We know where you are and what you are doing...

Terry Wallace, LANL
 

A foot fall in the Sonoran desert, waves crashing on a beach 700 kilometers away, strong winds swaying clock towers and sky scrapers, trucks bouncing down a dirt road, an explosion 5000 kilometers away… What do these have in common? Each can be detected by measuring the energy they transfer as sound waves into the solid Earth. One can locate smugglers, predict weather, and deduce who is playing with bombs by using these sound or seismic waves. Sensitive instruments called seismometers can pick up these forms of Earth “noise”. Most seismologists, scientists who use the data from seismometers to understand the origin of these vibrations, focus on earthquakes. But, a growing number now focus on monitoring and documenting human behavior and human caused events, a field called forensic “seismology.”
 
Forensic seismology got its start in studying seismic signals for indications of nuclear testing by other nations. More recently, forensic seismology has been used to unravel the mysteries of plane crashes, pipeline bursts, and the Murrah Building bombing in Oklahoma City in 1995. The controlled demolition of a Seattle stadium was studied through its seismographic records. And the bombing and collapse of New York's World Trade Center in 2001 appeared on seismograms, too.
 
In this presentation, we will unravel two whodunit stories to show how sound waves and a bit of ground work can reveal the details of disasters with no survivors to tell the story.
 
On 12 August 2000, the Russian Oscar II class submarine Kursk sank in the Barents Sea, killing all 118 sailors and officers aboard. While the Russian authorities were denying the tragedy, vibrations from the event were picked up by seismometers. Seismic stations recorded two explosions that corresponded to the Kursk disaster in time and place. At one point, the Russians suggested that a spying American submarine may have been the cause of the explosions, setting off international worry about what these superpowers might do. Here’s what they discovered: The first explosion was 250 times smaller than the second one, and the second seismic signal came 135 seconds later. With these clues and a bit of detective work, it was possible for seismologists to construct a detailed scenario for what happened aboard the submarine, to provide families with a clearer picture of what happened to their loved ones, and to extinguish a potential international tiff.
 
On 19 August 2000, a natural gas pipeline exploded in southeastern New Mexico near the Pecos River. A hole over 20 meters deep and 80 meters long formed due to the explosion. Eleven people camping nearby died. The seismic data show three distinct events: the initial blowout and two subsequent ignitions. It also shows how long the campers had to react between the initial blowout and the primary ignition and how long the explosion lasted. What caused the explosion? Why were there two ignitions separated in time? Could this have been prevented?
 
We will explore these disasters and the power of forensic seismology in monitoring motion in far-away places in this interactive Café.
 

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