This much is certain: Nancy Fitzhugh's home shakes.

But no one can figure out why.

Fitzhugh, who has lived on Stoneway Drive in Chester near Lewis Road for 17 years, says her house has been gently but consistently trembling for the past three years.

Lack of sleep and minor household repairs she says are related to the issue are stacking up, she said.

"I don't want to mortgage my house, but something has to give. I've got earthquake insurance, but I don't think I'm having an earthquake here by myself," said Fitzhugh. "There's no living in peace anymore."

Fitzhugh speculated that blasting and mining activity at Vulcan Materials Co.'s Dale Quarry about a mile and a half from her home had something to do with it. But investigations find otherwise.

Seismic monitoring at the home in 2007 and 2008 by a consultant commissioned by the quarry found that while low-level, high frequency vibrations were indeed occurring regularly, they were not related to the operation's activities.

Two separate investigations by the state's Department of Mines, Minerals and Energy reaffirmed that, concluding that the reported vibrations were inconsistent with the times and dates of the operation's blasting and mining activities. The department also says the vibrations detected were not strong enough to have caused damage to the home, nor would an average person feel them.

"We don't know what to tell her quite frankly," said Michael D. Abbott, a spokesman for the state mines and energy department, noting that the department would be looking into the complaint for a third time. "We've not been able to a put a finger on what it is that she's experiencing. This is an unusual situation."

The findings from Sauls Seismic Inc. found 653 vibrations inside and outside the home at various times, day and night, including weekends from Dec. 3, 2007, to Jan. 18, 2008.

Chesterfield County hasn't been able to solve the mystery either.

"I spent a tremendous amount of time trying to determine what's going on," said Roger Robertson, chief of inspections for the county. "I'm not doubting that that she's experiencing something -- it's just that we can't determine what it is. She might be tuned into some frequency that most of us don't pick up on."

Shelby Kondas, a friend of Fitzhugh's from Northern Virginia who stayed with her last week, said she'd felt the trembling firsthand on several occasions.

"It was like somebody was underneath the love seat shaking it," she said. "It was kind of nerve-wracking."

Most surrounding residents said they did not experience the shaking.

Retired Chesterfield Fire chief and fellow Chester resident Robert Eanes has a theory: ordnance fire from Fort Pickett, 30 miles away.

"I live less than 1 mile as the crow flies from this lady. It's been a phenomena for the 21 years I've lived here that when they shoot ordnance in Blackstone, my windows and doors at times rattle," he said, offering that an underground rock formation carries it the distance. "To me, it's not even an irritant, it's the sound of freedom."

Lt. Col. David Weisnicht at Fort Pickett said there is a granite shelf that runs to Chesterfield, but a different part, and said feeling the effects of artillery fire at that distance was unlikely.

"I would be most doubtful that that was occurring, but I would be amenable when we're firing to go up and stand at her house," he said.