On Shaky Ground

What do an apparent spate of recent earthquakes tell us about "The Big One"?

earthquake fault
Mario Tama

Did you feel it? At 3:49 p.m. Pacific time on July 8, 2021—a week ago today—a 6.0-magnitude earthquake hit Little Antelope Valley in Mono County, California, close to the Nevada border and south of Lake Tahoe. The nearest town was tiny Walker, with a population of fewer than 900 people, just four miles away from the quake’s epicenter. Last Thursday’s earthquake was felt as far away as the San Francisco Bay Area and resulted in social media video and news reports that included classic big-earthquake imagery like merchandise falling from shelves and swaying light fixtures.

Luckily, no serious injuries or damage was reported from the tremor and dozens of aftershocks—some as strong as 4.6 magnitude. Even by native-Californian standards, which include acting very blasé about most minor earthquakes while insisting “I felt that,” last week’s rumbler was a scary one.

Boulders, for those who have never experienced an earthquake, don’t usually come tumbling down onto the highway.

California is most synonymous with earthquakes, despite Alaska’s experiencing more of them. Feeling one’s first quake is a Golden State rite of passage, usually because most earthquakes truly aren’t that big of a deal. Small ones occur daily, and a dedicated community of earthquake experts and amateurs track and analyze each of them. They tell us that last week’s earthquake was the fourth significant quake in California during the past month. On June 4, 2021, two 5.9-magnitude earthquakes, 25 minutes apart, were reported off the coast of southern Oregon, about 150 miles from Arcata, California. This prompted concerns that significant back-to-back earthquakes could imply that a bigger quake was imminent. The very next day, many residents across Southern California experienced a solid 5.3-magnitude quake centered in Calipatria in Imperial County and felt as far away as San Diego and western Arizona. That relatively minor quake was followed by over 40 aftershocks.

The question on everyone’s minds: Does this latest data indicate an increase in quakes or presage the big one?

According to some scientists, not necessarily. For example, a pair of rumblers in Los Angeles County last July increased the likelihood of a major Southern California earthquake in the next 12 months by 1 percent.

Yet scientists also continue to warn us that a major California metropolitan area is likely to experience a severe earthquake in the next 30 years. In Los Angeles, the likelihood of a 6.7-magnitude earthquake within the next three decades is 60 percent and a catastrophic 7.5-magnitude quake is 31 percent. In San Francisco, those same likelihoods are 72 percent and 20 percent, respectively. (Wander down the California earthquake probability wormhole here.)

One way each of us can participate in the expansion of quake-based science is to let the United States Geological Survey know when we feel an earthquake. The “Did You Feel It?” service allows citizens to report on the time, location, and circumstances of any earth-shaking experience. The USGS uses this information to create maps showing the extent of a quake, confirms the shaking experience for others, and provides a rapid assessment of the extent of the earthquake.

In the end, the spate of recent tremblers tells us very little (and neither do dogsor weather, earthquake-myth fans), but it does offer an opportunity to make sure we’re as prepared as we can be.

Alta Journal rated several emergency “go bags” and interviewed experts about evacuation plans for both wildfires and earthquakes. Read the article and listen to the podcast to learn the importance of items like prescription medication and eyeglasses, photocopies of passports, and backup sneakers. Above all: keep comfortable, strong shoes near your bed and door.

When a major earthquake strikes California again, and it will, how will you be prepared? Drop a note to letters@altaonline.com and let us know your plan and tips.•

This essay was adapted from the Alta newsletter, delivered every Thursday.
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