(Reuters) - Geologists said small earthquakes may explain the mysterious booms, bangs and rumblings rattling residents of Clintonville, Wisconsin, who have flooded local police with hundreds of calls since early Monday.
The loud bangs, shaking or rumbling noises touched off a broad investigation by the town 40 miles West of Green Bay into possible causes such as someone setting off explosives, issues with the sewers, or explosions at a local landfill, city officials said.
Then the U.S. Geological Survey offered a possible explanation: a small earthquake registering magnitude 1.5 on the Richter scale was recorded at about 12:15 a.m. local time Tuesday morning.
"The quake we reported is very small," said Paul Caruso, a geologist at the U.S. Geological Survey in Golden, Colorado. "There may have been additional earthquakes that could be associated with the booms people are hearing."
Geologists said earthquakes create seismological waves underground that can cause noises when reaching the surface.
Some people might have felt the quake but the Geological Survey does not have much in the way of detection equipment in Wisconsin, so the small temblor was difficult to find.
"It was buried in the noise," Caruso said.
Clintonville City Administrator Lisa Kuss said on Friday she was satisfied.
"I don't think the work ends. I think the looking for reasons ends," she said in a telephone interview.
The city's investigation included checking water and sewer systems, a closed landfill, explosives permits for possible authorized blasting in addition to checking on possible geological causes.
Kuss said she had heard a bang and felt a jolt underfoot this week, while others said the sounds were more like booms accompanied by a rumble.
Clintonville police received 150 calls Monday night, 100 the second night, 40 the third and from eight to 10 calls each of the past two nights, she said.
"It is definitely dissipating," Kuss said of the reports.
The city has encouraged residents to call with any reports to track the sounds. Only one damage report of a cracked foundation has been received, but it was not clear what caused it, Kuss said.
(Reporting by David Bailey and Andrew Stern)