FORT WORTH, TX (KTRK) -- The risk of an earthquake in the flatlands of North Texas may be rising, the chief of the U.S. Geological Survey's National Seismic Hazard Project says.
After more than 120 earthquakes since 2008, USGS will likely upgrade the risk of an earthquake occurring in the Dallas-Fort Worth area, though not by much, Mark Petersen told the Dallas Morning News.
For the first time this year, the agency will include quakes believed to be caused by human activity in its National Seismic Hazard Map.
Though the study is ongoing, Southern Methodist University seismologists have linked two local earthquake clusters with wastewater injection wells, where companies dispose of chemical-laced fluids used in the hydraulic fracturing process. One cluster began in 2008 near Dallas-Fort Worth International Airport. The second occurred near Cleburne in 2009.
Researchers are investigating two more recent clusters: one in Azle and another in Irving, where the tremors continued Sunday.
Irving has experienced 35 small earthquakes in the last 12 months. 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. Though more damaging earthquakes are unlikely, scientists consider them possible.
USGS scientists are developing new tools to study induced seismicity, or manmade earthquakes.
"It's very difficult to assess where induced seismicity might occur," Petersen said. "They're based on economic and policy decisions which are difficult to forecast, especially over a 50-year time period."
The increase in earthquakes in Oklahoma and Kansas, among other states, is changing the way seismologists think about earthquakes. Between 2010 and 2013, people living in the central and eastern U.S. felt five times as many quakes per year, on average, as they did between 1970 and 2000, the newspaper reported.
"We're putting a lot of effort into understanding this," Petersen said.
The Associated Press contributed to this report
USGS will likely upgrade earthquake risk in North Texas