California Experienced Back-to-Back Earthquakes. Here’s What To Expect Next.

“This was a very good wakeup call, essentially,” an emergency official said before urging residents to think about preparedness.

California is on edge after a series of major earthquakes rattled the region during the holiday weekend. While damage was relatively minor, hundreds of temblors continue to shake the region and officials urge Californians to rethink  preparedness for the next “big one.”

Here’s what you need to know about aftershocks, how accurately scientists can forecast future earthquakes and how you should plan for natural disasters.

So, what happened?

California was hit by back-to-back earthquakes over the Fourth of July holiday. On Thursday, a 6.4 magnitude quake struck near a small, rural town in Southern California called Ridgecrest, about 150 miles from Los Angeles. The next day, a larger 7.1 magnitude temblor hit the same area and was felt by millions across the region, from Dodger Stadium in Los Angeles down to Mexico and eastward to Las Vegas.

There has been a steady stream of smaller magnitude aftershocks over the weekend, including 297 earthquakes that were magnitude 3 or higher, according to the latest readings from the U.S. Geological Survey.

Was anyone hurt, and how much damage was there?

There have been no reports of any major injuries or deaths, and officials have cast the event as a timely warning for the state. Investigators have found some damage to homes and businesses in Ridgecrest and a nearby town, as well as roads that were cracked by the quakes. But major cities like Los Angeles avoided any major harm.

The quakes were centered around the small town of Ridgecrest, about 150 miles from Los Angeles. There were no major injuries
The quakes were centered around the small town of Ridgecrest, about 150 miles from Los Angeles. There were no major injuries or deaths.

“We’re very lucky there and happy there wasn’t anything worse,” Mark Ghilarducci, director of the California Governor’s Office of Emergency Services, or OES, told The Los Angeles Times.

California Gov. Gavin Newsom (D) has requested a presidential emergency declaration after the event, declaring a state of emergency in the Ridgecrest area. He offered his sympathies to those affected by the quakes, pledging recovery resources to deal with any damage.

“It is a wake-up call for the rest of the state and other parts of the nation, frankly,” Newsom said at a press conference on Saturday.

Residents have reported being on edge following the twin quakes and the aftershocks.

Are more earthquakes or aftershocks expected?

First, scientists cannot perfectly predict the time or place of an earthquake. Rather, seismologists use data and statistical analysis to forecast how likely another earthquake may be, the USGS notes.

The agency’s current forecast notes there’s less than a 1% chance of one or more aftershocks larger than magnitude 7.1 over the next week. Those statistics also say there’s about a 2% chance for a quake of such magnitude over the next year. Initial forecasts were significantly larger, with some seismologists forecasting about a 1 in 10 chance of another big quake, but they decrease over time.

“The number of aftershocks will drop off over time, but a large aftershock can increase the numbers again, temporarily,” the USGS said. “The expected numbers and probabilities of aftershocks have gone down since the previous forecasts for two reasons. First, it is due to the natural and expected decrease in activity as time passes since the mainshock. Second, our observations of this aftershock sequence show that the activity is decreasing slightly more quickly than average for this area.”

Lucy Jones, a seismologist at the California Intestate of Technology sometimes called the “earthquake lady,” also noted on Twitter Sunday that while the number of aftershocks decreases over time, it that doesn’t mean they won’t happen. She wrote that “large, late aftershocks show up in most sequences,” pointing to 1994’s Northridge earthquake. The last aftershock in that sequence took place years later in 1997.

“We’re going to have a magnitude 6, on average, somewhere in Southern California every few years. We’ve actually gone 20 years without one, so we have had the quietest 20 years in the history of Southern California,” Jones told The Associated Press on Sunday. “Geology keeps on moving ... and we should be expecting a higher rate. And when it happens near people, it is going to be a lot worse.”

What can you do to prepare?

California emergency officials have urged residents to update their go-bags and emergency supplies following the quakes, particularly due to the pause in major earthquake activity over the past two decades.

“This was a very good wakeup call, essentially,” Robb Mayberry, a public information officer with California OES, told HuffPost. “If it happened in a more urban area it would’ve been more disastrous. As large as it was, it got some attention.”

Emergency officials are encouraging Californians to update their first-aid kits and go-bags after the earthquakes, dubbing th
Emergency officials are encouraging Californians to update their first-aid kits and go-bags after the earthquakes, dubbing them a wake-up call after a period of relative quiet.

Mayberry pointed to considerations for any supply kit, including keeping a pair of shoes by the bed and adding batteries or phone charges to emergency kits so residents can stay appraised of information during any potential disaster. Los Angeles County has an early warning phone app for such events as well (although it didn’t activate during last week’s quakes, as the impact on the region didn’t meet the threshold).

The Los Angeles Times notes that less than 12% of California residents have insurance policies that cover earthquakes. Interest in such coverage usually spikes following major events before dipping. The outlet reported that at the time of the Northridge earthquake, 33% of Californians had quake insurance. Between 2012 and 2016, that number was less than 11% each year.