Irving, Texas (CNN) Jim and Gail Wells have lived in the upscale Las Colinas area of Irving, Texas, for 14 years.

Nestled between Dallas and Fort Worth, they love their quaint neighborhood for its custom homes amid rolling hills and large trees.

One of the neighborhood's newer features is a spate of seismic activity.

According to the U.S. Geological Survey, the Dallas area has suffered almost 40 small earthquakes (magnitude 2.0 or higher) since the beginning of this year, the latest a magnitude-2.7 quake near Farmers Branch on Saturday . Many of the epicenters were recorded in Farmers Branch and Irving, with a couple to the south in Venus.

"The quakes don't sound like much to somebody from California," Jim Wells told CNN. "But when you are sitting right on top of them, they are more than noticeable. They will shake the entire house, and you have no doubt about it when you have gone through it. We have in my home perhaps 100 or more wall hangings, pieces of art -- prints, etchings, oil originals -- and none of them are hanging straight."

On January 7 and 8, Irving experienced 11 earthquakes in about 24 hours. During one of those quakes -- a magnitude 3.6 -- Gail Wells says the rattling and shaking were so intense it knocked her off the sofa.

Susan Hough, a seismologist at the USGS and the California Institute of Technology, says the epicenter of these types of earthquakes would produce "average-to-high shaking intensities close in, but low intensities" about six miles out.

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The Wells' home sits less than a mile from the epicenter of some of the Irving quakes, and they say they've felt at least 15 of them this year. Though there hasn't been "serious" damage yet, Jim Wells is worried there will be if the quakes continue.

"I don't think that there is much doubt that there will eventually be damage to the pier and beam structures. There should be damage to the brick facades should it continue, and, of course, damage to the sheet rock and damage to the house," he said. "You are continuously waiting for the other shoe to drop. You're concerned that there is going to be another one."

What's shaking?

Since 2008, the northern region of Texas experienced four swarms of earthquakes, more 130 temblors in all.

Concentrated within the Dallas metro area, the frequency of this activity has dramatically increased this year. There were 25 small quakes in January alone.

Most are small, but for an area that the USGS says had only one recorded earthquake in the 58 years before 2008, the uptick has many in the community concerned.

Hough, who has studied seismic activity for years, says the shaking pattern "fits the mold of induced quakes."

To translate: the seismic activity could be a result of human activity, namely the disposal of a byproduct of hydraulic fracturing called "flowback water."

Officially, the cause of the earthquakes is inconclusive, according to the USGS, but on Tuesday, a Southern Methodist University-led research team found that in Azle and Reno, towns northwest of Fort Worth, the oil and gas activities in the vicinity were "most likely" responsible for several earthquakes in late 2013 and 2014.

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"While some uncertainties remain, it is unlikely that natural increases to tectonic stresses led to these events," head researcher Heather DeShon of SMU wrote in the report.

This findings were made possible by a "first-of-its-kind" modeling study that "allowed the SMU team to move beyond assessment of possible causes to the most likely cause identified in this report," it said.

This new data helps clarify the locations of the faults that are the sources of the earthquakes, SMU geophysicist Brian Stump said.

Stump echoed comments made by DeShon earlier this year, explaining that the pattern and position of many of the quakes form a linear trend.

"In order to have an earthquake with the size 3.6 magnitude, there has to be a fault," she said.

Stump and DeShon say they need more time to monitor activity and "explore the possible mechanisms for these earthquakes."

George Choy, a USGS research geophysicist, isn't ruling out that wastewater wells or the injection of fluid into the Earth's crust during fracking can cause the ground to shake, but he isn't ready to declare it a fact yet.

"There just isn't enough evidence to support the claim yet in this case," Choy said. "I don't think that has been proven yet. There are some nearby wells that have been inactive for a while. The connection has not been established, but we cannot rule them out. ... We cannot make a correlation with any wells without knowing their history."

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Researchers face challenges obtaining the information they need, Choy said, "since many of (the wells) are privately owned, digging into that history can often prove challenging."

The group that holds key details is the Texas Railroad Commission, which hired seismologist Craig Pearson in April 2014 to help it review well permits, analyze seismic data and assist SMU's DeShon and Stump.

In a statement to CNN, the commission said, "At this time, there is no definitive link between oil and gas activities in Texas and seismic events" and the commission "has taken numerous, proactive steps on this issue as research is developed in this area." The commission will continue to help researchers, local governments and industry to nail down information that may advance their studies, it said.

Wait and see?

While scientists argue whether fracking is the culprit behind the earthquakes, residents of Denton, a Dallas suburb, have taken matters into their own hands.

The Denton Drilling Awareness Group's mission is to educate the "public about the dangers of gas well drilling and its related processes to the public health, the environment, and property values."

The group's founder, registered nurse Cathy McMullen, told CNN she started the campaign after living next to a fracking well.

She and her husband thought their retirement plan was in full swing until their Decatur, Texas, ranch was surrounded by trucks preparing to excavate and drill for gas. She lost several cattle to a contaminated livestock water reservoir, which she believes was tainted by the nearby operation, she said.

Frustrated, the McMullens called the owners of the adjacent property, who sold the McMullens their land, and found out that although she and her husband had legally purchased their parcel, they did not own the rights to the minerals beneath the ground. The rights belonged to the original property owners, who had leased them to Aruba Petroleum, McMullen said.

One day, her husband noticed people hopping their fence and ran them off.

They were from Aruba Petroleum, she said, and the fence-hoppers later returned with the local sheriff, who told the McMullens that because the original land owners retained the rights to the subsurface minerals, they could not stop Aruba from digging on their own property.

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"That's just how it is in Texas," McMullen said, "Mineral rights supersede surface owners' rights."

She and her husband decided to move to Denton, where they expected a larger city to protect them from such intrusions. They were wrong.

Two weeks after moving to Denton, McMullen noticed "five stakes with pink flags on them" in a field near a park by their new home -- the telltale signs of gas wells soon to be dug, she said.

They were planning to put wells 300 feet from a park, McMullen said.

After one of the wells was dug, the McMullens started experiencing symptoms similar to what the Parr family, her former neighbors in Decatur, had complained of, including unforgiving "headaches and insomnia."

Aruba Petroleum had no comment, citing ongoing legal action. The company has appealed a 2014 decision in favor of the Parrs, which was billed as a first-of-its-kind fracking verdict

McMullen took her grievance to state officials, who told her if the city's ordinances had been stronger, the city could have stopped the wells.

In 2014, Denton voted to makes those ordinances stronger and become the first Texas city to approve a hydraulic fracturing ban.

"What we did is democracy, action, grassroots. It was hard work for people who live in this city and wanted a better life," McMullen told CNN.

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Denton City Councilman Kevin Roden, an early supporter of the ban, said, "The industry's lack of sensitivity to this issue and the inability of state law to allow the city to curb such behavior left our citizens in a state of desperation."

The day after the ban passed, Denton was sued not only by a fracking group, but also the state of Texas. Roden is confident Denton will win the legal fight but warns, "This is an uphill battle for the city given the political climate in our state."

What do scientists say?

The problem isn't solely the drilling, some scientists argue. It's the disposal of a wastewater byproduct of the drilling.

The way most companies dispose of this byproduct is to push it thousands of feet underground. The mixture of millions of gallons of water and potentially harmful chemicals are pumped into the earth's crust, and the liquid lubricates the faults, causing the earth to shake, or so the theory goes.

A key point in SMU's preliminary report is about the depth of these earthquakes, which have been 3 to 4 miles deep. This places most of them "in the shallow crystalline basement (granites) below the sedimentary rocks (sandstone, shale, limestone, etc.) that comprise the Fort Worth Basin."

An injection of wastewater that reaches the granite basement can agitate an existing -- or previously unknown -- branch of a large fault, resulting in the ground shaking.

Denton is not the only place that has banned fracking operations because of environmental concerns.

In Longmont, Colorado, residents voted two years ago to ban hydraulic fracturing. In Ohio, hydraulic fracturing has also been linked to an uptick in earthquakes.

After a string of small earthquakes, a magnitude-4.0 quake in late 2011 prompted Ohio Gov. John Kasich to issue a fracking moratorium in the vicinity of the activity. The Ohio legislature has also banned the practice in state parks and nature preserves but not in protected wildlife areas.

In New York, Gov. Andrew Cuomo has banned the practice in the entire state, citing public health concerns.

This exercise in democracy comes with a price. Many places are bracing for legal action from the energy sector, similar to what Denton has experienced.

The Department of Interior, which is responsible for oversight of public and Native American land where there are more than 100,000 oil and gas wells, recently announced new draft rules concerning hydraulic fracturing. The department received 1.5 million comments from the public on the matter over the past four years.

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Consulting with stakeholders from the energy industry, environmental experts and state and tribal regulators, they developed sweeping changes for well operators to be held to "higher standards for interim storage of recovered waste fluids from hydraulic fracturing to mitigate risks to air, water and wildlife."

The rules are intended to "protect public health and the environment during and after hydraulic fracturing operations at a modest cost, under the department's jurisdiction."

Residents in University Hills, Texas, are trying to take matters into their own hands, filing a petition asking Irving to bring in independent scientists to determine the cause of the recent quakes.

The petition says that even though these are not large earthquakes, they are "creating damage ... like foundation issues, pipe damage in slab foundations, cracks in the walls, floors, and ceilings, and a decrease of structural integrity."

Nell Anne Hunt is a real estate agent who has lived and worked in University Hills for more than 30 years and describes her experience as "extremely unsettling."

Many homeowners in her neighborhood are nervous about what this could do to their property values, she said, and they're scrambling to buy earthquake insurance.

Enough isn't being done to figure out the cause, she complained.

"I'm disappointed the city has been so passive. I wish somebody could get to the point of investigating what's going on," Hunt told CNN.

As he optimistically waits for answers, Jim Wells often thinks about a quote from one of his favorite movies: "Blade Runner," the science-fiction movie starring Harrison Ford.

"It's a terrible thing to live in fear," he said. "And that's kind of what we are in right here. We just don't know what's going to happen. Are the quakes going to get stronger? Are they going to become more frequent? We just don't know. "