Deep-sea drilling into one of the most active earthquake zones on the planet is providing the first direct look at the geophysical fault properties underlying some of the world's largest earthquakes and tsunamis. The Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) is the first geologic study of the underwater subduction zone faults that give rise to the massive earthquakes known to seismologists as mega-thrust earthquakes.
fundamental goal is to sample and monitor this major earthquake-generating zone
in order to understand the basic mechanics of faulting, the basic physics and
friction," says Harold Tobin, University of Wisconsin-Madison geologist
and co-chief scientist of the project.
Subduction zone faults extend miles below the seafloor and
the active earthquake-producing regions – the seismogenic zones – are buried
deep in the Earth's crust. The NanTroSEIZE project, an international
collaboration overseen by the Integrated Ocean Drilling Program, is using
cutting-edge deep-water drilling technology to reach these fault zones for the
we want to understand the physics of how the faults really work, we have to go
to those faults in the ocean," Tobin explains. "Scientific drilling
is the main way we know anything at all about the geology of the two-thirds of
the Earth that is submerged."
decade-long project – to be completed in four stages – will use boreholes, rock
samples and long-term in-situ monitoring of a fault in the Nankai Trough, an
earthquake zone off the coast of Japan with a history of powerful temblors, to
understand the basic fault properties that lead to earthquakes and tsunamis.
The project currently is in its second year.
zone faults angle upward as one of the giant tectonic plates comprising Earth's
surface slides below another. Tremendous friction between the plates builds
until the system faults and the accumulated energy drives the upper plate
forward, creating powerful seismic waves that make the crust shake and can
produce a tsunami. But although both shallow and deep parts of the fault slip,
only the deep regions produce earthquakes.
the first stage of the project, the team found evidence of extensive rock
deformation and a highly concentrated slip zone even in shallow regions that do
not generate earthquakes. One rock core from a shallow part of the fault
contains a narrow band of finely ground "rock flour," revealing a
fault zone between the upper and lower plates that is only about 0.08 inches
thick – roughly the thickness of a quarter.
deeper portions of the fault, the team discovered layers of displaced rock and
evidence of prolonged seismic activity that suggest a region known as the
megasplay fault is likely responsible for the largest tsunami-generating plate
fundamental goal was to understand how the faults at depth connect up toward
the Earth's surface, and we feel that we've discovered the fault zone that's
the main culprit," Tobin says.
next stage of drilling will commence this May, with plans to drill additional
boreholes into the plate above deep regions of the fault zone. In addition to
collecting cores for comparison to those from shallower parts of the fault, the
scientists will install sensors in these holes to set up a deep-sea observatory
monitoring physical stresses, movement, temperature and pressure.
Drilling Deep into Fault Zones
February 16, 2009