Deep-water drilling identifying strains and slips in major earthquake fault

February 16th, 2009 - 3:03 pm ICT by ANI  

Washington, Feb 16 (ANI): An international project is using cutting-edge deep-water drilling technology to identify strains and slips in the Nankai Trough, a major earthquake fault off the coast of Japan.

Known as the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE), it 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.

The 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, said 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 Earths 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 first time.

If we want to understand the physics of how the faults really work, we have to go to those faults in the ocean, Tobin explained.

Scientific drilling is the main way we know anything at all about the geology of the two-thirds of the Earth that is submerged, he added.

The 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 is currently is its second year.

During 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 two millimeters thick roughly the thickness of a quarter.

Above 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 slips.

A fundamental goal was to understand how the faults at depth connect up toward the Earths surface, and we feel that weve discovered the fault zone thats the main culprit, Tobin said.

The next stage of drilling will commence this May, with plans to drill additional boreholes into the plate above deep regions of the fault zone. (ANI)

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