For residents in Oklahoma, thousands of tiny earthquakes in the past five years have mostly been annoying.
But a new study in Geophysical Research Letters suggests the future could be more dire, with the state possibly seeing larger temblors. It found that the same fault lines that have triggered earthquakes of between 3 and 4 magnitude are capable of producing events as high as 6 on the Richter scale.
The study, led by Dan McNamara, a research geophysicist at the U.S. Geological Survey, found that there were 3,639 earthquakes in Oklahoma between late 2009 and 2014, which was 300 times more than in previous decades. Several of these earthquakes caused damage and many were felt, with over 153,000 individual reports for 474 separate earthquakes entered at the USGS.
Many of those quakes occurred on average 3 miles underground along the Nemaha and Wilzetta fault zones, broad cracks in the Earth’s crust in central Oklahoma that were originally formed 300 million years ago during what was then called the Pennsylvanian period or the late Carboniferous period.
Until recently, the faults in Oklahoma had largely been quiet so the huge increase initially puzzled scientists.
Several studies have traced the increase of earthquakes in Oklahoma as well as Ohio to the oil and gas industry’s increased use of injection wells to bury huge amounts of wastewater underground. Resulting from enhanced hydrocarbon extraction operations, scientists believe the wastewater may increase the pressure on the rocks enough to cause seismic events.
A paper in Science last year concluded that four of the highest-volume disposal wells in Oklahoma are likely behind 20 percent of hundreds of quakes since 2008 east of the Rocky Mountains. And a 2013 study in the journal Geology concluded that a 2011 earthquake in the tiny remote town of Prague – a 5.6 magnitude temblor that was the largest in Oklahoma’s history – was due to the injection of wastewater underground.
It, along with several others above 4, resulted in more than a dozen homes destroyed.
“If a similar size earthquake were to occur in Oklahoma City or near Cushing oil facility, you can image there would be a lot more damage and higher costs,” said McNamara.
The study, which also identified several faults where earthquakes were occurring that had not been described before, will be used to develop a new earthquake-hazard map for Oklahoma that the USGS is planning to issue later this year. This will mark the first time the state’s earthquake hazard maps will include suspected human-induced earthquakes, which will “aid in adapting building codes to ensure that structures can withstand more damaging earthquakes.”
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SOURCE: CBS News, Michael Casey