Inside a Tsunami Factory

Known as the Nankai Trough, the 500 mile long boundary between a pair of tectonic plates off the southwestern coast of Japan is now the focus of intense scientific attention. For a long time the Nankai Trough has produced tsunami after tsunami, and now scientists involved in the Nankai Trough Seismogenic Zone Experiment hope to find out just what makes it work.

“We can monitor the ocean all we want, but we’ll never understand why some earthquakes produce tsunamis and why others do not until we understand how faults work,” says geophysicist Nathan Bangs of the University of Texas.

So that is why the multiyear project will be the first to drill four miles down in to the plate to hopefully understand the source of these killer waves.

Last year aboard the vessel Chikyu, a Japanese science vessel, researchers took 3D seismic images of the faultzone, the point where the North American plate is subsiding with the Filipino plate. The images they retrieved helped the researchers to pick the best spot to drill. However, in their imaging, they also managed to discover new steeper faults in the rock. Bangs believes that these near-vertical faults could be the reason why the Nankai Trough produces approximately one 8+ earthquake every 150 years.

Answers are likely to filter in over the next four years, as scientists drill some 20,000 feet in to the rock below the surface of the sea. They will then drop seismometers and other varying instruments in to the holes that will allow them to monitor the fault in real time.

The drilling process begins with the Chikyu lowering a 20-inch wide, 1,000-foot tall segmented pipe over the drilling target. The ship will then drop a 12-inch wide drill bit down through the pipe, while simultaneously fluid will be pumped through the pipe to help with friction. The fluid will also carry any rock and debris that is churned up in the drilling process to the surface.

Posted by Josh Hill. Image shows travel times of Pacific tsunamis originating from earthquakes off Chile and Alaska.

Links:
http://www.popsci.com/scitech/article/2008-04/inside-tsunami-factory

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