Just five months ago, experts warned that "the springs on the San Andreas system have been wound very, very tight. And the southern San Andreas fault, in particular, looks like it’s locked, loaded and ready to go." And now, as The LA Times reports, a rapid succession of more than 200 small earthquakes began rupturing near Bombay Beach, at the southern tip of the San Andreas fault, continuing for more than 24 hours.
The temblors were not felt over a very large area, but, as The LA Times continues, they have garnered intense interest — and concern — among seismologists.
It marked only the third time since earthquake sensors were installed there in 1932 that the area had seen such a swarm, and this one had more earthquakes than the events of 2001 and 2009.
The quakes occurred in one of California’s most seismically complex areas. They hit in a seismic zone just south of where the mighty San Andreas fault ends. It is composed of a web of faults that scientists fear could one day wake up the nearby San Andreas from its long slumber.
The San Andreas fault’s southernmost stretch has not ruptured since about 1680 — more than 330 years ago, scientists estimate. And a big earthquake happens on average in this area once every 150 or 200 years, so experts think the region is long overdue for a major quake.
The swarm actually increased the likelihood of a much more major quake in Southern California, at least temporarily.
According to the U.S. Geological Survey, for the seven-day period following Tuesday, the chances of a magnitude-7 or greater earthquake being triggered on the southern San Andreas fault are as high as 1 in 100 and as low as 1 in 3,000. The chances diminish over time.
Experts said it’s important to understand that the chance of the swarm triggering a big one, while small, was real.
“This is close enough to be in that worry zone,” seismologist Lucy Jones said of the location of the earthquake swarm. “It’s a part of California that the seismologists all watch.”