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Russian Seismic Event Evokes Questions about Nuclear Tests

By R. Jeffrey Smith
The Washington Post

For the second time in the past two years, the Clinton administration has asked the Russian government to explain suspicious seismic signals emanating from its former Arctic nuclear test site and to allay concerns that the signals might have come from a prohibited underground nuclear test.

The questions arose after seismic sensors maintained in the region by Russia, the United States, Norway and Finland picked up an unusually powerful signal originating near the island of Novaya Zemlya on Aug. 16. Some features of the signal appeared to be characteristic of a man-made explosion instead of an earthquake, U.S. officials said.

White House and Defense Department spokesmen said Thursday the administration has reached no conclusion on the signal's cause and that it is discussing the matter with the Russian government. Officials in Moscow expressed surprise at the U.S. statement and strongly denied any nuclear test had been conducted.

Russia promised in 1992 that it would not conduct further nuclear explosions and last year signed the Comprehensive Test Ban treaty barring such blasts. The treaty has not yet gone into effect, but the more than 146 nations that signed it are legally bound by its provisions under a common reading of international law.

The signal was generated by an event with a magnitude of 3.8 on the Richter scale, making it comparable to the detonation of up to 100 tons of TNT. "This one certainly had characteristics that at least would lead some to believe that there had been an explosion," said Pentagon spokesman Michael Doubleday.

Other officials explained that the signal was marked by sudden compression of the earth rather than the shearing and fracturing motion more common in quakes. But a key question is the "epicenter" of the signal, a matter still being studied. The latest U.S. analysis indicates it was most likely offshore near the site of a 1986 earthquake, according to three knowledgeable sources, but some possibility still exists that it occurred on the island.

The issue is complicated by U.S. intelligence satellite data indicating that Russian scientists have been unusually active at the test site in the past few months. Technicians there have been flying in helicopters, lowering equipment, plugging test holes and stringing cables for diagnostic equipment, according to many sources. Viktor Mikhailov, Russia's minister of atomic energy, visited the site several weeks ago.

Russian officials have explained that they are conducting or preparing to conduct so-called "sub-critical" nuclear tests, in which chemical explosions are used to blow apart fissile material but no nuclear chain reaction occurs. The Energy Department conducted sub-critical tests earlier this summer, sparking protests from peace groups alleging they violated the spirit of the comprehensive test ban treaty.