Deep-ocean researchers target tsunami zone near Japan
Monday, 01.21.2008, 05:30am (GMT)
Rice University Earth scientist Dale Sawyer and colleagues last month
reported the discovery of a strong variation in the tectonic stresses
in a region of the Pacific Ocean notorious for generating devastating
earthquakes and tsunamis in southeastern Japan.
The results came from an eight-week expedition
by Sawyer and 15 scientists from six countries at the Nankai Trough,
about 100 miles from Kobe, Japan. Using the new scientific drilling
vessel "Chikyu," the team drilled deep into a zone responsible for
undersea earthquakes that have caused tsunamis and will likely cause
more. They collected physical measurements and images using new rugged
instruments designed to capture scientific data from deep within a well
while it is being drilled.
The Nankai Trough is known as a subduction zone,
because it marks the place where one tectonic plate slides beneath
another. Tectonic plates are pieces of the Earth's crust, and
earthquakes often occur in regions like subduction zones where plates
grate and rub against one another. For reasons scientists don't yet
understand, plates that should move smoothly relative to each other
sometimes become locked. In spite of this, the plates continue moving
and stress builds at the points where the plates are locked. The stored
energy at these sites is eventually released as large earthquakes,
which occur when the locked area breaks and the the plates move past
one another very rapidly, creating a devastating tsunami like the one
in Sumatra and the Indian Ocean three years ago.
"Earthquakes don't nucleate just anywhere," Sawyer said. "While the
slip zone for quakes in this region may be hundreds of kilometers long
and tens of kilometers deep, the initiation point of the big quakes is
often just about five to six kilometers below the seafloor. We want to
know why.”
Sawyer said scientists with the Integrated Ocean
Drilling Program (IODP) plan to return to the Nankai Trough aboard the
Chikyu each year through 2012, with the ultimate goal of drilling a
six-kilometer-deep well to explore the region where the quakes
originate. If they succeed, the well will be more than three times
deeper than previous wells drilled by scientific drill ships, and it
will provide the first direct evidence from this geological region
where tsunami-causing quakes originate.
The drilling done by Sawyer and colleagues marked the beginning of
this massive project, which IODP has dubbed the Nankai Trough
Seismogenic Zone Experiment, or NanTroSEIZE. In addition to the
objective of drilling across the plate boundary fault, NanTroSEIZE
scientists also hope to sample the rocks and fluids inside the fault,
and they want to place instruments inside the fault zone to monitor
activity and conditions leading up to the next great earthquake.
"The Chikyu is a brand new ship -- the largest science vessel ever
constructed -- and it uses state-of-the-art drilling technology,"
Sawyer said.
The Chikyu is the first scientific drill ship to incorporate riser
drilling technology. Pioneered by the oil industry, a riser system
includes an outer casing that surrounds the drill pipe to provide
return-circulation of drilling fluid to maintain balanced pressure
within the borehole. The technology is necessary for drilling several
thousand meters into the Earth.
Source: Rice University
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