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Seismology in Action

As a seismologist, Associate Professor of Physics Maggie Benoit looks at squiggles.

“Whenever there is a big signal from anything, I usually go to the seismic data and look it up so I can see it,” she said.

A big signal came earlier this week from a gas explosion at a nearby townhouse community in Ewing on March 4 and Benoit and a colleague quickly got to work dissecting the data.

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The reading from a seismograph in Allentown, NJ after the Ewing explosion on March 4, 2014.

“Seismologists are able to tell, by looking at the waves, whether something was an explosion or an earthquake,” she said. “And so this figure is classic explosion. It’s a textbook seismogram of an explosion.”

After the explosion six miles away from the College, Benoit and a colleague were able to determine how far away the blast was heard and felt.

A scientific microphone called an infrasound sensor picked up the blast’s airwave in rural Allentown, NJ, about 20 miles southeast of TCNJ.

“The explosion set off a sound wave,” she explained. “We hear it as sound, but it’s really energy that’s moving and vibrating the air particles. It’s picked up by our ear drum as it vibrates back and forth, and the microphone also vibrates back and forth as that wave of sound moves past it.”

“If someone was sitting in their house and it was really quiet, they could’ve heard the blast at 50 kilometers [about 31 miles] away, based on the data we have,” Benoit said.

The explosion was felt as well as heard, but Benoit said it would have registered at less than a 1 on an earthquake magnitude scale. To put that into perspective, the Virginia earthquake in August 2011 that shook the ground in New Jersey registered at a 5.8 magnitude. The seismic wave that traveled through the Earth during the explosion measured at 30 micrometers per second, whereas the 2011 earthquake moved through at 2,000 micrometers per second.

“Anytime there is energy released anywhere in the earth you can pick up a seismic wave,” she said. Benoit’s colleagues at the University of Washington look for seismic signals whenever the Seattle Seahawks score a touchdown. “They can see the seismic signal of the fans jumping up and down in the stadium,” she said.

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