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| Posté le 30-08-2012 à 11:28:57 |
|Des scientifiques (Kevin Brown, Yuri Fialko) ont découvert le mécanisme qui augmente la magnitude des tremblements de terre. |
LA JOLLA - Scientists have discovered the mechanism in fault lines that can increase the magnitude of earthquakes, the Scripps Institution of Oceanography announced today.
The study, to be published in Thursday's edition of the journal nature, explains how a reduction in friction in rupturing faults leads to a snowball effect, resulting in events like the magnitude-9.0 quake off Japan in March 2011, according to Scripps.
The process weakens high-stress areas of the fault, said Scripps scientists Kevin Brown and Yuri Fialko. They said the process is similar to how a skater's blade reduces friction by melting the ice surface.
"The process allows highly stressed areas to rapidly break down, acting like the weakest links in the chain," said Brown, a professor in the Scripps Geosciences Research Division. "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."
The greater slippage results in stronger earthquakes, according to the scientists. Their experiments were conducted in a laboratory where they Advertisement
Last year's quake off Japan led to a tsunami that ravaged certain coastal areas of northern Honshu and damaged harbors across the Pacific Ocean in California.
"This may be relevant for how you get from large earthquakes to giant earthquakes," Brown said. "We thought that large patches of the fault were just creeping along at a constant rate (off Japan), then all of a sudden they were activated and slipped to produce a mega earthquake that produced a giant tsunami."
According to Scripps, the findings also explain why the San Andreas Fault gives off so little heat from friction compared to the magnitude of the temblors it produces. A reduction in friction during a fault's slippage will lower the amount of thermal energy produced, the scientists found.
Their study was supported financially by the National Science Foundation.
Future studies will include investigations about why the weakening occurs, if their findings apply to most or all common fault zone materials, and an attempt to locate weakening areas, according to Scripps.
source : http://www.thevillagenews.com/story/66071/