Kern County earthquake won’t delay Big One
LOS ANGELES — Does a good-size earthquake help relieve pent-up seismic stress? Does that postpone the day of reckoning when the Big One finally arrives?
That was the question some in California were asking hopefully in the wake of the July 4 magnitude 6.4 earthquake that rattled the region.
You won’t like this answer.
It’s wishful thinking to imagine that, as a rule, earthquakes “relieve” seismic stress, said seismologist Lucy Jones.
In fact, generally speaking, earthquakes actually increase the risk of future quakes.
Here is a primer on earthquakes and seismic stress largely based on past interviews with Jones and other scientists:
Q:
Does an earthquake immediately relieve seismic stress, forestalling a future big quake?
A:
No.
Think about what generally happens after a decent earthquake. Aftershocks. Lots and lots of aftershocks. It’s going on right now in the area around the Fourth of July magnitude 6.4 earthquake in the Mojave Desert, close to Ridgecrest, a town of 29,000 notable for being a pit stop for Mammoth-bound skiers from L.A.
Q:
But couldn’t relieving seismic stress in one part of the state restart the earthquake clock elsewhere, so to speak?
A:
No. Consider: One part of California, west of the San Andreas, is constantly moving northwest, toward Alaska, relative to the other side of the Golden State, which is headed toward Mexico.
These immense forces are what generated the state’s mountains, from the ranges seen in the Los Angeles Basin to the hills lining the ridges of the Bay Area. There’s a reason why earthquake faults are often alongside hills and mountains.
“If you see mountains in California, that means something is moving up those mountains faster than erosion is wearing them down,” Jones said in an interview published last year. “Basically, when you see mountains, think earthquakes in California.”
It’s also the reason why California has been home to lucrative deposits of oil. It’s the reason where there are springs in the desert giving rise to places like Palm Springs.
There is no avoiding, eventually, big earthquakes being unleashed on faults somewhere in this state. We just don’t know exactly when or where it’ll happen. But just as it’s happened before in centuries and millennia past, it will happen again.
Q:
Explain a bit more about why there are quakes in California.
A:
Think about the San Andreas fault. It’s a doozy of a fault — more than 800 miles long. Just the southern San Andreas fault, between Monterey County to close to the Mexican border, is capable of producing a magnitude 8.2 quake.
Relatively speaking, places on the southwest side of the San Andreas fault — such as Los Angeles, San Diego and Santa Barbara — are inching toward Alaska. Places on the other side of the San Andreas, such as Sacramento and the Mojave Desert, are sliding toward Mexico.
But in places along faults such as the San Andreas, the land on both sides of the fault are locked, even as land farther away continues to move. Eventually, the San Andreas — as well as other faults throughout California — will have to rupture to relieve mounting tectonic strain.
“Plate tectonics hasn’t suddenly stopped; it is still pushing Los Angeles toward San Francisco at the same rate your fingers grow — about 1.5 inches each year .... Their motion cannot be stopped any more than we could turn off the sun,” Jones wrote in her recent book, “The Big Ones: How Natural Disasters Have Shaped Us (and What We Can Do About Them).”
The San Andreas is particularly feared because, in some sections, it will move for many feet almost instantaneously. A famous example was during the great 1906 magnitude 7.8 earthquake that destroyed San Francisco; at Point Reyes in Marin County, a fence that intersected the fault was suddenly cut in two, separated on each side by the San Andreas by 18 feet.