Biggest California earthquake in decades ruptured on at least 24 faults

Approved – NV


When an earthquake strikes, the instinct of many Californians is to ask: Which fault ruptured — the Newport-Inglewood, the Hayward, the mighty San Andreas?

New research shows that the Ridgecrest earthquakes that began in July ruptured at least two dozen faults. It’s the latest evidence of how small faults can join together to produce a large earthquake, and how those quakes can cover a wider area than expected.

It has only been in recent decades that earthquake scientists have understood how smaller faults in California join together to create a more powerful earthquake.

So instead of earthquake strain being relieved by many magnitude 6 temblors over a number of faults, “you could just do it in one magnitude 7 by having the rupture travel up and jump from one fault to the next,” Hauksson said.

A modest fault that begins to move in a quake can make it easier for a neighboring fault to rupture, Hauksson said. In Ridgecrest, the Fourth of July earthquakes probably kept on hammering strong spots along seismically strained faults until the larger magnitude 7.1 ruptured on July 5, Hauksson said.

The study raises the possibility that past earthquakes actually may have been bigger than previously thought. A prehistoric earthquake currently identified by a rupture of a fault at one site might have produced even more power if scientists haven’t yet discovered other fault segments that ruptured in the same event, the study said.

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