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Chance of Major California Quake Has Risen
| published March 12, 2015 |

By Thursday Review staff

 

People in California are no slouches when it comes to earthquakes: on some days there can be as many as a dozen tremors, hundreds in a typical week or month, and thousands in any given year. The majority of these quakes are mild, and cause little damage. California experiences, on average, two to three quakes of moderate size per year—that is to say quakes big enough to cause modest damage to roads, homes, businesses, and infrastructure like power lines and water mains.

Though California is widely assumed to be the U.S. state with the most earthquakes—and the biggest of the quakes—Alaska has far more since it sits atop a larger number of Pacific Rim faults. Alaska, however, has only a tiny fraction of the population of California, and much of the state is remote and uninhabited. This is why geologists worry more about California, where almost any earthquake, or any size anywhere in the state, can affect places where there is infrastructure and where there are people. Lots of people. By some estimates, three quarters of California’s population resides within areas considered at high risk for large earthquakes.

The Golden State has numerous fissures and faults—hundreds, in fact—but the one most commonly associated with earthquakes is the San Andreas Fault, a fracture line between two large geological plates, the North American Plate and the Pacific Plate. These two structures move past one another at a rate of about 1.5 inches a year, according to the California Department of Conservation.

Los Angeles, in the south, is actually moving closer to San Francisco, in the middle-north; indeed, in a few million years the two downtowns will be just a few miles apart...an amusing thought.

Californians, however, worry not about the little quakes and tremors, but the so-called Big One. For most people, that massive quake remains an abstract idea—something only the future citizens of California will have to worry about.

But a new report from the U.S. Geological Survey says that the chances of that devastating large quake arriving in our lifetime has increased, up from less than 5% in the last set of studies, to more than 7%. The report says that the likely culprit of that big quake will be the San Andreas Fault, and most likely the parts of it which run through Southern California.

Geologists worry most not about all those little tremors and quakes, which simply reveal what we already know—that the two plates are grinding against one another, moving in relation to the other’s position. What worries earthquake analysts are the long stretches of time in between the large quakes. Those periods of relative stability shroud the fact that those forces deep underground are still at work, and with each passing year the pressure builds up—especially in those parts of the fault line where the average rate of slippage is pent up or blocked. Once the fault finally decides to move, the forces unleashed can be powerful.

In other words, the longer Californians go without a major earthquake, the worse the next one will be. Tom Jordan, the director of the Southern California Earthquake Center likens the process to winding up a giant spring.

“Tectonic forces are continually tightening the springs of the San Andreas fault system,” he told CBS Los Angeles, “making big quakes inevitable.”

The U.S. Geological Survey says its studies now rate the chances of a major California earthquake—that is a large quake of a magnitude of 8.0 or greater—within the next 30 years at 7%. Its prediction is based on multiple computer models, and the relatively high risk of simultaneous fault line activity throughout California’s complex system of hot spots.

That’s the bad news. The good news, though it may seem proportionally very small, is that the ability to predict quakes has become better, and in the near future it may be possible for residents of California to have as much as a 20 second warning before a major quake shakes the ground. Twenty seconds is not much, but it could be enough to quickly find safety.

California officials tell residents that although there is nothing that can be done to prevent an earthquake, and even under the best circumstances only a few seconds to prepare or react when one is imminent, newer, smarter building and construction codes—for homes, apartments, high rise buildings, highways and bridges, retail locations and malls, even swimming pools—mean that the severity of damage and the instances of injury and death are greatly reduced. Because of the constant danger earthquakes present, California has stricter and more comprehensive rules and guidelines for any new construction when compared to other states.

Related Thursday Review articles:

Huge Reward for Information on L.A. Fire; Thursday Review; January 22, 2015.