Drilling vessel heads out to explore Nankai Trough quakes

AFP-JIJI

A Japan-led team of seismologists set off Friday on a mission to drill deep beneath the seabed in a search for the origin of earthquakes.

The deep-sea drilling vessel Chikyu departed from Shimizu, Shizuoka Prefecture, bound for the fracture in the Earth’s crust known as the Nankai Trough, at a point off the Kii Peninsula.

Experts have warned that the trough, which marks the place where the Philippine Sea plate slides under the Eurasian plate, is the likely source of a monster earthquake sometime in the near future.

The government unveiled a worst-case scenario last year warning a big quake in the area could kill more than 320,000 people, dwarfing the March 11, 2011, quake-tsunami disaster.

In its four-month mission, the latest stage of a multi-year project that began in 2007, the team plans to drill 3,600 meters down and take samples from the crust.

They will also be readying for another trip next year in which they hope to get 5,200 meters down, to the spot where the action actually happens.

“It would be unprecedented to drill directly into a seismogenic zone, the area believed to release great energy and cause crusts to slide along fault lines and trigger tsunami,” said Tamano Omata, a researcher for the Japan Agency for Marine-Earth Science and Technology.

Scientists want to plant sensors such as seismometers, deformation-measuring devices and thermometers in the zone, that will form part of a system called Dense Oceanfloor Network System for Earthquakes and Tsunamis (DONET), which is linked directly to onshore monitors.

“We expect to become able to monitor how the crusts move immediately before a quake hits,” Omata said.

Shinichi Kuramoto, deputy director of JAMSTEC’s Center for Deep Earth Exploration, said recent research has shown that mild earthquakes, in which the two crusts slip gently past each other, have occurred frequently over stretches of the Nankai Trough in the past five years.

He said it was possible these were precursors to a catastrophic quake.

“Directly drilling into and observing the place that may release a big quake would be a big step towards understanding the seismological mechanism,” he said.

The 56,752-ton Chikyu — “Earth” in Japanese — was open to foreign press this week ahead of the mission.

The vessel, built in 2005 at a cost of ¥50 billion, is equipped with a 121-meter drill tower that can reach 7,000 metres below the seabed, nearly three times as deep as its predecessors.

It depends on satellite location systems with pinpoint accuracy to determine exactly where the ship is in relation to the Earth’s crust.

  • http://www.sheldonthinks.com/ andrew Sheldon

    This is strange logic – “recent research has shown that mild earthquakes, in which the two crusts slip gently past each other, have occurred frequently over stretches of the Nankai Trough in the past five years”. The implication is that there is ‘less likely to be a big quake’, unless the thesis is that gentle movement has occurred in some areas, not others, so a section of crust is about to ‘correct’. The fact is that, they can’t know what is occurring along the entire strike of the trough unless seismic surveys can satisfactorily identify marker beds. They will then need to monitor every section of the trough…assuming that seismic surveys identifies ‘marker’ beds of maritime sediment which will allow them to see where there is ‘differentiated fault movement’. Its not a homogeneous system.