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By Anna Kuchmen
Science Writer

Earthquakes beneath DFW International Airport continued for seven years after an oil and gas company shut a nearby wastewater injection well that had been linked to the quakes, according to a new study by scientists at 91��Ƭ�S�ϼ�.

A wastewater well that continues to operate at the northern end of the airport — and which some area residents have said should be closed — was probably not involved in the events and poses little earthquake hazard, the researchers concluded.

“Faults are not like a light switch - you don’t turn off a well and automatically stop triggering earthquakes,” said Heather DeShon, a seismologist at 91��Ƭ�S�ϼ� and co-author of the paper, in an email.

The earthquakes at DFW Airport started on Halloween 2008, seven weeks after Chesapeake Energy began injecting wastewater  into a well at the southern end of the airport. Scientists at SMU and the University of Texas at Austin investigated the quakes at the time and concluded they were most likely associated with the well.

Though Chesapeake shut its well in August 2009, earthquakes continued through at least the end of 2015. The largest, a 3.4-magnitude event, struck three years after the well was closed.

“It’s very surprising that one year of injection could produce earthquakes running for more than seven years,” said Paul Ogwari, the study’s lead author and a post-doctoral researcher at SMU. The paper was published in the .

While earthquake magnitudes did not decline, Ogwari said, earthquake rates did: More than 80 percent of quakes in the sequence occurred during the first seven months of seismicity.

The DFW quakes are significant, because they mark the start of an unprecedented surge of earthquakes in North Texas and across the middle of the country. Since 2008, at least five North Texas cities and towns — Cleburne, Azle, Venus, Irving and Dallas — have felt clusters of quakes, most of which have been small and caused little damage.

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