Seconds before the big one

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.