A spate of mysterious booms that has been shaking central Oklahoma returned for a second day Friday, again rattling houses and frightening livestock.
Oklahoma Geological Survey research seismologist Austin Holland said a series of booms, much like a sonic boom, rattled the Norman area starting at 11:19 a.m. Friday. Numerous others had been reported Thursday in the same area at about the same time.
Friday's booms weren't "quite as frequent" as Thursday's, Holland said. "It's quite interesting."
The windows of Anthony Young's home in the town that's the outskirts of Oklahoma City rattled. "We thought some nut was out here, you know, with explosives," Young told KOCO-TV. "It sounded like thunder, you could feel the ground shake, but it was nothing like an earthquake"
Both Holland and National Weather Service meteorologist Matthew Day didn't have an explanation for the booms.
No earthquakes have been recorded in the area, Holland said, noting that "we would have seen them on our seismic stations in the area." And it's unlikely that it's due to a drilling process known as fracking, he said, because the booms were heard and felt over a wide area including Norman, Edmond and Shawnee.
Holland's best guess: It must have been something just above the surface of the earth or in the atmosphere.
Day, who's based in Norman, said a phenomenon known as cryoseisms also isn't likely. Cryoseisms, or "frost quakes," occur when water quickly freezes in soil or rock, then expands and cracks.
"There are some stories going around that's what it was, but based on the research we've done here, it doesn't appear what people heard is related to the cryoseism phenomena," Day told The Norman Transcript. "There's not enough moisture, and the temperatures are not cold enough. That happens in areas where you have a lot of water flowing through a lot of rock," Day said.
"We don't know what it was, we just know what it is not," according to Day.
Holland said the booms occurred on generally regular interval, initially occurring 40 to 60 seconds apart, then about 20 seconds apart.
"It's a mystery to us as well," he said.
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