Japan deep-sea drilling boat casts off to find quakes

from apperspective.net: 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
scientists weighed anchor on Japan’s deep-sea drilling vessel Chikyu,
heading for a spot in the ocean off the Kii peninsula, southwestern
Japan, and a fracture in the Earth’s crust known as the Nankai Trough (pictured).


Experts
have warned 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.

Japan’s government last year unveiled a worst-case scenario, warning a big quake in the area
could kill over 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 metres (2.2 miles) 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 metres 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 (JAMSTEC).

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 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 mega-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 — has been
anchored in central Shimizu port, and was open to foreign press this
week ahead of the mission.

The vessel, built in 2005 at a cost of
$500 million, is equipped with a 121-metre (400-foot) drill tower that
can descend 7,000 metres below the seabed, nearly three times as deep as
its predecessors.
It depends on satellite location systems with
pinpoint accuracy that allow its captain to know exactly where the ship
is in relation to the Earth’s crust.

Seismically-active Japan experiences 20 percent of the world’s major earthquakes every year.

Building
standards are high and its people are well-practised at taking cover
when quakes strike, meaning damage and death tolls are often much lower
than in other parts of the world.

But its proximity to major tectonic faults means the risk is ever-present.

On March 11, 2011, the northeastern region was hit by a 9.0 magnitude quake, which triggered a huge tsunami.

More
than 18,000 people were killed when the waves swept ashore. They also
swamped cooling systems at a nuclear plant in Fukushima, sending
reactors into meltdown and sparking the world’s worst atomic accident in
a generation.