Magazine article Science News

Cracking Open the Center of a Temblor

Magazine article Science News

Cracking Open the Center of a Temblor

Article excerpt

Cracking open the center of a temblor

Like expectant fathers of yesteryear, confined to pacing in the waiting room, seismologists cannot actually witness the birth of an earthquake. Instead, they must rely on information gathered by listening devices placed on the ground surface, far from where the action occurs.

Despite this handicap, a new generation of instruments monitoring northern California's Loma Prieta quake has given researchers their best glimpse yet of a fault beginning to rupture.

The instruments, called broadband seismometers, can record both long- and short-period waves created by earthquakes. Unlike other monitoring devices, which become overwhelmed almost instantly by intense shaking, they can continue to record seismic waves when a quake hits nearby. California scientists have deployed these seismometers for several years, but the Loma Prieta temblor of October 1989 was the first large quake to hit an area equipped with them.

The devices that recorded Loma Prieta are among the simpler broadband instruments available today, and they caught only the first few seconds of the seismic waves before succumbing to the shaking. But even that short span of data has provided unprecedented information, says David Wald of the California Institute of Technology in Pasadena. He and his colleagues presented their findings in San Francisco this week at a meeting of the Seismological Society of America.

The researchers report that Loma Prieta started with a perplexing prologue of weak, long-period vibrations. …

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