Back in the '80s, when he was a seismologist doing research at MIT, John Bullitt tinkered in his spare time with recordings of the earth's internal vibrations, trying to write computer programs that would speed up the data and turn it into sound.

He never quite got what he was looking for out of his recordings (or his other scientific research, for that matter), and soon left the professional science world to study Buddhism.

Two years ago, shortly before he was to turn 50, Bullitt began to feel like he and the earth had some unfinished business. He rented a studio space in Somerville, purchased some high-end sound equipment, and returned to his scientific work.

After several months of tedious labor, working to synchronize the vibrations recorded by a global network of digital seismographs and then shift their frequencies up a number of octaves and speed them up several hundred times to make them audible to the human ear, Bullitt was finally able to put on his headphones and listen to the internal orchestra of the earth in a way no one else had done before.

"I immediately burst into tears," Bullitt recalled. "It was just too beautiful. It made me feel wonderfully connected with the planet in an entirely new way."

He used his seismologic recordings as the basis for two projects which premiered last year - "Earth Dome," an immersive sound installation at his space in the Joy Street Artist Studios, which allows visitors to feel what it would sound like to sit inside of the earth; and the "Earth Sound," a CD which features a haunting track of the sounds generated by the huge 2004 earthquake that triggered the deadly Indian Ocean tsunami.

When it's not in a period of great upheaval, Bullitt's sped-up earth sounds have an underwater quality to them, punctuated occasionally by the billiard-ball clack of a minor earthquake. Some find the recordings very soothing, he said, especially children. Others find them haunting. Either way, he hopes that by making manifest what is normally beyond the reach of our senses, he can inspire appreciation for all that is happening beneath our feet.

"The surface of our planet moves up and down a foot twice a day," he said as he looked out the window of studio. "Yet we can't see it. Surf is crashing into the coast about 10 miles from here, vibrating the ground, but we can't feel it. Somewhere, an earthquake is happening, sending waves straight through the center of the earth, and yet we don't hear them.

"Sometimes my head spins when I think of all this stuff."

David Moulton, a sound researcher who has designed speakers for Bang & Olufsen, said that first listening to Bullitt's audio rendering of the earthquake was one of the most chilling moments in his musical experience.

"There's an authenticity to his work. It's real," said Moulton, who helped Bullitt tweak the finished product. "He's taking things that are outside our perspective and using sound as a lever to get them into our consciousness. There's a learning that happens as a result of that. I really think John is onto something powerful."

With a large project on the internal sounds of the human body already underway, and maybe another on the sounds of the underwater world to come, Bullitt sees his work as a bridge between science and art.

"I think good art and good science are two sides of the same coin," he said. "They just use different tools to peel back the layers and look for an underlying truth."

Though he says he'll never get back that first feeling of listening to the secret song of the earth, Bullitt will occasionally go into the black-curtained room that houses the sound installation and catch a glimpse of that moment.

"There's a connection to Buddhism there - slowing down, thinking about what's going on here, the deeper truths," Bullitt said as the crackle from a recorded earthquake rippled through the speakers.

"The planet has many stories to tell us. And the more we stop and listen, the better the choices we'll make in the long term."

FACT SHEET

Hometown: Lives in Cambridge, where he was born and raised. Family: Jane Yudelman, his partner of 15 years, is an international development consultant in developing countries; his daughter, Emily, 22, is studying library science at Emerson College. Education: He earned a bachelor's degree in physics from Grinnell College in 1980, and a master's in geophysics from the University of California-Berkeley in 1982. Hobbies: While he used to be a competitive swimmer, Bullitt says his life's work is his hobby. "Drawing, tinkering, listening, collecting sounds. It's all play."