Is California Due for a Big Earthquake?

  • The San Andreas Fault

    The 9.3-mile deep San Andreas Fault in California is one of the longest and most active in the world. This computer-generated image is enhanced to show its features.SRTM, JPL, NASA

  • California Earthquake Probability Map

    The colors on this map of California represent the probability of a nearby earthquake rupture (within 3 or 4 miles) of magnitude 6.7 or larger in the next 30 years. The chance of such an event exceeds 99 percent.SCEC/USGS/CGS

Small earthquakes in California ... tremors near the Philippines ... devastation in Haiti. Is the Earth in a period of increased seismic activity? And is the U.S. due for a big one?

A handful of quakes have shaken California over the past few weeks, ranging from smaller 4.4-magnitude shakers to a larger (and more recent) 6.5 quake off the Northern coast of the state. Californians have long lived uneasily in the presence of the San Andreas fault, the massive rift that runs the length of the state. But in light of the recent rumblings there and the dreadfully destructive quake in Haiti, many are worrying that the long-feared "Big One" on the West Coast may be just around the corner.

"Earthquake prediction has been something of a Holy Grail for the seismological community, and has proven just as elusive," says David Bowman, chairman of the department of geological sciences at California State University, Fullerton.

Every year there are approximately 150 earthquakes greater than magnitude 6, and 15-20 events above magnitude 7 somewhere in the world, Bowman said in an interview. Some can be as deep as 500 miles beneath the surface of the earth, and they are barely noticeable. 

But the 7.0 earthquake in Haiti this week was not only strong, it was also quite shallow -- just six miles underground, a factor that increased its destructive power. The quake's center was a few miles southwest of the well-populated capital, Port-au-Prince, which is along a 60-mile stretch of the Enriquillo-Plantain Garden Fault. That fault line runs east-west and reaches as far as Jamaica.

A shifting tectonic plate -- massive segments of the Earth's crust -- lies just south of Haiti. The Caribbean Plate slowly slides eastward. Further north, the North American Plate moves in the opposite direction. Stress builds up slowly as the two plates grind along a mutual boundary, and it is released through small temblors or via a major earthquake. The shift under Haiti came in a horizontal, side-to-side motion.

It was Haiti's first earthquake in a century.

But while the geological events behind the Haitian earthquake are somewhat startling, it is highly unlikely that the temblor had anything to do with the recent seismic events in California, or that it presages another pending disaster elsewhere, scientists say.

"The rate of earthquakes is more-or-less constant on a global scale," Bowman told "However, as the Earth's population continues to grow and as our societies become ever more linked through communication and commerce, our awareness of individual earthquakes has grown.

"There is no known connection between these events," he said. "The fact that these earthquakes happened so closely together in time is a coincidence. To draw an analogy, USC, my alma mater, won the 2004 BCS Championship in Football, and Cal State Fullerton, my employer, won the 2004 College World Series. Is there some connection between them? No."

Nevertheless, scientists believe a tremendous earthquake in California is almost inevitable. In 2008, a multi-disciplinary collaboration of scientists and engineers released the Uniform California Earthquake Rupture Forecast (UCERF), which predicts a 99.7 percent likelihood of a 6.7 or larger earthquake in California in the next 30 years.

Other disasters may be in store for Americans as well, notably the so-called "supervolcano" beneath Yellowstone National Park

"This is an active volcanic and tectonic area, and these are the kinds of things we have to pay attention to," said Robert Smith, who directs the Yellowstone Seismic Network, which operates seismic stations around the park. He said quakes in the park have ranged in strength from barely detectable to one of magnitude 3.8 that happened last year.  

"Could it develop into a bigger fault or something related to hydrothermal activity? We don't know. That's what we're there to do, to monitor it for public safety."

Lubos Motl, a Czech theoretical physicist, and former Harvard University assistant professor, said a particular earthquake can be predicted only "a few seconds" before it begins. "Earthquakes are really fast, and pretty much random, geological events," he said, adding: "It's somewhat unlikely that our ability to forecast earthquakes will increase significantly when the technology gets better." 

Keith Lockitch, a fellow at the Ayn Rand Institute in New York City, said Haiti, the most impoverished nation in the Western Hemisphere, suffered terribly because its economy makes it much less resilient to disasters like earthquakes and hurricanes.

"The toll of death and human suffering is much worse in a pre-industrial country like Haiti than it would be from a comparable quake near, say, San Diego," Lockitch said. "What the tragedy in Haiti should make us realize is just how important industrial development under capitalism is in keeping people as safe as possible from such events."

Others advise caution in overestimating the scientific importance of the Haiti earthquake, even though TV imagery demonstrates the great human tragedy. "In the scheme of things, neither of the earthquakes was really that big," says Susan Hough, a seismologist at the U.S. Geological Survey, Pasedena, Calif., and author of Predicting the Unpredictable: The Tumultuous Science of Earthquake Prediction. Regarding the quakes in Haiti and Northern California, she pointed out, "What's notable of the recent events is that both struck close to where people live."