Quasar emissions used in earthquake study

Press, Volume CXIV, Issue 33693, 16 November 1974, Page 22

Quasar emissions used in earthquake study

(By

WALTER SULLIVAN,

of the "New York TimesC through N.Z.P.A.)

Radio emissions from objects billions of light years away are being used in an effort to record — in fractions of an inch — the kind of warping of the California landscape that is believed to precede major earthquakes.

It is hoped that the emissions, from the most distant objects known, called quasars, will provide a method of earthquake prediction not available from other measurements, which reveal only changes in horizontal distance between landmarks.

About 20 quasars are being used as “benchmarks in the sky” to watch for changes in the locations of benchmarks

in the earthquake-prone terrain of California. It is now widely believed that a swelling of the landscape occurs before major quakes. Qusars are being used because, in view of their extreme distance from earth, their positions relative to one another within the framework of the sky remain unchanged. Closer sources of radio emission tend to move in that respect. While the nature of quasars is uncertain, many suspect they are the cores of great star systems or galaxies “burning'’ so brilliant, both in terms of light and radio waves, that they can be observed billions of light years away. That is, their light has required billions of years to reach the earth. While the quasar emissions are irregular, the relative arrival times of any particular wave front at two widely spaced antennas can be determined by a method known as interferometry. To this end, extremely precise time recordings are essential and the California measurements depend on clocks accurate to one ten-billionth of a second.

It is as though the random radio signals from a quasar were the sounds of a distant gunfight and the arrival times of each’ gunshot were being monitored at two antennas. The lag in the arrival time at one antenna, relative to the other one, would indicate how much farther away it was from the gunfight.

If, then, a warping of the landscape altered this time lag. the change could be taken as indicative of an impending quake.

A number of quasars in different parts of the sky are being used to develop threedimensional data on the benchmark locations. One of the antennas, 30ft in diameter, is movable and is being shifted to a variety of sites.

In this way, measurements can be made across the various faults where earth movements have produced damaging earthquakes in southern California. The most devastating is the San Andreas Fault. According to Peter F.

MacDoran, who is leading the project at the Jet Propulsion Laboratory in Pasadena, California, the fault will be spanned by several observation baselines. It was on that fault, at Fort Tejon north of Los Angeles, that the worst earthquake ever reported in the West Coast of the United States occurred, in 1857.

To check the reliability of the technique, one baseline has been chosen where no changes are expected. It extends from Goldstone, site of the fixed antenna in the experiment, to southern Nevada. The Goldstone “dish,” 210 feet in diameter, is the main antenna of the Jet Propulsion Laboratory’s space tracking system. N.A.S.A. LABORATORY

The laboratory is operated for the National Aeronautics and Space Administration by the California Institute of Technology. Mr MacDoran, in a telephone interview said that in recent days about nine hours of quasar recording had been done by the portable and fixed antennae. The immediate goal, is a measurement accuracy of about four inches, with the expectation that, in a few years, the margin of error will be less than one inch. Some now believe, Mr MacDoran said, that the region within several miles of an impending earthquake site swells as much as several feet before the event but

measurement of such an effect in the past has been close to impossible.

It is planned to make measurements along each baseline at least once a year The technique, known as ARIES (for Astronomical Radio Interferometric Earth Surveying), depends on instruments initially designed for space exploration.