A bit of "forensic seismology" has revealed details of the Kursk tragedy that otherwise would have remained state secrets. Seismologists last summer picked up not only the death throes of the Russian submarine but also a smaller precursor boom--suggesting that by the time of the big explosion, the sub's fate may have already been sealed.
On 12 August, the fatal day, an odd seismic signal was picked up at monitoring stations all around the southern Barents Sea, where the sub sank. Soon after seismologist Terry Wallace of the University of Arizona in Tucson heard of the accident, he and his colleagues decided to investigate. They used techniques for monitoring nuclear testing to determine that the signal had come from an explosion, not an earthquake. The hefty blast was equivalent to between 3 and 7 tons of TNT--two or three times the size of the Oklahoma City truck bombing. And it had happened at the very spot where the Kursk went down.
Wallace also noticed a much smaller explosion--at about 50 to 100 kilograms, about the size of the detonation of a torpedo--preceding the main event by 136 seconds. Apparently, it was this explosion that sank the sub. The sub was already near the bottom by the time the main explosion went off, he says, because analysis of the seismic signal from the resulting gas bubble indicates near-bottom pressures. Together, the two signals provide further evidence against the notion that the Kursk suffered an underwater collision. Speculation in the media has been that the Russians were experimenting with an exotic propellant for their high-speed torpedoes when disaster struck.
The seismologists continue to pick up noises from the vicinity--apparently from depth charges the Russian Navy has reportedly been dropping to discourage rubberneckers.
The Kursk analyses are "another example of the tremendous and continually improving capability to detect and identify small seismic events," says Gregory van der Vink of the Incorporated Research Institutions for Seismology (IRIS) in Washington, D.C. Such capability is vital for enforcement of the Comprehensive Test Ban Treaty. Would-be violators, he says, should note that the Kursk explosion was tiny compared to even small nuclear blasts.