13 February 2016 | Revised Quake Insights
The foreshock has been removed from the catalog, so perhaps this was a phantom event.
Five hours after the mainshock, improved earthquake depths and locations, as well as five aftershocks, have altered and enhanced the picture of what is likely induced seismic burst associated with deep injection of produced water.
The various depth determinations of the mainshock are now consistently about 8 km (5 mi), substantially deeper the bottom of any re-injection well. This would mean that fluids would need to migrate downward under injection pressures to trigger the mainshock. In addition, a M=3.9 aftershock now locates to the southeast of the mainshock, along a trend of quakes that struck during the preceding month. The relative location of the largest events, combined with the focal mechanism, might suggest a northwest-striking right-lateral fault with a length of at least 6 km and a width (the down-dip dimension) of at least 8 km. Such a fault is capable, in principle, of hosting a M=6.0 earthquake.
The largest quake to strike Oklahoma since 1980 is a M=5.6 shock 60 km (40 mi) east of Oklahoma City on 5 November 2011.
Ross Stein and Volkan Sevilgen
Data from USGS, and Oklahoma Geological Survey