Deep under Pakistan-administered Kashmir, rocks broke, faults slipped, and the earth shook with such violence on 8 October that more than 70 000 people died and more than 3 million were left homeless [see photo, "

How many lives could have been saved in that one event alone if we'd known of the earthquake 10 minutes in advance? An hour? A day?

Currently, predictions are vague at best. By studying historical earthquake records, monitoring the motion of the earth's crust by satellite, and measuring with strain monitors below the earth's surface, researchers can project a high probability of an earthquake in a certain area within about 30 years. But short-term earthquake forecasting just hasn't worked.

Accurate short-term forecasts would save lives and enable businesses to recover sooner. With just a 10-minute warning, trains could move out of tunnels, and people could move to safer parts of buildings or flee unsafe buildings. With an hour's warning, people could shut off the water and gas lines coming into their homes and move to safety. In industry, workers could shut down dangerous processes and back up critical data; those in potentially dangerous positions, such as refinery employees and high-rise construction workers, could evacuate. Local government officials could alert emergency-response personnel and move critical equipment and vehicles outdoors. With a day's warning, people could collect their families and congregate in a safe location, bringing food, water, and fuel with them. Local and state governments could place emergency teams and equipment strategically and evacuate bridges and tunnels.

It seems that earthquakes should be predictable. After all, we can predict hurricanes and floods using detailed satellite imagery and sophisticated computer models. Using advanced Doppler radar, we can even tell minutes ahead of time that a tornado will form.

Accurate earthquake warnings are, at last, within reach. They will come not from the mechanical phenomena—measurements of the movement of the earth's crust—that have been the focus of decades of study, but, rather, from electromagnetic phenomena. And, remarkably, these predictions will come from signals gathered not only at the earth's surface but also far above it, in the ionosphere.

For decades, researchers have detected strange phenomena in the form of odd radio noise and eerie lights in the sky in the weeks, hours, and days preceding earthquakes. But only recently have experts started systematically monitoring those phenomena and correlating them to earthquakes.

A light or glow in the sky sometimes heralds a big earthquake. On 17 January 1995, for example, there were 23 reported sightings in Kobe, Japan, of a white, blue, or orange light extending some 200 meters in the air and spreading 1 to 8 kilometers across the ground. Hours later a 6.9-magnitude earthquake killed more than 5500 people. Sky watchers and geologists have documented similar lights before earthquakes elsewhere in Japan since the 1960s and in Canada in 1988.

Another sign of an impending quake is a disturbance in the ultralow frequency (ULF) radio band—1 hertz and below—noticed in the weeks and more dramatically in the hours before an earthquake. Researchers at Stanford University, in California, documented such signals before the 1989 Loma Prieta quake, which devastated the San Francisco Bay Area, demolishing houses, fracturing freeways, and killing 63 people.

Both the lights and the radio waves appear to be electromagnetic disturbances that happen when crystalline rocks are deformed—or even broken—by the slow grinding of the earth that occurs just before the dramatic slip that is an earthquake. Although a rock in its normal state is, of course, an insulator, this cracking creates tremendous electric currents in the ground, which travel to the surface and into the air.

The details of how the current is generated remain something of a mystery. One theory is that the deformation of the rock destabilizes its atoms, freeing a flood of electrons from their atomic bonds, and creating positively charged electron deficiencies, or holes.

One of us, Freund, working at NASA Ames Research Center in Mountain View, Calif., demonstrated through laboratory rock-crushing experiments that the sundering of oxygen-to-oxygen bonds in the minerals of a fracturing rock could produce holes. These holes manage to propagate through rock up toward the surface, while the electrons flow down into Earth's hot mantle. The movement of these charges, measured at 300 meters per second in the lab, causes changes in the rock's magnetic field that propagate to the surface.

Another theory is that the fracture of rock allows ionized groundwater thousands of meters below the surface to move into the cracks. The flow of this ionized water lowers the resistance of the rock, creating an efficient pathway for an electric current. However, some researchers doubt that water can migrate quickly enough into the rock to create large enough currents; for this theory to be correct, the water would have to move hundreds of meters per second.

Whatever the cause, the currents generated alter the magnetic field surrounding the earthquake zone. Because the frequencies of these magnetic field changes are so low—with wavelengths of about 30 000 kilometers—they can easily penetrate kilometers of solid rock and be detected at the surface. Signals at frequencies above a few hertz, by contrast, would rapidly be attenuated by the ground and lost.

We can detect such electromagnetic effects in a number of ways "