During the first week of July 2019, southern California was hit with some of the strongest quakes the Los Angeles area has experienced in the past two decades.
Yup. California is so over it that it’s physically trying to secede.
On July 4, while the POTUS waxed poetic about George Washington’s takeover of the Revolutionary era airports, Californians celebrated America’s birthday by trying to get the hell out of dodge.
At 10:33 am PST, a 6.4 quake hit the Searles Valley in the Mojave Desert. The quake was centered in Ridgecrest, a small town approximately 122 miles east of Los Angeles.
And then July 5 was all, “Hold my beer,” and at 8:19 pm a stronger 7.1 quake hit the region about seven miles away from the earlier quake. This quake was eleven times stronger than the July 4 quake. It was the strongest quake to hit California in twenty years.
And although quakes can produce thousands of smaller aftershocks, it’s rare that they’ll lead to a bigger quake. Because the 6.4 quake was followed by a stronger quake, it earned the title “foreshock.”
This double-whammy-quake-fest left many Angelenos, especially LA transplants, feeling tenuous about the ground beneath their feet. What if the 7.1 was a foreshock for an even bigger quake? What if these quakes lead to the infamous “Big One” along the San Andreas fault?!
But before you begin imagining California ripping apart at its tectonic seams, let me explain why this is improbable.
Whose Fault Is It?
First of all, the Ridgecrest quakes were not caused by a shift in the San Andreas fault, which would be the source of the Big One. The July 5 7.1 quake occurred in the Little Lake fault zone while the 6.4 quake is a bit more complicated involving multiple smaller faults that are part of the Eastern California Shear Zone.
The Eastern California Shear Zone stretches from Palm Springs to the Owens Valley east of the Sierra Nevada. These faults are unique because they are perpendicular to each other.
A natural follow-up question: Could these quakes along other faults trigger a larger San Andreas quake?
More good news! The fault system that caused the Ridgecrest quakes is too far away to trigger a quake along the San Andreas fault, which would be the source of The Big One. The San Andreas fault is 750 miles long and runs much of the length of California. The fault is a place where two tectonic plates touch, the North American and Pacific Plates. This particular fault is 28 million years old and is unique because it’s a fault that is on land rather than under an ocean, so it’s easy for scientists to study.
Oh, and FYI, these plates are sliding along one another so California will not be falling into the ocean. I repeat, California will not be falling into the ocean!
I know, I know, I kind of looked forward to California becoming the new lost city of Atlantis where we’d become a multiracial society of merpeople, but it’s not going to happen. Though San Francisco and LA might be next to each other one day! In, like, 12 million years. Hey, that’ll probably happen before California gets around to building that bullet train!
Here’s some more (kind of) good news. The San Andreas fault can’t have a 10.0 quake. According to Caltech seismologist Dr. Lucy Jones, the San Andreas fault taps out at about an 8.3 quake. That’s still considered a great quake. Yeah, that’s the technical name, “Great Quake.” There are a lot of great things in this world: kittens, warm summer breezes, broken parking meters, apple fritters. Couldn’t scientists have thought of a different name? Right now quakes fall in different classes. They include minor, light, moderate, strong, major, and great. How about minor, light, moderate, major, and screwed. Cause that’s what we’ll all be.
But I digress …
The last technical San Andreas “Big One” California suffered was the 1906 San Francisco quake that practically leveled that gorgeous contact-high of a city.
It was April 18, 1906, 5:12 am. The quake was preceded by a smaller foreshock about twenty-five seconds before the major 7.9 quake that rocked the city for roughly forty-five to sixty seconds. This massive quake was felt as far away as Oregon and all the way south of LA. The death toll was somewhere between 700–3,000 killed in the quake and subsequent fires.
And that wasn’t even a great quake. It was considered a “major quake,” and they still were screwed.
But Wait! There’s More …
After all that good news, here’s some potentially not-so-great news. The Ridgecrest quakes may be too far away to trigger a San Andreas quake, but the quakes and the subsequent aftershocks have been moving toward two potentially dangerous faults: The Owens Valley Fault and the Garlock Fault. Both of these faults are capable of large quakes, over 7.0—nothing to sneeze at.The Owens Valley Fault and the Garlock Fault, like the faults that caused the July quakes, are all part of the Eastern California Shear Zone. They might not get as much fanfare or their own Dwayne “The Rock” Johnson movie, but this region is still capable of doing damage as far away as Los Angeles.
In fact, in 1872 the Owens Valley fault triggered one of the strongest quakes ever recorded in California. The quake’s magnitude was roughly 7.8 or 7.9, and at least twenty-seven people died as a result of this temblor.
One of the strongest quakes in my memory, the 1992 Landers quake, was triggered by a smaller quake that shook Joshua Tree a few months earlier. The April 22 Joshua Tree quake was a respectable 6.1, but that quake was followed by a quake sixty-three times stronger on June 28. This quake was 7.3. A few hours later, another quake of 6.3 hit the Big Bear area.
Scientists are monitoring the aftershocks to the Ridgecrest quakes and their movement toward larger faults just like doctors monitor the spread of infectious diseases through a population. The Ridgequest quakes have spawned 16,000 smaller quakes—essentially quakes begat more quakes. And sure, an earthquake can be a release of pressure, but the movement can put new pressure on other faults, which may trigger more quakes.
I’m All Shook Up
I grew up in Northridge and have somehow been in California for all its large quakes in the past thirty or so years. In fact, my first quake was technically felt in utero on January 1, 1979. It was a 5.1 quake that struck off the coast of Malibu. It was my mom’s real first Californian quake since moving to LA from New Orleans. Apparently it was felt in Pasadena during the Rose Bowl game, where USC defeated Michigan 10–7 (sorry, Wolverine fans).
And even though I now live in Manhattan, I happened to be in town for the Ridgecrest quakes. The July 4 quake was my first quake in about a decade (the last was a 6.1 magnitude quake in Costa Rica while I was at primate field school. I was too busy chasing monkeys to feel it). As soon as I realized I was feeling a quake, I immediately erupted into nervous laughter because I’ve always found earthquakes both terrifying and invigorating. They are nature’s unpredictable roller coasters.
The Ridgecrest quake was long and rolling, and as I walked out my mom’s door onto her front porch, I looked around at her sleepy suburban neighborhood and was laughing again. Not one person on her street had left their house. That is how chill Angelenos are about earthquakes. I saw one man speed walking down the block. I joked that he probably didn’t feel the quake. I was right. He didn’t.
I was with my spare parents, or “sparents,” for the July 5 quake. They also live in the San Fernando Valley. My spare mom had just had knee replacement surgery and so we were just relaxing in their bedroom, and I may or may not have been stoned when the 8:19 quake hit. Their two cats were on the bed and were completely unperturbed as the bed slowly rocked. The third (much younger) cat launched itself at my spare dad and knocked over the jar of peanuts he was holding. For the duration of the quake my spare dad gave calm, cool, and collected commentary. Even as the quake got stronger, he never panicked. He was more upset about the spilled peanuts than the potential aftershocks.
Both of these quakes were reminiscent of the Landers quake in 1992. Like the Ridgecrest quakes, the Landers quake’s epicenter was a fair distance from LA, roughly 100 miles due east. Far away quakes are a lot more enjoyable because you’re getting the ripples and run-off rather than rough rocky jolts.
So, What’s Next for California?
Well, if you live in the Golden State, I suggest you get your earthquake preparedness kits ready. Lots of water, nonperishable food, hand crank radios, flashlights, and solar panel battery packs. Here is a good list compiled by the CDC. And definitely have some sort of emergency plan in place with family and the friends you’d like to keep informed and safe.
And remember to keep calm and science on …