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MILWAUKEE | Federal geologists confirmed Thursday that a minor earthquake occurred this week near the eastern Wisconsin city where researchers have been investigating a series of unexplained booming sounds.

The U.S. Geological Survey said the 1.5-magnitude earthquake struck Tuesday just after midnight in Clintonville, a town of about 4,600 people about 40 miles west of Green Bay.

Geophysicist Paul Caruso said that loud booming noises have been known to accompany earthquakes. He said the mysterious sounds that town officials have been investigating could be linked to the quake.

“To be honest, I’m skeptical that there’d be a sound report associated with such a small earthquake, but it’s possible,” Mr. Caruso said.

Earthquakes can generate seismic energy that moves underground at thousands of miles per hour, producing a sonic boom when the waves come to the Earth’s surface, Mr. Caruso said.

The U.S. Geological Survey says earthquakes with magnitudes of 2.0 or less aren’t commonly felt by people and are generally recorded only on local seismographs. Mr. Caruso said the Tuesday earthquake was discovered after people reported feeling something, and geologists pored through their data to determine that an earthquake did indeed strike.

Local residents have reported late-night disturbances since Sunday, including a shaking ground and loud booms that sound like thunder or fireworks.

City officials investigated and ruled out a number of human-related explanations, such as construction, traffic, military exercises and underground work.

COLORADO

4 students suspended in pepper-spray prank

NIWOT | Four students at Niwot High School in Colorado have been suspended after pepper spray forced a school evacuation.

Four adults and 45 students were treated by paramedics for respiratory problems and skin irritation after the pepper spray got into a ventilation system.

According to KMGH-TV, the suspended students could be charged with criminal use of a noxious substance if they fail to complete a justice program.

Mountain View firefighters decontaminated the building before students returned inside.

Niwot is between Boulder and Longmont.

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