Scientists discover evidence of super-fast, 'sonic boom' earthquake deep within the Earth

Courtesy: NOAA

Tuesday, July 15, 2014, 4:18 PM - Scientists at the Scripps Institute of Oceanography have found evidence of a super-fast earthquake occurring hundreds of kilometres below the Earth's surface.

It's the first evidence that deep earthquakes -- i.e., ones that form more than 400 kilometres below the surface -- can rupture faster than shallow quakes.

A 'supershear' earthquake occurs at break-neck speeds of up to 14,484 kilometres per hour, causing an effect similar to a sonic boom. Until the Scripps study, scientists had only observed the phenomenon at shallower depths.

In a paper published earlier this month, researchers say they discovered the first deep supershear quake while investigating the aftershocks of a magnitude 8.3 quake that occurred on May 24, 2013 off the Russian mainland. The team was intrigued by a magnitude 6.7 aftershock which ruptured 640 km below the surface at an extraordinary pace.

"For a 6.7 earthquake you would expect a duration of seven to eight seconds, but this one lasted just two seconds," said Peter Shearer, a geophysicist at Scripps, in a statement.

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“This is the first definitive example of supershear rupture for a deep earthquake since previously supershear ruptures have been documented only for shallow earthquakes.”  Scripps says the discovery could shed some light on how deep -- and shallow -- earthquakes rupture.

“This finding will help us understand why deep earthquakes happen,” said Zhongwen Zhan, another geophysicist at Scripps, in a statement.

“One quarter of earthquakes occur at large depths, and some of these can be pretty big, but we still don’t understand why they happen. So this earthquake provides a new observation for deep earthquakes and high-rupture speeds.”

The complete study can be found in the journal Science.

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