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Slippery clay intensified Japan 2011 tsunami-quake

A thin layer of very fine clay with a consistency similar to some cosmetics made Japan’s tsunami-causing earthquake of 2011 much more dramatic because it acted as a lubricant, scientists say.

The narrow strip of slippery, wet clay that sits between two tectonic plates off the country’s northeast coast allowed them to shift past each other at tremendous speed and to travel much further than in most regular quakes, researchers said.

The finding sheds more light on a catastrophe that claimed more than 18,000 lives when a 9.0 magnitude undersea quake unleashed a towering tsunami that slammed into the coast, destroying whole communities and causing nuclear meltdowns at Fukushima.

Researchers say the stratum, made mostly of material as fine and moist as cosmetic foundation, is very thin, about one to five meters, compared with the 40 or so meters found at other major seismically active plate borders.

“The layer is 90 percent made of low friction clay, called smectite ― material similar to foundation, which tends to become runny and slippery,” said Kotaro Ujiie, an associate professor at Tsukuba University.

Ujiie is part of the Japan Trench Fast Drilling Project, which was launched in the immediate aftermath of the 2011 quake, using a deep-sea drilling vessel that allows scientists to bore far under the sea bed. (AFP)