Slippery clay a factor in Japan’s Tohoku-Oki 2011 earthquake

A thin layer of slippery clay was major contributor to the fault rupture that generated the 2011 Tohoku-Oki earthquake and subsequent tsunami, according to new sea floor drilling research.

The Chikyu research drilling vessel.

A series of three studies, published today in Science, describe rock samples retrieved from the rupture zone. Their collective observations suggest that a critical reason for the quake’s monstrosity was that the associated fault was thin (just millimeters in the slip zone) and weak (made largely of clay sediments).

Dr Virginia Toy from the Department of Geology at Otago University says the research will help scientists to work out if other major faults around the Pacific Rim, including beneath New Zealand’s east coast, could generate similarly large tsunami due to very large slippage during future earthquakes.

“If our local subduction megathrust faults have similar composition and fabric, we should be aware they may generate large tsunami when they do fail in future earthquakes,” she says.

Dr Toy is a co-author on one of the studies and was part the team retrieving core samples by drilling into the fault off the Japanese coast in 2012 from the International Ocean Discovery Program (IODP) research vessel Chikyu.

Media coverage of the research includes:

Radio NZ: Reason for massive scale of Japan quake discovered Fine sand led to Fukushima tsunami – NZ researchers
New Zealand Herald: Key factor in triggering Fukushima tsunami identified – study
US News and World Report: Slippery, Weak Fault Zone Caused Massive 2011 Japan Tsunami
Phys.Org: Slippery fault unleashed destructive Tohoku-Oki earthquake and tsunami
Toronto Star: Japan’s tsunami: How clay on the Pacific floor could raise the risk of another large earthquake Fine clay linked to Japan tsunami
Surprising Science: Fault That Caused Japan’s 2011 Earthquake Is Thin and Slippery
LiveScience: Slippery Clay at Fault in 2011 Japan Earthquake