohoku earthquake in order to gain new insights that would not have been possible without Exp 405.”

The expedition IODP Exp 405 has also resulted in the documentary “The Story of Stress,” produced in cooperation with Science Media NL and Tales of Ocean Science.

More here:

• https://talesofoceanscience.com/
• https://sciencemedia.nl/