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2011 Japan tsunami was triggered by world's largest fault slip

By Catholic Online (NEWS CONSORTIUM)
December 6th, 2013
Catholic Online (www.catholic.org)

Tens of thousands of lives were lost or swept away to sea in a devastating tsunami in Japan in April of 2011. The earthquake since then has been the subject of intense study. In a series of simultaneous scientific conclusions that were recently published, scientists agree the disaster was the result of the world's largest fault slip. Scientists also say the the lengthy trench still has the capacity to surprise the world.

LOS ANGELES, CA (Catholic Online) - The fault, or the boundary between two tectonic plates-in the Japan trench slipped by as much as 164 feet. Other large magnitude earthquakes, including the 9.1 Sumatra event in 2004, resulted in a 66-to-82 foot slip in the fault.

"We've never seen 50-meter [slips]," Kelin Wang, a geophysicist with the Geological Survey of Canada in British Columbia says.

One would have to reach all the way back to 1960 to see a comparable slip in the Chilean earthquake of that year. Wang, not involved in the research, based his observation on the limited data recorded from that earthquake, when the fault slipped by 98 to 131 feet.

The majority of the movement occurred horizontally, he explained. The plates were wedged together at this trench. The horizontal displacement still managed to thrust up enough seawater to produce the deadly tsunami that washed over Japan.

One aspect of the disaster, the resulting lubrication, specifically involving clay, was the key to such massive movement.

The two tectonic plates involved are the Pacific plate, on which the Pacific Ocean resides, and a portion of the North American plate, on which parts of Japan sit, Frederick Chester, a geophysicist at Texas A&M University in College Station, and lead author of one of the studies says.

A thick layer of clay sits atop the Pacific plate, which is getting dragged under a portion of the North American plate. While Pacific plate dives into a trench off the coast of Japan, small portions of the clay get smeared along the plate boundary. "We think that's responsible for allowing the incredibly large slip we observed near the trench," Chester says.

When two plates collide, there is friction. You can think of friction like a brake, Chester explained. "But clay almost removes any braking properties."

Thanks to The Japan Trench Fast Drilling project, experts were able to take core samples of sediment and rock from the trench-located in 23,000 feet of water-thanks to a sophisticated drilling ship.

Not only did scientists find evidence of this thin layer of lubricating clay, but experts were also able calculate how much heat and friction was involved.

It's difficult to say whether something like this could happen elsewhere, Wang says, because no other submarine trench has as many instruments monitoring it. "Nowhere else do we have such a massive monitoring system."

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