Oklahoma study reveals possible, previously unknown sources of earthquakes

This U.S. Geological Survey Map shows areas affected by earthquakes from fracking. (U.S. Geologial Survey)

The US Geological Survey and the Oklahoma Geological Survey used airborne magnetic data and magnetic field maps to determine possible deep faults that may contribute to increased seismic activity in response to wastewater injection in certain parts of Oklahoma.

Oklahoma has been the site of thousands of earthquakes associated with wastewater injection activity, or induced recurrent earthquakes, but few of the earthquake sequences have occurred on mapped faults, or known cracks in the earth's crust, making seismic hazards difficult to estimate.

"We are hoping the results will be used to guide more detailed studies at local scales to assess possible earthquake hazards," said USGS scientist Anji Shah, lead author for the study.

The data show that there is a dominant "grain" direction to the magnetic contacts, like wood grain, in the deep rocks where the earthquakes are occurring.

The "grain" was formed hundreds of millions of years ago and may be composed of faults that are sensitive to background stresses. It's possible this alignment is why the earthquakes are occurring so frequently in response to wastewater injection.

"There is nothing like a new data set to excite geoscientists looking for answers to some of the mysteries of induced seismicity in Oklahoma," said Dr. Jeremy Boak, OGS Director. "We look froward to discussing these results among ourselves and with the interested technical community. We also hope to bring these data to bear on addressing the persistent seismic activity and sharing our interpretations with Oklahomans and other stakeholders regarding this challenging issue."

Survey areas included parts of Alfalfa, Beckham, Comanche, Greer, Harmon, Kiowa, Jackson, Lincoln, Logan, Major, Noble, Pawnee, Payne, Pottawatomie, Stephens, Tillman, Woods and Woodward counties.

In 2017, the USGS stated that Oklahoma's earthquake threat now equals that of California, possibly as a result of the increase in wastewater injection wells.

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