August 30, 2012

Scientists Identify Hot Spots That Trigger Earthquakes

Lee Rannals for redOrbit.com — Your Universe Online

Scientists are reviving a century old Tesla experiment by trying to recreate an earthquake through laboratory means.

Nikola Tesla tried recreating earthquakes with his electro-mechanical oscillator, or "earthquake machine," back in 1898. He attached the device to building structures in a laboratory on Houston Street in New York.

According to legend, the machine shook not only his building, but neighboring structures, leading police to come to his doorstep and make him shut it off.

Now, scientists at Scripps Institution of Oceanography at University of California, San Diego have created a device to help them better understand earthquakes.

While Tesla's device was to aimed at trying to create quakes, the modern researchers wanted to discover how fault zones weaken in select locations after an earthquake reaches a tipping point.

The scientists reported in the journal Nature they have found new information through their laboratory experiments mimicking earthquake processes that show just how these faults weaken.

They said "melt welts" are the culprit on how fault zones weaken in particular locations.

"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," Kevin Brown, first author of the study, said in a statement.

"The process allows highly stressed areas to rapidly break down, acting like the weakest links in the chain. 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."

Yuri Fialko, a paper coauthor, said the findings add to the understanding of the earthquake process. He said they address the questions of how these ruptures become energetic and dynamic.

Faults zones like the San Andreas Fault produce very little heat from friction when considering the size and magnitude of the earthquakes they produce.

Laboratory experiments have shown that thermal energy released by friction during slip can become rapidly reduced, which could potentially help account for a "low heat flow paradox." The melt welts could also explain questions in earthquake rupture dynamics, such as why some slowly slipping tremor-generating events can snowball into massive earthquakes if they pass a velocity tipping point.

"This may be relevant for how you get from large earthquakes to giant earthquakes," Brown, who used the example of last year's magnitude 9.0 earthquake off Japan, said in a press release. "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."

Fialko said their finding could eventually lead to improved "shake" maps of ground-shaking intensities, and also lead to improved structural engineering plans.

Further research could be done to look into why the melt welt weakening occurs, and in what areas.