SOUNDING THE ALARM: Once an earthquake warning system detects a strong quake, the alert goes out. In this scenario, when a break of the San Andreas Fault south of the Bay Area creates a strong tremor, those in the most densely populated areas to the north would have more than half a minute to get ready. Image: Illustration by Emily Cooper and Tom Whalen
- 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.
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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.
This article was originally published with the title Seconds Before the Big One.