New Detection Hope

Five months ago, U.S. negotiators struggling to achieve an agreement with the Russian scientists on a detection system for atomic explosions were thrown into confusion. Tests had shown that underground explosions could not be detected so far away as had been thought, but the Russians refused to increase the number of detection stations the U.S. had first proposed. Since then, U.S. efforts have been directed at discovering means to improve the sensitivity of detection with the stations proposed. Last week, as negotiators prepared to resume the suspended talks at Geneva, word leaked of a report submitted to President Eisenhower which concludes that U.S. seismologists have achieved considerable success. Though the report itself is still secret, one major improvement has been sacrificed by its inventors--Paul W. Pomeroy and George H. Sutton of Columbia University's Lamont Geological Observatory.

Storm Trouble. The most sensitive way to detect distant earthquakes--or underground atomic explosions--is by measuring the long waves that travel along the earth's surface instead of striking deep into its interior. Drawback to this method is that even such minor disturbances as a storm at sea set up shorter surface waves (microseisms) that obscure or blot out the record. The Lamont improvement is an ingenious filtering device that separates earthquake waves from local confusion.

The new system is based on a type of seismograph in which a heavy weight is suspended so that it holds still while the earth waves move past it. The slight motion between the weight and electrical elements close to it creates a fluctuating electrical current. Before the current reaches the recording apparatus Pomeroy and Sutton pass it through a special galvanometer--a coil that makes a small weight move against the resistance of a delicate spring. The waves in which they are interested are long and of low frequency (40 to 50 sec.). They found that by choosing a galvanometer with the proper relationship between coil and spring, they could mechanically "tune" their system to register only long earthquake waves and filter out shorter microseisms.

Jumbles Made Sharp. The result was magical. Seismograph records that were hardly more than meaningless jumbles turned into clear, sharp records of distant earthquakes. When Dr. Sutton showed these records to a recent Washington meeting of seismologists, the contrast was so striking that the sophisticated audience burst into applause.

Pomeroy and Sutton are guarded about the effect their filters will have on international networks for detecting underground nuclear tests. They calculate that six stations equipped with the new instruments could detect most underground disturbances anywhere on earth that have the energy of a "nominal" (20-kiloton) nuclear bomb. Between 20 and 50 stations (v. the presently postulated 180) would be required not only to detect but also locate such disturbances. They are not prepared to estimate just how many more would be required to detect explosions of bombs as small as 5 kilotons or how accurately they could distinguish man-made nuclear earthquakes from natural ones.

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