Although they jangled nerves and rattled windows, the two 4.5-magnitude earthquakes that shook Southern California and probably aren't signs of a pending Big One, experts said.
“There is nothing in this sequence, at this point, that tells us we need to be particularly worried,” said Elizabeth Cochran, a geophycist at the U.S. Geological Survey.
The two quakes belonged to a series of about 30 temblors that rattled the region in less than 24 hours.
The quakes could be a doublet, two main shocks accompanied by a series of aftershocks, she said. Or they could be part of a swarm, meaning another 4.0-ish quake could happen. But the chances of another large shaker are only about 2 percent, she added.
Nevertheless, that doesn't mean the rumbling is entirely over.
Southern Californians are in for a series of aftershocks in the days and weeks to come, Cochran said: “We can definitely expect more of these small earthquakes in the magnitude range of 1 or 2."
Researchers can offer fairly specific predictions for the next several days based upon earthquake patterns.
“In the next 24 hours, we can expect around eight earthquakes of a 2.0 magnitude in the region,” said Debi Kilb, a seismologist with the Scripps Institution of Oceanography. “We would expect the largest aftershock to be a 3.5.”
Although it’s natural for people to worry about the "big one" when a series of medium quakes strike, it’s actually very rare that a major earthquake will follow.
Typically, only about 5 percent of earthquake sequences start small and go larger, said Kilb.
Meanwhile, scientists are working to determine which fault is responsible for the latest quakes. For now, they suspect the Whittier fault zone, a particularly active fault that was responsible for a 4.8-magnitude quake back in 2002.