Do the recent quakes tell us anything about the big one?

A couple of big earthquakes interrupted the Independence Day weekend. The epicenter of the 6.4 and 7.1 magnitude quakes was in Ridgecrest, about 100 miles from the San Andreas fault. Now people are wondering what this means for the giant quake that experts predict will strike at any time.

James Dolan, earthquake geologist and professor of Earth Sciences at USC, was in Ridgecrest over the weekend. 

He's particularly concerned about the relationship between the 7.1 quake and the Garlock fault, which is near Frazier Park and extends 150 miles eastward to Death Valley. It also intersects with the San Andreas fault. 

He says the Garlock is probably the biggest fault in Southern California that isn't on people's radars because it's never produced a historic quake. He says the last quake on the Garlock was 7.5-7.7 magnitude. 

"The concern is all these faults are interrelated. Earthquakes occur in response to stress down inside the Earth's crust. And the earthquake itself on any specific fault relieves the stress locally at that fault. But the stress doesn't go away. It just gets redistributed to all the other faults, and it brings some of them closer to failure, and it moves some of them further away from failure," he explains. "So the worry here is that it appears to have moved the Garlock a little closer to failure… We've had a fault that's sitting there for 500 years without a big earthquake that got unclamped." 

Dolan says if there's a Garlock fault quake, it might trigger a San Andreas fault quake, and the weekend's 7.1 magnitude quake already unclamped the Garlock fault. 

He says it's inevitable that the San Andreas fault will be triggered, and what matters is not when it occurs, but what will happen, and it's all about "armoring our infrastructure," including water lines. 

--Written by Amy Ta, produced by Rosalie Atkinson



  • James Dolan - earthquake geologist and professor of Earth Sciences at USC