U.S. intelligence agencies say, based on preliminary indications, that North Korea did not produce its first nuclear blast yesterday. U.S. officials, speaking on the condition of anonymity, said that seismic readings show that the conventional high explosives used to create a chain reaction in a plutonium-based device went off, but that the blast's readings were shy of a typical nuclear detonation. "We're still evaluating the data, and as more data comes in, we hope to develop a clearer picture," said one official familiar with intelligence reports. "There was a seismic event that registered about 4 on the Richter scale, but it still isn't clear if it was a nuclear test. You can get that kind of seismic reading from high explosives."
The underground explosion, which Pyongyang dubbed a historic nuclear test, is thought to have been the equivalent of several hundred tons of TNT, far short of the several thousand tons of TNT, or kilotons, that are signs of a nuclear blast, the official said. The official said that so far, "it appears there was more fizz than pop."
White House spokesman Tony Snow said assessing the validity of North Korea's claim of a successful nuclear test could take several days. "We need to find out precisely what it is that took place yesterday, and that is something that's going to take awhile for the scientists and others to work through," Mr. Snow said. "Nobody could give me with any precision how long it will take until they can say with certainty what happened."