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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.

A long crack splits the sidewalk in Huntington Beach, on top of the Newport-Inglewood fault. (Credit: Allen J. Schaben / Los Angeles Times)

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.

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