Clintonville, Wisconsin is an inland community, adjacent to Lake Pigeon.
USA Today reported on March 21, 2012 that a series of mysterious booms have been fraying residents’ nerves.
City administrator Lisa Kuss said the booms have roused people from their beds and into the streets — some in pajamas.
“It startled everyone. They thought something had hit their house or a tree fell on their roof,” Kuss said Wednesday. A police dispatcher took more than 30 calls from concerned residents between 5 a.m. and 7:30 a.m.
Possible explanations for the ruckus have been nearly exhausted, she said.
Residents have said they believe the booms come from underground. City officials have checked and rechecked methane levels at the local landfill, monitored water, sewer and gas lines, contacted the military about any exercises in the area, reviewed mining explosive permits and inspected the Pigeon River dam next to city hall.
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CNN reported on March 23, 2012 that the booms were due to a “swarm” of minor earthquakes amplified by the unique bedrock beneath the state of Wisconsin.
Speaking to Clintonville residents Thursday night, Lisa Kuss said the U.S. Geological Survey has determined that “our community did in fact experience an earthquake that registered 1.5 on the earthquake magnitude scale.” That minor quake was measured on Tuesday night by several mobile earthquake monitoring stations that were dispatched to the region, she said.
USGS geophysicist Paul Caruso said that Tuesday’s 1.5 tremor is only the second recorded earthquake in Wisconsin since 1947.
Caruso explained that the rock underneath Wisconsin and in much of the country east of the Rocky Mountains is “very consolidated” and without fault lines. And that means small quakes are actually felt by residents, unlike in California where the energy is absorbed.
Caruso said all seismic shifts generate noise but these sounds cannot be heard during major quakes.
“When seismic waves travel through the ground, they’re moving … faster than the speed of sound and when they hit the surface,” Caruso explained.
“(It) rattles the ground like a speaker … so it’s common for people to hear what they describe as sonic boom sounds accompanying earthquakes. But usually when there’s a big earthquake, people either don’t hear the sounds because the frequency is lower than the threshold of what humans can hear. Or other sounds going on (like) things falling down.”
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Steve Dutch, a geologist at the University of Wisconsin-Green Bay, said a 1.5 magnitude earthquake produces the energy equivalent of 100 pounds of explosives and could produce loud sounds.
But he was reluctant to describe Tuesday’s event as an earthquake, saying the term is generally used to refer to widespread stress in the earth’s crust. What happened in Wisconsin could be near the surface, perhaps caused by groundwater movement or thermal expansion of underground pipes, he said.
Still, Dutch said it was possible that the event could produce a series of sounds over time.
“If you’ve got something causing a little bit of shifting underground, it may take a while for whatever is causing it to play itself out,” he said.
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Clifford Thurber, a seismologist at the University of Wisconsin-Madison who served as a consultant for the city, is still on the fence.
“I won’t be amazed if it turns out to be earthquakes, but it could also be a near surface event, such as rocks fracturing beneath the surface due to erosion from flowing water.”
So far, the booms have only been heard within in a small, cigar-shaped area that encompasses most of Clintonville, Thurber says, suggesting an origin that is close to the surface, a possibility that falls within the uncertainty of the USGS seismic data.
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David Hill is an emeritus scientist with the U.S. Geological Survey in Menlo Park, California. Hill, who has written about such phenomena, said they have been around for a long time and have been reported all over the world.
“Back before the Industrial Revolution, Indians and early explorers talked about booming sounds in the northeast,” he said.
Powerful booms periodically rattle windows on the North Carolina coast. In upstate New York, residents near Seneca Lake call the phenomena the “Seneca Guns.” In Coastal Belgium, the sounds are called “mistpouffers,” or fog belches, Mr. Hill found. In the Ganges Delta and the Bay of Bengal, they are called “Bansal Guns.” People in the Italian Apennines call them “brontidi” or thunder-like, and residents of Shikoku, Japan, have dubbed them “yan.”
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Update: March 28, 2012
The booming and shaking continues in Clintonville.
Clintonville police say they received about 65 calls Tuesday night, from people reporting three or four loud booms. Officials say the calls came in from 10:35 until 11:40 p.m.
Authorities say the reports came from the same part of the city that has been experiencing the booms for more than a week. Several callers told police that these booms were stronger than those from last week, but no damage has been reported.
Geophysicist John Bellini says he looked at the nearby seismometers and was unable to detect anything Tuesday night.
Vibrationdata 