Study: 'Hot spots' may up earthquake size

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SAN DIEGO, Aug. 30 (UPI) -- "Hot spots" of melting rock in fault zones can act as triggers to turn moderate earthquakes into massive temblors, U.S. seismologists say.

Scientists at the Scripps Institution of Oceanography in California said fault zones weaken in select locations shortly after a fault reaches an earthquake tipping point.

The locations have been dubbed "melt welts," and researchers say the mechanism is similar to how an ice skater's blade reduces friction by melting the ice surface just at the point of contact.

"Melt welts appear to be working as part of a complicated feedback mechanism where complex dynamic weakening processes become further concentrated into initially highly stressed regions of a fault," Scripps geoscience Professor Kevin Brown said.

The melt welts also may help explain why some slowly slipping tremor-generating events can snowball into massive earthquakes if they pass a velocity tipping point.

"The process allows highly stressed areas to rapidly break down, acting like the weakest links in the chain," Brown said. "Even initially stable regions of a fault can experience runaway slip by this process if they are pushed at velocities above a key tipping point."

Such a mechanism may have been involved in last year's magnitude 9.0 earthquake off Japan, he said.

"We thought that large patches of the fault were just creeping along at a constant rate, then all of a sudden they were activated and slipped to produce a mega earthquake that produced a giant tsunami."