DALLAS (AP) Nine small earthquakes rattled a Dallas suburb in less than 24 hours and experts Wednesday turned to seismic data to help determine why.

The temblors in the Irving area including a 3.1 magnitude quake before dawn Wednesday, the U.S. Geological Survey.

Irving police had no reports of injuries or major damage in the earthquakes that began around 7:30 a.m. Tuesday. The magnitudes ranged from 1.6 to 3.6, according to the USGS.

Earthquakes of magnitude 2.5 to 3.0 are generally the smallest felt by humans, experts say.

Carrieann Bedwell, a geophysicist with the USGS in Golden, Colorado, said senior scientists would be investigating the temblors.

"They will be looking at the parameters, magnitude, depth, location of each of the events," Bedwell said Wednesday. "Right now we're calling it a swarm, because we've had multitude events happen."

Bedwell described a swarm as earthquakes approximately in the same location in a matter of a few days or so.

"Earthquakes of this size, like 2s, 3s, can happen pretty much anywhere in the world at any time," Bedwell said.

The Irving area, with a population topping 250,000, has had more than 25 minor earthquakes since early September, according to Brian Stump, a seismologist with Southern Methodist University.

"SMU's seismology team is committed to helping North Texans understand more about the increasing number of earthquakes felt in our region over the last few years, most recently near the city of Irving," Stump said in a statement Tuesday.

SMU researchers installed a seismometer in Irving on Monday. Other devices were set up earlier near Dallas-Fort Worth International Airport and on the Dallas campus.

Separately, the USGS reported a 3.5 magnitude earthquake Tuesday afternoon near Snyder, about 250 miles west of Irving.