A week of earthquakes in Texas, Oklahoma

It was a week of earthquakes in Texas and Oklahoma.

In the Dallas-Irving area, three minor earthquake were detected on Thursday.

The U.S. Geological Survey reported a 3.3 magnitude quake happened at 5:36 p.m. CDT Thursday. The quake was centered in the Las Colinas section of northeastern Irving near Texas 114.

Police in Irving had no immediate reports of damage or anyone hurt in the earthquake.

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Seismologists have said that dozens of small quakes rattling North Texas in recent months were concentrated along a narrow two-mile subsurface fault. Experts from Southern Methodist University weeks ago placed more than 20 monitors around the quake sites and then determined the fault existed.

The Irving earthquakes that began earlier this year are the latest in a series of four clusters in the North Texas area since 2008. The first group hit near Dallas/Fort Worth International Airport between October 2008, and May 2009. That was followed by quakes in Cleburne between June 2009 and June 2010 and a third series in the Reno-Azle area between November 2013 and January 2014.

SMU seismologists say more than 120 earthquakes have been reported in the North Texas area

One significant change in drilling practices is contemporaneous with the increase in seismic activity: horizontal hydraulic fracturing. Fracking has been around for decades, but technological advances have allowed companies to drill sideways, injecting a high-pressure mix of water, mud, and sand into shale formations deep underground, creating access to previously unreachable pockets of oil and gas. Oil production in Oklahoma has more than doubled over the past decade, creating new wealth for the state as well as an unwanted surplus. Horizontal wells can produce as much as nine or 10 barrels of salty, toxin-laced water for every barrel of oil. Much of that fluid is injected back underground into wastewater disposal wells. It’s this water, injected near faults, that many seismologists-including those at the U.S. Geological Survey-point to as a factor in the spike in earthquakes.

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But there are other quakes being felt in other areas near where drilling is taking place.

More than a dozen small to moderate earthquakes were recorded in Oklahoma since Friday, including one with a preliminary magnitude of 4.2 that was felt in Kansas and Texas.

The U.S. Geological Survey reports the quake occurred at 8:21 a.m. Saturday 12 miles north of Crescent, about 45 miles north of Oklahoma City. Residents about 270 miles north in Topeka, Kansas, and about 240 miles south in Dallas reported feeling the quake.

Logan County Sheriff’s Sgt. Greg Valencia says there are no reports of damage or injury.

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The earthquakes began shortly before 4 p.m. Friday and ranged from a magnitude 2.7 to the 4.2, with at least two recorded at magnitude 3.7.

Geologists say damage is not likely in earthquakes below magnitude 4.0. Last year, Oklahoma had 585 earthquakes with a magnitude 3.0 or greater — almost three times as many as California had and up from an average of just two a year before 2009.

West Texas recorded a 3.3 magnitude earthquake.

The U.S. Geological Survey says the 3.3 magnitude quake occurred at 7:16 p.m. CDT Friday in Reeves County.

Experts say the earthquake was centered about 23 miles southeast of Pecos.

The Reeves County Sheriff’s Office on Saturday had no reports of any injuries or damage.