In the Kuril Trench off the coast of Hokkaido, where the government assumes that the possibility of a huge earthquake is imminent, the boundary between the land-side and sea-side plates near the seafloor hardly moves, and there are areas where it seems to be stuck. A research group at Tohoku University and others has compiled the results of research that suggests there is.
The research group plans to proceed with further observation and analysis in the future, as there is a risk that strain will accumulate in this region and cause a huge tsunami if it shifts.
Three years ago, a research group consisting of Tohoku University, Hokkaido University, and the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) began constructing three submarine base stations on either side of the Chishima Trench, where the ocean-side plate on the ocean floor off the coast of Nemuro in eastern Hokkaido subducts into the land-side plate. They were installed at several locations, and the changes in the seafloor were observed by sending sound waves from ships on the ocean and measuring the time it took them to bounce back.
As a result, it was confirmed that all three base stations moved about 7 centimeters to the land side in one year.
Based on this result, the research group believes that the plates are stuck together at the shallow part near the seafloor of the plate boundary off the coast of Nemuro.
The research group plans to continue observation and analysis from next year onwards, as there is a risk that strain will accumulate in this region and cause a huge tsunami if it shifts due to an earthquake.
Fumiaki Tomita, assistant professor at the International Research Institute of Disaster Science, Tohoku University, who conducted the survey, said, ``If the plate is stuck at a shallow boundary, there will be concerns about a huge earthquake and tsunami like the Great East Japan Earthquake. We need to be careful,” he said.