- Earthquake early-warning networks detect the earliest stages of an earthquake and sound an alarm to warn people of the danger. The alerts can provide tens of seconds of warning time.
- Most systems rely on the fact that an earthquake comes in two parts: a fast-moving, sudden jolt and a slower-moving wave that causes the great majority of the damage.
- A network of seismometers can quickly identify the earthquake’s epicenter, improve predictions of the earthquake’s magnitude and reduce the incidence of false alarms.
- These networks already exist in a number of countries around the world. A proposed system for California would protect individuals and businesses up and down the Golden State.
Editor's note (3/11/11): This article is from the forthcoming April issue of Scientific American. We are posting the text of the article early in light of the deadly Japan earthquake and resulting tsunami.
Earthquakes are unique in the pantheon of natural disasters in that they provide no warning at all before they strike. Consider the case of the Loma Prieta quake, which hit the San Francisco Bay Area on October 17, 1989, just as warm-ups were getting under way for the evening’s World Series game between the San Francisco Giants and the Oakland A’s. At 5:04 p.m., a sudden slip of the San Andreas Fault shook the region with enough force to collapse a 1.5-mile section of a double-decker freeway and sections of the Bay Bridge connecting Oakland with San Francisco. More than 60 people died.
Over the years scientists have hunted for some signal—a precursory sign, however faint—that would allow forecasters to pinpoint exactly where and when the big ones will hit, something that would put people out of harm’s way. After decades spent searching in vain, many seismologists now doubt whether such a signal even exists.
Yet not all hope is lost. Within seconds of an earthquake’s first subtle motions, scientists can now predict with some certainty how strong and widespread the shaking will be. By integrating new science with modern communications technologies, the authorities could get a few tens of seconds’ warning, perhaps even half a minute, to those in harm’s way. That may not sound like much, but it is enough to send shutdown warnings to power plants and rail networks, automatically open elevator doors and alert firefighters.
The Loma Prieta quake was centered south of the Bay in the rugged Santa Cruz Mountains. After the ground started to shake, it took more than 30 seconds for the damaging vibrations to travel the 60 miles to San Francisco and Oakland, the scenes of more than 80 percent of the fatalities. If an earthquake early-warning system had existed back then, it could have provided perhaps a 20-second warning to the heart of the region. This is enough time to slow and stop trains, issue “go around” commands to airplanes on final approach and turn streetlights red—preventing cars from entering hazardous structures such as bridges and tunnels. Workers in hazardous work environments could move to safe zones, and sensitive equipment could enter a hold mode, reducing damage and loss. Schoolchildren and office workers could get under desks before the shaking arrived. The region would be ready to ride out the violence to come.
Such networks are being deployed all over the world in locations as diverse as Mexico, Taiwan, Turkey and Romania. Japan’s system is among the most advanced. The nationwide network issues warnings via most television and radio stations, several cell phone providers, and the public address system of malls and other public spaces. In the three and a half years since the system came online, more than a dozen earthquakes have already triggered widespread alerts. People in factories, schools, trains and automobiles were given a few precious moments to prepare; following the alerts, there were no reports of panic or highway accidents. The U.S. is behind the rest of the world, but a new test bed being deployed in California should soon lead to a full-scale warning system in that fault-ridden state.
California is long past due for the next big one. If we build a warning system now, we can save lives.
From Waves to Warnings
The ground beneath our feet is moving. As the tectonic plates drift across the earth’s surface, pieces of the continents grind past one another and collide like cars in a freeway pileup. The earth’s crust—the outer layer of the plates that we live on—is elastic, but only to a point. At the plate boundaries, the crust bends until the strain becomes too great. When it snaps, the energy stored up over the preceding decades tears across the earth’s surface, shaking everything in its path.