Analysis yields more data on possible repetition of March quake...

Stanford University research finds unusual ‘two-faced’ rupture caused Japanese destruction

The catastrophe that struck Japan in March was triggered by a sequence of unusual geologic events, according to new research by a team of Stanford University and University of Tokyo scientists.

The fault that generated the Tohoku-Oki earthquake did not fracture in the usual way, they report in the latest issue of the journal Science Express. Instead, it ruptured in a “flip-flop” fashion — first breaking westward, then eastward.

The first motion violently shook Japan, with magnitude-9 shocks. The second motion — generating magnitude-6.5 aftershocks — deformed the seafloor with such force that a huge tsunami was triggered.

Damage from the March 11 earthquake was extensive in part simply because it was so large, according to Stanford geophysicist Greg Beroza.

But the two-faced rupture made the devastation greater than it might have been otherwise, he said.

“Now that this “… has been observed in the Tohoku-Oki earthquake, what we need to figure out is whether similar earthquakes — and large tsunamis — could happen in other subduction zones around the world,” Beroza said.

The project was a collaborative effort. Stanford’s Beroza and graduate student Annemarie Baltay measured the energy released by the quake, while University of Tokyo’s Satoshi Ide modeled the slippage of the fault.

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