BAYOU CORNE —As the driver revved up his vibroseis seismic exploration truck’s engine, the Sportsman’s Landing parking lot hummed and the gravel actually vibrated.

About 40 people attending the Saturday morning demonstration felt the vibrations from the oil patch “thumper truck” start in the soles of their feet and shimmer up their bodies.

“That was a little weird, I didn’t know it would feel like that,” said Marilyn Pritchard. She and her husband have been displaced from her Bayou Corne home ever since the now-8.6-acre sinkhole appeared in a swamp near their neighborhood on Aug. 3.

The “mast” of the Boone Exploration Inc. truck, a large, thick pad connected to the truck’s frame, was pressed firmly to the ground by giant hydraulic cylinders, then turned on, or “shot,” to vibrate for 10 seconds.

A few yards away from the crowd, a round, white plastic pad, which looked like it came off a commercial floor buffer, housed a geophone that picked up the vibrations and sent electronic signals via thick cables to a nearby recording box that radioed the signals to recording trucks. Hundreds of “shots” will be taken around the area to create a three-dimensional map so scientists can determine what is going on underground in the vicinity of the sinkhole and Bayou Corne.

When the plan to use the truck on area roads near homes was announced at a recent community meeting, some residents, including the Pritchards, expressed fears the vibrations might stir up termites or even crack walls and windows.

“We had our termite man out this week, that’s why we came back (from Baton Rouge),” Pritchard said.

“I thought it was great. Now I know what to expect,” Pritchard said of Saturday’s demonstration. “They said it would feel like a garbage truck, but our garbage truck doesn’t feel anything like that.”

Sonny Cranch, spokesman for Texas Brine Company LLC, said the demonstration was put on Saturday specifically to “allay fears” that residents might have of the truck’s seismic effects.

“There were some folks who were concerned it was going to shake their houses off their foundations and we just wanted to show them how benign it is,” Cranch said. “And show them how the geophones (recording boxes) will be set up in their yards and to be as noninvasive as possible.”

Although the vibroseis seismic exploration trucks are commonly called “thumper trucks,” Cranch said that is a misnomer. “At one time they may have thumped,” he said, but now modern trucks send a range of low- to high-frequency vibrations as deep as 7,000 feet underground.

Bob Payne, who lives in Thibodaux but owns property in the nearby swamp, said he attended the demonstration to find out more about the upcoming seismic imaging project.

“I think these people know what they are doing,” Payne said. “I’ve got a wait-and-see attitude how it’s all going to fare out. I believe there are some conflicts of interest between the companies that are involved and the people and the government, but at the same time the scientists will eventually figure out what’s going on and the truth will be told.”

Teleca Donachricha, who lives nearby but has not been displaced from her home, was video-recording the demonstration to post on YouTube and Facebook for residents who could not attend.

“I’m OK (with the truck) and I’m OK with them doing whatever they need to do to get the situation fixed,” Donachricha said.

The situation, as she called it, has been going on so long it’s dividing the community.

“People are tired of this,” she said. “People are irritable and saying things to each other they regret. There are some people that want a buyout, and because they want that buyout, they’re not willing to do anything to help the situation and to improve it.

“Then, there’s people that don’t want a buyout that are saying ‘Do whatever you gotta do if that’s what its going to take to get it fixed,’ ” Donachricha said.

Texas Brine spokesman Cranch said the seismic tests are just getting under way more than six months after the sinkhole appeared because the company only recently received permission from all the affected landowners.

Scientists believe the failure of a Texas Brine Co. LLC salt cavern deep underground in the Napoleonville Dome, located in the swamp between the communities of Bayou Corne and Grand Bayou, caused the sinkhole that has grown to 8.6 acres.

Crude oil, natural gas and methane trapped in natural formations along the dome’s salt face were released, causing the evacuation of about 150 nearby residences.

Salt domes in the Gulf Coast result from the geologic uplift of massive fingers of salt from a deep subterranean layer known as the Louann salt.

About 150 million years ago in the Jurassic period, this so-called “mother salt” began to be laid down by the evaporation of an ancient, shallow sea not fully connected to the open ocean.

In modern times, the Napoleonville Dome has been the focus of oil and gas exploration, brine mining, as Texas Brine does, and hydrocarbon storage in the cavities left by brine mining.

David Mitchell contributed to this report.