http://www.livescience.com/41726-japan-earthquake-culprit-slippery-clay.html

Scientists have drilled into the subduction zone responsible for the 2011 M9 Tohoku quake and found the fault is filled with a super slippery clay that likely lubricated the fault and helps explain why it was so big.

Full story at link, but some passages that caught my eye,

"Friction during earthquakes produces massive amounts of heat at faults, just as rubbing your hands together generates warmth. The Tohoku quake was hot because it slid so far, generating a residual heat anomaly of less than 0.5 degrees Fahrenheit (0.31 degrees Celsius), Fulton reported."

"The heat signal translates to a coefficient of static friction of 0.08, according to computer simulations — the same as car tires on an icy road or 0.01 greater than a rubber shoe stepping on a banana peel."

"We're all in the business of trying to know more about the physics of earthquakes and predict them if possible. To do that, we need to know what controls how earthquakes get big and how they start and stop. This puts a constraint on that, and is some of the first real robust measurements of those parameters, especially in a subduction zone."

Brian

• Slippery Clay at Fault in 2011 Japan Earthquake