Scientists exploded a powerful nuclear weapon Friday deep beneath the Nevada Test Site in the third announced nuclear test of the year.
The blast, which had been delayed twice previously, had a yield of up to 150 kilotons, the largest allowed under existing treaties with the Soviet Union.
The explosion registered 5.0 on the Richter scale at the National Earthquake Information Center in Golden, Colo.
"It was pretty good sized, but some register as much as 6.0," said Bill Schmieder, a geophysicist at the center. "I would say it was in the medium range."
The Energy Department said the test appeared to go smoothly, with no apparent release of radiation.
Seven Soviet scientists, who are staying at the site while preparing for joint verification experiments sometime this summer, were kept at the small settlement of Mercury, about 40 miles from Ground Zero. They were not allowed to monitor the blast, according to a spokeswoman for the Department of Energy.