The Kursk—one of the largest submarines ever built and the pride of the Russian Navy—sank to the bottom of the Barents Sea on Aug. 12, 2000, during the Northern Fleet’s largest exercise in more than a decade. The mystery only deepened as Russian officials put forth conflicting explanations for the tragedy, which claimed 118 sailors.
Now, scientists report that analysis of the shock waves recorded at seismic stations across northern Europe indicate that the Kursk sank after onboard explosions, possibly of missile warheads or fuel. The researchers from the University of Arizona in Tucson and Los Alamos (N.M.) National Laboratory present their findings in the Jan. 23 Eos, the weekly newspaper of the American Geophysical Union in Washington, D.C.
Patterns of ground movement generated by explosions differ from those caused by earthquakes, explains Terry C. Wallace, a University of Arizona seismologist and a coauthor of the Kursk analysis. Using the techniques of forensic seismology, he adds, researchers studying these vibrations can discriminate causes of explosions as diverse as underground nuclear testing, terrorist bombings, and detonations in fireworks factories.
Underwater explosions send out a distinctive pattern of pressure waves known as a bubble pulse, which stems from oscillations in the rising bubble of hot gases. Because water is a nearly incompressible fluid, the pressure pulses from even small underwater blasts can generate strong seismic signals when they strike the lake or ocean bottom.
“You could throw just a couple of sticks of dynamite into Lake Michigan, and seismometers all over Michigan would detect it,” says Wallace.
The seismic data captured by the European instruments include two bubble pulses. Only a few seismometers captured the first blast, which the scientists estimate released energy equivalent to 250 kilograms of TNT—about the energy of a modern torpedo, Wallace notes. The second explosion occurred more than 2 minutes later and was detected up to 3,100 miles away. That blast released 18 times as much energy as the first, about the same as that in the fuel and warheads of eight Russian ship-to-ship missiles.
Soon after the submarine sank, some Russian officials claimed that the Kursk colliding with another vessel caused the first set of seismic signals and the sub striking the ocean bottom produced the second set. The time that the second pressure pulse took to reflect from the ocean surface and return to the bottom, Wallace says, indicates that it was probably generated when the Kursk was on or near the ocean floor, about 100 meters below the surface. Also, he contends, simple collisions wouldn’t create a bubble pulse.
Wallace’s team used openly available data recorded at some of the more than 16,000 seismometers installed worldwide. Unfettered access to such data is vital both for the study of natural phenomena and for verifying the details about incidents such as the loss of the Kursk, says Frank L. Vernon, a seismologist at the Institute of Geophysics and Planetary Physics in La Jolla, Calif.