Slippery Clay at Fault in 2011 Japan Earthquake: Page 3

The drilling site offshore of Japan, where researchers pierced through the plate boundary that caused the 2011 Tohoku earthquake.

Why so weak?

The studies add more evidence to a growing body of research that faults may get very weak when they slip at very high speeds, Fulton said. This behavior has been seen in laboratory experiments with rocks from fault zones, and computer simulations. However, alternative models have been proposed to explain the unusual behavior of the Tohoku earthquake.

"The [drilling project] findings bring us closer to determining which of these views is correct," Kelin Wang, a geophysicist with the Geological Survey of Canada who was not involved in the study, wrote in a commentary on the studies, also published today in Science.

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The studies are only the first of many to come from the drilling project. Scientists are analyzing fossil and ash layers from the drill core to correlate the rocks with layers elsewhere in the Pacific. Another project involves measuring the effects of aftershocks on the fault, via the borehole used to monitor temperature. Researchers also plan to search for the dragon-skin clay in other subduction zones, and model how it changes its behavior deeper in Japan's subduction zone. Finally, there are plans to compare the friction results to other active fault drilling projects in Costa Rica, China and Taiwan. [The 10 Biggest Earthquakes in History]

And scientists still have to figure out how the weak dragon-skin clay can store seismic energy between earthquakes, or if another mechanism is at work.

"There's been a lot of conversation and argument, because the clay is so weak it's impossible to imagine it building up a lot of elastic strain to drive earthquakes," Rowe said. "In the 21st century, we've had less than 10 magnitude-9 earthquakes, and each one teaches us something completely new."

Original article onLiveScience's OurAmazingPlanet.

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