Oil and gas activities may have caused nearly nine in 10 of the earthquakes Texas has experienced in the past 40 years, and the quakes have become more frequent as oilfield activity has picked up in the past decade, according to a forthcoming study.

Of the 162 Texas earthquakes of magnitude 3 or greater between 1975 and 2015, a quarter were “almost certainly” induced by oil and gas activities, while 33 percent were “probably induced and 28 percent were “possibly induced,” researchers led by University of Texas-Austin geoscientist Cliff Frohlich wrote.

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