Earthquake!

more When red granite is subjected to extreme crushing pressures in the laboratory, as in this experiment conducted by Freund and colleagues, its surface emits infrared radiation.

Electrical currents in rock might explain another curious observation: Scientists doing research with magnetometers just before major earthquakes have serendipitously recorded tiny, slow fluctuations in Earth's magnetic field. One example happened during the Loma-Prieta earthquake that devastated San Francisco in 1989. Almost 2 weeks before the quake, readings of low-frequency magnetic signals (0.01-0.02 Hz) jumped up to 20 times above normal levels, and then spiked even higher the day of the quake.

The cause of these signals is unknown. In addition to Freund's idea, theories include the movement of deep, ion-conducting groundwater into cracks opened up by the crushing of rocks, electromagnetic energy released by electrons that are sheered from crystalline rocks such as granite, and a piezo-magnetic effect triggered by pressure applied to certain kinds of rocks.

A company called QuakeFinder is hoping that these faint magnetic signals (typically less than 1 nanotesla) can be detected by a satellite in low-Earth orbit. Ground-based sensors can detect these fluctuations as well, but polar-orbiting satellites have the advantage of covering most of the Earth's surface each day.

On June 30, 2003, Quakefinder launched QuakeSat. Measuring only 4 in. x 4 in. x 12 in., the satellite will operate for a year to see whether it can sift out magnetic signals generated by tectonic activity. The first six months of the mission will be spent calibrating the satellite and gathering baseline data. After that ground controllers will be looking in earnest for quakes.

Both the infrared and magnetic methods of quake detection are controversial. For now InSAR seems to be a safer bet for earthquake forecasting. All three, however, offer a tantalizing possibility: Someday the local weather report will forecast not only of the storms above us, but also the ones brewing beneath our feet.

More information:

Watch 'When Nature Strikes Back: Earthquakes' TV Documentary here

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