Thursday, March 09, 2017

Earthquake on the beach: Scientists think a 7.4 temblor could reach from L.A. to San Diego

The discovery of missing links between earthquake faults shows how a magnitude 7.4 earthquake could rupture in the same temblor underneath Los Angeles, Orange and San Diego counties, a new study finds.

Such an earthquake would be 30 times more powerful than the magnitude 6.4 earthquake that caused the 1933 Long Beach earthquake, which killed 120 people.

But to get to a 7.4, the earthquake would not only have to again rupture the Newport-Inglewood fault in Los Angeles and Orange counties. The temblor would also have to jolt the adjacent Rose Canyon fault system, which runs all the way through downtown San Diego and hasn’t ruptured since roughly 1650.

“These two fault zones are actually one continuous fault zone,” said Valerie Sahakian, the study’s lead author, who wrote it while working on her doctorate at Scripps Institution of Oceanography at UC San Diego. Sahakian is now a research geophysicist with the U.S. Geological Survey.

In the past, scientists reported gaps between the two fault systems of as much as 3 miles apart. But the latest study shows the gaps are actually less than 1¼ miles apart.

“That kind of characterizes it as one continuous fault zone, as opposed to two different, distinct fault systems,” Sahakian said, making it far easier for an earthquake to keep shaking land as it races down a longer fault, widening the seismic reach of the temblor.

There had already been consensus among scientists over the last three decades that the fault systems were actually one, said Caltech seismologist Egill Hauksson, who was not involved with this study. “We now have real evidence that this is the case,” Hauksson said.

The difficulty in proving it was caused by the location of the gap — under the Pacific Ocean between Newport Beach and La Jolla. Drawing a better map meant trying to figure out where the fault was underwater. - Read More, latimes


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