Credit: AFP
In the mid-1990s, Terry Wallace, now at America's Los Alamos National Laboratory, was part of a team studying earth movements in the Andes Mountains along the border between Bolivia and Chile. Occasionally, one of the seismometers would record strange micro-earthquakes, less than 1.0 on the Richter scale. Small temblors are common, but these occurred only late at night in a remote plain, 4,000 metres above sea level.
Most people associate seismology with earthquakes, but Wallace knew that seismometers aren't picky about the source of vibrations. Given the remote location, he wondered, could he be detecting trucks, carrying contraband though the desert?
Poring over the seismograph traces, he came to believe he could even determine in which direction the smugglers were going, based on the fact that from one side, they would be approaching across flat land, whereas from the other, they would be going uphill. On the upgrade, the trucks would have to gear down, producing different vibrations.
So, one night, he hid and watched as trucks, running without lights, rolled across the plain. Staking out South American smugglers in a remote desert wasn't, he would later admit, the smartest thing he'd ever done. "But it was fun," he said. More significantly, it was an early exercise in what has come to be known as 'forensic seismology.'
Forensic seismology originated during the Cold War as a means of monitoring the enemy's underground nuclear tests. But it is a field whose uses are as broad as the imagination.
In 2000, Emile Okal of Northwestern University in Ohio used it to track a gigantic iceberg as it floated away from Antarctica, scraping across the sea bottom as it went. Vera Schulte-Pelkum, from the University of Colorado, in Boulder, has used it to monitor storm waves crashing into Canada's Labrador coast so hard that they show up on seismometers in California.
But the most interesting investigations involve airline crashes, mine disasters, and explosions.
The key to such studies lies in the fact that seismometers are common. By one estimate, a few years ago there were 16,000 of them permanently installed around the globe, many continuously uploading to the Internet.
Once a seismometer is installed, it's always tuned in. "You may be trying to listen to one thing, but the 'noise' may tell you something unexpected," Wallace has said. "We're just beginning to eke out every wiggle on the seismogram and what it's telling us."
Canadian seismologist David McCormack set the groundwork for this type of analysis in the investigation of Pan Am Flight 103, brought down in 1988 over Lockerbie, Scotland, by a terrorist's bomb.
