Early Warning

About 12 seconds before the October 17 earthquake shook the San Francisco and Oakland region, 10 sensors placed along the Bay Area Rapid Transit’s subsurface rail lines warned of the imminent tragedy. Detecting the harmless “P waves” that arrived from the earthquake’s epicenter shortly before the more destructive “S waves,” the sensors triggered an alarm system that brought the trains to a crawl until they reached their next stations. The sensors are part of a burgeoning earthquake detection industry, of which Earthquake Safety Systems Inc., of Van Nuys, Calif., is but a part. The company placed its BART sensors in the subway tunnels years ago; it has gone on to install sensors and automatic shutdown systems in schools, public auditoriums, and factories.

According to Owen Widdicombe, the firm’s president, such “specific-site” instruments are more practical than trying to detect earthquakes as they happen on the fault lines. “Local...

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