Word: seismicity
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...Geneva last summer concluded that a worldwide system of 180 inspection stations could detect nearly all underground nuclear tests. Any explosion of even the modest energy of 5 kilotons, they figured, could be distinguished from the noise made by small earthquakes and other natural causes. Only about 100 seismic "events" a year would be borderline cases. These could be followed up and checked by other means...
...weeks ago the U.S. Government announced that new information has cast doubt on the effectiveness of the 180-station system. Last week the U.S. Department of Defense released the data that led to this conclusion. To measure the seismic effects of underground tests, 16 special seismographs were set up in a line extending from the Nevada atomic proving ground to Maine, 2.500 miles away...
...right, but not quite as strongly as had been anticipated. At distances above 700 miles, only explosions of more than 20 kilotons could be identified clearly as manmade. To sum up, said the panel, the 180-station detection system might be confronted by 1,500, not 100, natural seismic shocks a year that could not be distinguished from an underground test explosion. This number would presumably overburden the checking system as presently outlined...
...strength of results of a single 1957 test, President Eisenhower's Science Advisory Committee estimated that underground atomic blasts down to five kilotons could be fully detected by seismic inspection stations. On the basis of the five-kiloton report, the U.S. settled down with the Russians at Geneva to try to negotiate a stop-tests agreement with an inspection and detection system-but fully aware that the chances of detection were slim below the five-kiloton underground threshold...
Each of these methods, the East-West experts pointed out, has its faults. Acoustic waves from a volcanic eruption, for instance, can be mistaken for waves from a nuclear test. Seismic waves from earthquakes can be misinterpreted, too. Nuclear tests deep under the earth or ocean yield no radioactive fallout, send out no air waves or radio waves. But they do send waves through the ocean, the earth, or both. Each type of test is detectable by one or more methods...