Slippery clay responsible for 2011 Japan Earthquake

Dec. 6 (UPI) -- Slippery clay lining a weak fault zone along the coast of Japan was responsible for the unusual earthquake and consequent tsunami that hit the country in March 2011.

Three studies published Thursday in the journal Science, analyzing clay retrieved in 2012 the international Japan Trench Fast Drilling Project, indicate the reason a seafloor plate slid a remarkable 165 feet in the Tohoku-Oki earthquake is because the clay provided almost no friction.

The clay, which researchers said looked like the scales of a dragon, caused the exaggerated slipping of the Pacific plate and North American plate, which meet off the coast of Japan.

"That large slip at shallow depths contributed to the tsunami that caused so much damage in Japan," said Patrick Fulton, a researcher at the University of California, Santa Cruz, in a statement. "Usually, these earthquakes don't rupture all the way to the surface."

The earthquake occurred in a subduction area, where one plates dives below another. The typical displacement these plates undergo is close to 66 feet, and the 2011 earthquake was more than twice that. The researchers had to dig close to half a mile below the sea floor investigate why the impact was so large.

Researchers found that the fault line is thin, around 5 meters, and lined with a very slick clay, making the fault resistant to friction. This could help explain why the slip was so exaggerated.

"It's the slipperiest clay you can imagine," said Christie Rowe, a geologist at McGill University, in a statement. "If you rub it between your fingers, it feels like a lubricant."

Researchers are now investigating whether other subduction zones near Alaska and Russia may also have similar clay deposits and potentially lead to a similar earthquake.

[Science] [University of California at Santa Cruz]