SHARON, Pa. - Some residents of Mercer County, near the Ohio border, heard a bang or felt the Earth shake a bit Tuesday night. The noise and accompanying vibration were reported from Hubbard to South Pymatuning Twp.

"It was like something hit the house," people reported over and over again.

While he can't say with scientific certainty, geologist Lindell Bridges said he believes the sound came from a phenomenon known as a cryoseism - more commonly known as a frost quake.

"I think it's a very good possibility," Mr. Bridges said of the clamor and vibrations. "I think that's exactly what you heard."

The president of Pure Earth Resources LLC in Sharpsville is called upon for his services in the oil, gas and mining industries. And while he never has experienced a frost quake firsthand, he believes there's a strong case to be made that such an event occurred in the area.

"It's pretty uncommon for it to happen - but that doesn't mean it didn't happen," he said.

During the past few weeks, frost quakes have been reported in Canada, Wisconsin, Vermont, Cincinnati and elsewhere.

Two primary elements are needed to trigger frost quakes - water-saturated ground and a sharp drop in temperature. Both conditions were present; heavy rain last week soaked the ground, and in recent days temperatures rapidly dropped more than 40 degrees.

Frost quakes occur mainly at night when temperatures bottom out. As the water in the ground freezes, it expands and cracks the soil, bedrock or stones around it to create room. "It's something like an earthquake," Mr. Bridges said. "The reason you get an earthquake is stress builds up in the ground and it breaks and releases stored-up energy."

Besides the sound and vibration, people have reported seeing distant flashing lights before or during frost quakes. Those likely are caused by electrical changes when rocks are compressed.