FORENSIC SEISMOLOGY

Seismic networks increasingly are being used to provide insight into the timing and nature of chemical explosions associated with accidents, crimes, and acts of terrorism. Examples of such use of seismographic data, known as forensic seismology, include analyses of the April 19, 1995, Oklahoma City terrorist bombing; the August 10, 2000, explosion that sunk the Russian submarine Kursk; the August 19, 2000, New Mexico gas pipeline explosion; the September 11, 2001, plane crashes into the World Trade Center and Pentagon; and the February 1, 2003, Space Shuttle Columbia accident. Following the bombing of the Alfred J. Murrah Federal Building in Oklahoma City, seismic recordings were used to confirm that only a single bomb had been detonated and also to estimate the size of the bomb. Conspiracy advocates had proposed that the two accused bombers, who were ultimately convicted, had been set up. It was speculated that their bomb was used as cover for a larger and more damaging bomb, detonated by the U.S. government. The seismic recordings clarified the bombing scenario and publication of the results discouraged a conspiracy defense by the accused bombers. Seismic recordings of explosions that doomed the Russian submarine Kursk revealed details that otherwise might have remained Russian state secrets and helped rebut the Russian contention that a foreign vessel had collided with the submarine. The recordings indicated that a small 50 to 100 kg (equivalent TNT) explosion preceded the main 3- to 7-ton explosion by about 2 minutes, suggesting that a torpedo may have detonated and set off the sequence of events that sank the submarine. Analysis of the seismic signal of the main explosion also indicated that the resulting gas bubble was generated at near-bottom water pressures. Seismic recordings of the New Mexico gas pipeline explosion indicated multiple ignitions. The time between ignitions, recorded at nearby seismometers, helped determine the degree of pain and suffering (and cost to the pipeline company) of the 11 victims of the explosions in a lawsuit brought by relatives. Distant seismic recordings of the September 11, 2001, collapses of the two towers of the World Trade Center were used to constrain and show that ground shaking generated by the collapses was not a major contributor to damage or collapse of surrounding buildings.