Photo/IllutrationA drilling rig rises 130 meters high from the bottom of the Chikyu scientific research vessel. (Asahi Shimbun file photo)

  • Photo/Illustraion

Researchers studying the mechanism of earthquakes along the Nankai Trough south of Japan have abandoned their goal of drilling about 5,200 meters into the seabed to reach a plate boundary fault.

The project, the first of its kind in the world, is part of the International Ocean Discovery Program, which involves 25 countries. Around 6 billion yen ($54 million) was set aside for the drilling mission off the Kii Peninsula.

However, the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) said Feb. 8 that its Chikyu deep-sea drilling vessel will “likely be unable” to reach the planned depth.

The Chikyu in November began drilling at a depth of 3,058.5 meters below the seafloor, which had been attained during a previous mission.

It reached a depth of 3,262.5 meters in December, but the drill stopped going further downward as scheduled, presumably because of the complicated geology in the submarine depression.

A fault defining the boundary between a continental tectonic plate and the Philippine Sea Plate is believed to lie at the targeted depth of 5,200 meters.

But officials decided it will be difficult to reach the plate boundary fault.

“Currently available technologies did not allow us to deal with complicated geology, despite all the experience and wisdom we have brought together,” said Shinichi Kuramoto, director-general of the JAMSTEC Center for Deep Earth Exploration. “It’s all too bad, but I believe what we have learned this time will turn out useful in the future.”

The Chikyu research vessel is designed to drill up to 7,000 meters into the seabed.

The drilling work is continuing, and the crew are expected to reach a maximum depth possible to gather data and specimens before ending the mission in March.