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.

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.

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

here

. 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.

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.

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.