Quakes and Quasars

Except to fuel arguments among astronomers, quasars (for quasi-stellar objects) have proved of no practical value since their discovery in 1960. Now the faint, far-off points of light that are possibly the most distant objects in the universe--up to 12 billion light-years away --promise to take on more earthly importance. Scientists at Caltech's Jet Propulsion Laboratory are hoping to use the bursts of high-frequency radio energy that come from quasars to help them predict earthquakes.

In theory, such forecasting should be easy. All tremors are preceded by small movements in the earth's crust. As these shifts occur, usually along existing faults in the crust, they cause a gradual buildup of stresses and strains that must eventually be released, sometimes violently.

If scientists could accurately measure those early earth movements, they could probably foretell when and where a quake will strike. Unfortunately, the pretremor movements are so slight that not even sophisticated devices using lasers will always work.

J.P.L. scientists are trying a different technique: they tune in to the signals from the same quasar with two different antennas located many miles apart. Because of their separation, one antenna will pick up the signal slightly ahead of the other. The time difference is infinitesimally small--perhaps only a ten-billionth of a second. Yet it can be measured with the help of atomic clocks and computers. Once the difference in the signal's arrival time is known, the distance between the two antennas as well as their elevation can be calculated with an accuracy of an inch, or even less.* If subsequent measurements months or years later reveal changes in the established distance between the antennas or their altitudes, it will be a sure sign of movement in the earth's crust.

Across San Andreas. Called Project ARIES (for Astronomical Radio Interferometric Earth Surveying), the experiment began last month using NASA'S 210-ft. dish antenna in California's Mojave Desert and a portable 30-ft. antenna at J.P.L.'s home in Pasadena. About 125 miles apart, the antennas formed a direct line across the San Andreas fault, source of California's most devastating quakes. But in coming months the smaller antenna will take to the road and make measurements across other quake-prone terrain. The scientists will bring their equipment back to each site at least once a year in an effort to accumulate such an extensive record that they will be able to tell exactly how the earth's crust is moving--and thus get a fix on future earthquakes.

* The technique can only work with radio sources like quasars that are so far off that their movements in space do not effectively change their relative distance from each antenna. The closer stars in the Milky Way cannot be used because their movements around the galaxy would upset the measurements on earth.

This file is automatically generated by a robot program, so viewer discretion is required.