The U.S. Geological Survey has confirmed that four low-magnitude earthquakes have taken place over the past two weeks in the Eagle Ford Shale of South Texas.
USGS officials confirmed a 2.5-magnitude earthquake about five miles east of the Gonzales County town of Smiley on Saturday evening.
No major damages or injuries were reported from the low-magnitude earthquake, which followed a 3.1-magnitude earthquake was recorded less than mile northwest of Smiley five days before.
Another 3.1-magnitude earthquake was recorded a couple miles south of Westhoff in neighboring DeWitt County on May 12.
One day earlier, USGS officials recorded a 3.0-magnitude earthquake a few miles east of the Karnes County town of Gillett.
There have been seven earthquakes recorded in the Eagle Ford Shale of South Texas this year.
Environmentalists blame the tremors on saltwater disposal wells, which inject wastewater generated in the hydraulic fracturing process and other oil and natural gas activities deep underground.
Saltwater disposal wells are regulated by the Railroad Commission of Texas, the state agency that regulates the oil and natural gas industry.
Railroad Commission officials adopted stricter regulations for saltwater disposal wells in November 2014. Over the last four years, the agency received 367 disposal well applications in areas of historic seismicity.
Of those proposed projects, 163 permits were issued with special conditions that include reducing maximum daily injection volumes and pressures as well as being required to record volumes and pressures on a daily basis as opposed to monthly.
Fifty-four disposal applications were returned or withdrawn. Eleven applications were sent to hearing. Twenty-one permits were issued without special conditions and 118 applications are pending technical review.