Seismologists installed a new earthquake-monitoring device in the Dallas suburb of Irving this week after a series of minor tremblors rocked an area near the site of the former Dallas Cowboys football stadium.

Irving was shaken by nine quakes on Tuesday and into Wednesday, including three measuring magnitude 3.6, 3.5, and 3.1, the U.S. Geological Survey said. The quakes were the strongest in a series of about 20 minor quakes to hit around the stadium area since September.

Five smaller quakes registering between 1.6 and 2.9 were recorded on Tuesday in the suburb. Another 1.7 magnitude quake was recorded in the nearby city of Farmers Branch late on Tuesday night, according to the USGS.

There were no immediate reports of injury or damage.

But the seismic series has left residents on edge, wondering whether the situation will get worse and what has been behind an uptick in quakes over the last several years.

"The safety and security of our residents is paramount for the city of Irving," said Irving City Manager Chris Hillman.

Some residents believe the implosion of Texas Stadium in 2010 may have exacerbated problems. There is also speculation the quakes might be related to hydraulic fracturing, or "fracking," an energy extraction technique that has a long history in north Texas.

Irving, headquarters of Exxon Mobil's XTO unit that helped pioneer hydraulic fracturing in the region, has two gas wells that were fracked in 2010, according to city officials.

The study by seismologists from Southern Methodist University in Dallas is aimed at pinpointing the quakes' epicenters, said SMU seismology professor Brian Stump.

About 40 miles west of Irving, a series of small earthquakes rattled the town of Azle a year ago, causing sinkholes and cracks in house foundations. Residents blamed fracking and injection disposal wells for drilling waste as the cause, but an official finding is still pending.

Energy industry officials have said fracking is safe and causes no significant seismic damage.