Explainer: 8.7 ideas in earthquake prediction
Earthquakes are notoriously difficult, if not impossible, to predict. "You are dealing with a very complex physical system that behaves very differently in many places," says David Schwartz, a geologist with the U.S. Geological Survey's San Francisco Bay Area Earthquake Hazards Project. Seismologist Andy Michael, with the agency's Western Earthquake Hazards Team, says some earthquakes may rupture without any early warning signs, rendering the science of earthquake prediction futile. Nevertheless, researchers are trying to improve earthquake probability forecasts and working toward, maybe one day, prediction and prevention. Click the "Next" arrow above to learn about eight of their ideas.
Probability forecasts, state-of-the-art
The color-coded map of California shown here is an example of the state-of-the-art in earthquake forecasting. Areas shaded red have the highest probability an earthquake will occur within the next 30 years. The forecasts are generated from scientific data on factors such as how the faults move and the average time between big temblors. It provides information that planners, engineers and response people can use to make decisions, Schwartz says. The assessment behind this graphic found a 99.7 percent chance a magnitude 6.7 quake or larger will strike California by the year 2037.
Are rumblings a harbinger of looming disaster?
In 1989, two months before the magnitude 7.1 Loma Prieta earthquake rocked the Bay Area in northern California, seismic activity increased to eight times normal levels in regions adjacent to the fault that ruptured. In retrospect, researchers noticed similar patterns prior to major temblors elsewhere in California. And in 2002, a magnitude 6.7 earthquake struck a week before a magnitude 7.9 quake on a section of the Denali Fault that hadn't ruptured for some 450 years. "There is an appreciation that some of these moderate events could be an indication that a fault system is beginning to reach some sort of failure," Schwartz says. "But you can't quantify it any more than that."
First earthquake waves may provide early warning
Earthquakes send out two main types of waves — P and S — and key differences in how quickly they travel could buy people a few seconds to take action, such as crawling under a desk or shutting off a gas line. Some scientists believe the faster-moving Ps, or pressure, waves contain information about the slower-moving but more damaging S's, or secondary, waves. Sensors set up to detect the P's can sound alarms warning of the S's to come. "The key there is observing an earthquake has happened and telling how big it is very quickly and, I think, there is still some legitimate debate about how accurately one can do that," says seismologist Michael. Nevertheless, the USGS is keeping its eyes on a system deployed in Japan where a 6.8 magnitude earthquake in 2007 damaged this road leading to the world's largest nuclear power plant.
Aftershock forecasts posted online
When a major earthquake strikes, residents should brace themselves for aftershocks. But when and where will they occur? California residents can go online to get a 24-hour aftershock forecast such as the one shown
. It uses a color code to indicate the probability that any given area of the state will experience shaking strong enough to knock objects off a table. The forecast is updated hourly. Blue areas have about a one in a million chance of such an aftershock. Red areas are a less than one in 10 chance.
Crustal deformation studied for signs of pending quakes
Does the earth's crust deform prior to a major earthquake? "I would have to put that under a hypothesis at this point," says Michael. "And I think the evidence, so far, is against it." But researchers are using satellites and GPS receivers in the hopes they'll detect a change in the earth's surface in the days, weeks, or months before a major earthquake. One effort, called the Plate Boundary Observatory, has installed several hundred GPS recorders, such as this one near Mt. Hood, Ore., throughout the western U.S. to monitor crustal strain. Another effort called InSAR (Interferomatetric Satellite Aperture Radar) monitors millimeter-scale ground movements from space. If the technique is proven successful, Schwartz says it might provide a bridge between "decades-long forecasts and instantaneous prediction."
Can animals predict earthquakes?
Cal Orey, a California-based author and journalist shown here with her dog Simon, is one of many people who believe their pets pick up on some sort of cues that an earthquake is imminent and start to act strangely. Most seismologists who have looked into the issue, however, have found nothing tangible to support the notion. Schwartz says he's heard plenty of anecdotes, however, and can't 100 percent rule out the possibility. "If there is something there, we just don't know how to get our hands around it," he says.
Can earthquakes be safely triggered?
Some scientists suspect water pressure from the reservoir behind the dam in the background of this image triggered the May 2008 magnitude 7.9 earthquake in Sichuan Province, China. Dam reservoirs have triggered other, smaller earthquakes, including a 6.4 earthquake in India in 1967. As well, waste fluids pumped into a well at the Rocky Mountain Arsenal in Colorado triggered a series of quakes in the 1960s. Given that humans have accidentally triggered quakes, could they intentionally trigger a quake, too, perhaps in hopes of preventing a larger quake from striking in the future? "There's a pretty high liability associated with fooling around like that," Schwartz says. Nor is anyone trying to do it, Michael adds.
Get prepared, then live life
With no way to prevent earthquakes and scant hope scientists will be able to reliably forecast earthquake activity beyond probabilities parsed in decades, the best steps people can take today is to prepare for the big one and then get on with life. That means making sure buildings and bridges and pipelines are built to code to withstand the violent shaking from a worst-case scenario earthquake, such as 1989 Loma Prieta quake shown here. "If you get people prepared, they can honestly put it out of their minds because when it happens — or if it happens — they'll be ready for it," Schwartz says. Many experts say cities have lots of preparation left to do.
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