UNR Seismo Lab spied meteorites

By Mike Wolterbeek
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RENO, Nev. – When the Sutter Mill’s meteorite streaked across the Nevada sky in April, it made a loud boom and shook homes throughout the region. Ken Smith, associate director for the Nevada Seismological Laboratory at the University of Nevada, Reno, heard it and felt it that Sunday morning. His scientific curiosity drew him right to the lab’s earthquake monitoring network to see what registered on the more than 150 reporting stations. He found an astonishing series of registrations.

“I knew it wasn’t an earthquake, it sounded and felt like an explosion,” he said this week, reflecting on his participation as co-author in an article just published in the prestigious journal Science. “All along the western part of the state, the network had lit up. Recording stations in Mammoth Lakes, Calif., and Pyramid Lake and Walker Lake here in Nevada, picked it up, but I used our recording stations around the Tahoe Basin, Sierra Valley and some other California recording stations to track its trajectory.

“The seismic network is like a big antenna; usually we look down, into the ground with the antenna, so basically I turned the antennas upside down and analyzed the data from the huge shockwave from the meteor as it made a wake like you’d see in the front of a boat through the atmosphere.”

The low angle and relatively slow speed of the pieces of the 100,000-year-old, 40-ton asteroid as it broke up 30 miles above the ground made it easy for the network to record its path from about 60 miles east of Reno to its impact in El Dorado County, Calif., about 85 miles to the southwest of Reno. It took the sonic waves from the meteorite about four minutes to reach the ground traveling at about 10 feet per second. A seismic wave from an earthquake travels about four miles per second.

The article in Science is very technical and is mostly about mineralogy and petrology, the origin or rocks, but Smith’s contribution, which ended up at about one paragraph, is that he helped the other scientists locate the impact area quickly, which enables quick recovery of the fragments, before they are weathered and altered by Earth’s atmosphere.

“They mostly used radar in California to confirm the estimates of elevation for the fragments; we had the best estimates of the altitude of the explosion, which was the greatest altitude of a meteorite explosion ever recorded,” Smith said. “The energy of the fireball was about 4 kilotons of TNT as the piece of asteroid blew from about 2 to 4 meters in size to small fragments. Most of it vaporized.”

The primary author of the article in Science magazine is Peter Jenniskens of the SETI Institute, which seeks out intelligent life in the universe. The article has about 50 co-authors in many scientific disciplines from around the world.

The Nevada Seismological Laboratory is a research and public service division within the University of Nevada, Reno’s College of Science.

Mike Wolterbeek

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EldoradoJanuary 16, 2013 - 3:48 pm
None of the figures calculate.. Sonic waves in air travel faster than 10 feet per second and it if was 30 miles up, at that speed it would take a lot longer than 4 minutes. Also, I thought they said it was over 4 billion years old, not 100,000. If it was 30 miles up and 60 miles from Reno when it exploded, it would travel much further that 25 more miles to Lotus... NASA has photos of it far west of Reno and still in one piece, even though the scientists originally said it exploded over Reno.
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