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Seismologists surprised by deep California quakes

New type of weak temblors in upper mantle detected

2:00pm, October 6, 2016
Newport-Inglewood Fault

CURIOUS QUAKES  A dense network of seismometers monitoring the Newport-Inglewood Fault in Southern California detected earthquakes originating from far deeper underground than once thought possible.

Mysterious earthquakes rattle deep beneath Southern California.

The tiny quakes originate from tens of kilometers below ground along the Newport-Inglewood Fault near Long Beach, Calif., seismologists report in the Oct. 7 Science. Rocks at that depth should be too hot and malleable to snag and break — a key mechanism behind earthquakes. Some unknown process must be at play in the roots of the fault that makes this new type of earthquake possible, says study coauthor Asaf Inbal, a seismologist at Caltech.

“This is a wide open question that we don’t have a good answer to,” he says.

The quakes puzzle scientists, but they don’t pose a direct threat, says Yuri Fialko, a geophysicist at the Scripps Institution of Oceanography in La Jolla, Calif. “Luckily for us, they remain small and don’t grow into bigger, potentially damaging events,”

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