An earthquake and dozens of aftershocks rattled Southern Californians starting on Tuesday night and continuing into Wednesday morning. Could a bigger one be on the way?
As a general rule, the risk is fairly low. About 5% to 10% of all California earthquakes are followed by a larger one within a week, and the probability of a larger quake depends on how much aftershock activity there is, according to the USGS. Lots of aftershock activity doesn't guarantee a bigger quake, however.
This latest quake certainly has aftershock activity. A magnitude 5.2 quake at 9:09 p.m. in Lamont near Bakersfield was felt as far away as Los Angeles, over 100 miles from the epicenter. Since then, the U.S. Geological Survey has recorded dozens of aftershocks ranging from 2.5 to 4.5 in magnitude, none as large as the initial quake.
Tuesday's earthquake is the most recent shaker to hit California. On Aug. 2, a3.3-magnitude earthquakecentered on the west side of the Salton Sea was felt in parts of Southern California. On July 29, a 4.9-magnitude earthquake centered 14 miles northeast of Barstow rattled the high desert and parts of Southern California.
Can earthquakes be forecast?
Experts say there's no real way to tell whether a large quake will be followed by something bigger until after it happens.
"We have never found any characteristic that makes a quake more likely to be a foreshock," said seismologist Lucy Jones in a social media post.
There isn't a known fault in the area where the earthquake struck on Tuesday night, but it's still an area known for earthquakes, said Ole Kaven, U.S. Geological Survey research geophysicist.
As time goes on, the chances of a bigger quake go down, but the swarm of aftershocks does raise some eyebrows.
"Because of the productive nature of the aftershock sequence, the chance of another shock 5.0 or greater is a slightly higher," Kaven said. "It’san interesting event in a place you don’t normally expect it, but it is certainly earthquake country so we need to be prepared for the possibility."
What is an aftershock? A foreshock?
When an earthquake is followed by one or more quakes smaller in size in the same area, the later quakes are called aftershocks.
But when an earthquake is followed by a larger one, the first quake becomes known as a foreshock.
One last term: The largest quake in a sequence is the mainshock.
Complicating matters: It's not fully possible to identity a mainshock until after the fact — you have to wait to see if a larger quake comes.
Have large foreshocks happened in California before?
About half of California's biggest earthquakes in history have been preceded by foreshocks. California's increased seismic activity compared to elsewhere in the U.S. makes it more likely for large quakes to occur in sequence, but the relative rarity of large earthquakes still makes it unlikely.
A sequence of small quakes that began rattling the morning of July 4, 2019, became foreshocks to two of the state's largest earthquakes in two decades, according to scientists at Stanford. Later that morning, a 6.4 near Ridgecrest, California, prompted evacuations and caused fires to break out. The next day, a 7.1 earthquake struck the same area.
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Research into one of California's largest earthquakes in history, the 1857 Fort Tejon quake, which hit with a magnitude of about 7.9, shows that in the hours leading up to the mainshock, there were at least two widely felt foreshocks of between a 5 and 6 magnitude.
San Francisco's catastrophic 1906 earthquake came roughly 20-25 seconds after a foreshock was felt throughout the city.
When will 'The Big One' hit?
The infamous but elusive possibility of a devastatingly large earthquake known as "The Big One" always comes to mind when a significant quake strikes in California.
But there's actually several devastating quakes that will eventually hit the state.
The USGS estimates that within the next three decades, there's about a 46% chance an earthquake of magnitude 7 will hit in the Los Angeles area, and a 51% chance it will happen in the Bay Area.
The chances of a 7.5 magnitude quake are 31% in the Los Angeles area and 20% in the San Francisco area in the next 30 years.
What am I supposed to do during an earthquake?
It depends on where you are at.
Here’s what to do in the following situations, according toReady.gov:
- Turn face down and cover your head and neck with a pillow if you’re in bed.
- If you are outside, stay outdoors and away from buildings.
- If you are inside, stay. Avoid doorways and do not run outside.
To protect yourself during an earthquake, drop down to your hands and knees and hold onto something sturdy. Cover your head and neck with your arms and crawl underneath a sturdy table or desk to shelter. If that’s not available to you, then crawl next to an interior wall to get away from windows. If you are under a table or desk, hold onto it with one hand so that if it moves, you can move with it.
