Seismographs show explosion timeline

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The explosion on the south side Saturday was so powerful it showed up on earthquake monitors. That information could be critical to investigators.

"The house shook a little. I'm ten minutes away. I seriously thought something hit our house," said Marjorie Basey.

It also rocked the night.

"It definitely felt like something was hitting. The whole house shook," said Nick LaVell.

Dr. Michael Hamburger, a geologist at Indiana University, says "there was a lot of energy that went into the atmosphere, which all the neighbors and residents know."

That energy was picked up on earthquake-measuring devices at Franklin Central High School, seven miles from ground zero.

"It turns out the atmospheric wave, like a sonic boom, translates into vibrations. Our instruments in the ground picked it up," Hamburger said.

The earth shook, but it was the sound wave that really rocked the seismometer.

Hamburger showed us a graph with a small flutter of activity from the seismic pen.

"This first vibration," he said, "is actually the ground vibration. It arrives just a few seconds after 11:08 in the evening."

That time is significant. For the first time, we have a time stamp for the event measured by sensitive scientific equipment. Something that could be critical, especially if this becomes a criminal case.

"It looks to me that it must have been a pretty instantaneous thing," Dr. Hamburger said. "Just a fraction of a second."