That mysterious “boom” some heard early Friday in Niagara County was a small earthquake.

The U.S. Geological Survey reported a tremor with a magnitude of 2.5, at a depth of approximately three miles, was recorded shortly after midnight almost four miles east northeast of Olcott.

Police agencies in Niagara County said they received numerous calls at about 12:45 a.m. Friday from residents of rural Niagara County and even Canada. Residents reported a loud noise and shaking windows.

The tremor was recorded at Columbia University’s Lamont-Doherty Earth Observatory in Rockland County just a second before 12:35 a.m.

“It’s a shallow earthquake, relatively speaking, but it’s so minor,” said Michael C. Constantinou, director of the Structural Engineering and Earthquake Simulation Laboratory at the University at Buffalo. “It’s not in the lake [Ontario]; it’s on land.”

The earthquake occurred in an area with no recorded history of faults, according to Constantinou.

“The more it opens up, the larger the area, the stronger the earthquake is,” he said. By comparison, he said, a fault that opened in 1960 along coastal Chile – resulting in a magnitude 9.5 quake and tsunamis that reached the Philippines and Aleutian Islands – was the size of California. An earthquake measuring 2.5 would be felt by people in close proximity. However, “I live 10 miles away from there and I felt nothing,” Constantinou said.

Further, an earthquake of that magnitude is unlikely to cause damage, he said.

“There are thousands of these every year worldwide,” Constantinou said.

But an interesting point about Friday’s tremor was its proximity to the power plant in Somerset, approximately a mile and a half away. “Too close,” he said.

A spokesman for Upstate New York Power Producers, which bought the coal-fired plant earlier this year, couldn’t be reached to comment.

The last tremor felt in the Buffalo Niagara region was Aug. 23, 2011, when the ripple effects of a magnitude 5.8 quake centered near Richmond, Va., reached this area. Before that, a 5.0 quake that originated near Ottawa, Canada, was felt here on June 23, 2010.