DALLAS (AP) - A cluster of small earthquakes rattled a Dallas suburb for a second day Wednesday as experts turned to seismic data to help determine why.
The temblors in the Irving area included three quakes Wednesday morning, the U.S. Geological Survey reported.
Irving police had no reports of injuries or major damage in the 11 earthquakes that hit the area since Tuesday, but asked the public to stop calling 911 to report the shaking unless someone was hurt or there was another emergency.
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.
Small earthquakes have become more common in Texas and Oklahoma. In October, Texas officials amended rules for disposal well operators amid concerns that high-pressure injections related to hydraulic fracturing, or fracking, can trigger earthquakes.
Carrieann Bedwell, a geophysicist with the USGS in Golden, Colorado, said scientists would be investigating.
"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.