A new study has revealed possible and previously unknown sources of earthquakes in Oklahoma, the U.S. Geological Survey and Oklahoma Geological Survey reported Friday.
Using magnetic measurements made during low-altitude airplane flights, both surveys say it may have revealed deep faults that may contribute to the increased seismic activity in response to wastewater injections in certain parts of the state.
The deep-imaging magnetic survey was data and results from August to October 2017.
The magnetic field maps revealed boundaries or contacts between different rock types, some of which are linear, similar to faults and align with sequences of earthquakes. This suggests that some of them represent faults that have been reactivated due to waster injection, which generates, or "induces" earthquakes, the U.S. Geological Survey reported.
The data show there is a dominant “grain” direction to the magnetic contacts (like wood grain) in the deep rocks where the earthquakes are occurring. This “grain” was formed hundreds of millions of years ago and may be composed in part by faults that are oriented favorably to move in response to natural background stresses within the earth. This alignment of deep features may contribute to the high levels of seismicity occurring in response to wastewater injection.
The surveys used newly acquired airborne magnetic data to image rocks where the earthquakes were occurring miles beneath the surface due to only a few earthquake sequences happening on mapped faults, making seismic hazards difficult to estimate.
The U.S. Geological Survey said thousands of earthquakes in Oklahoma are associated with wastewater injection activity.