Oklahoma Yin Yang
With 2016 coming to a close, GG thought we might want to see just how things are shaking out in Oklahoma, home of the great induced earthquake experiment. And there is something for everybody, depending on how you want to look at it.
For the optimists hoping that Oklahoma’s actions to slow wastewater injection will end the plague of induced earthquakes, we have plot number one: number of quakes with a magnitude of 3.0 or higher by month:
The rate of such earthquakes dropped from nearly 4 a day in January to about one a day this month. And you could hope that this had something to do with this:
The 25% reduction during the year in the rate of injection in the area where triggered seismicity has been observed might be responsible for this. But there are other things to watch as well. First, these are still pretty high volumes of water going back into the Arbuckle, and all the water that went down earlier is still making its way through the subsurface. Second, presumably a lot of produced water is going to other wells, either in the Arbuckle outside the area of interest or into other formations. Third, a decrease in the number of M3+ events is not the same thing as a decline in seismic moment:
The 9/3/2016 M5.8 Pawnee, Oklahoma earthquake put a big damper on any celebration of a decrease in seismicity. The overall moment release of 7.8 x 1024 dyne cm is the largest single year moment release in Oklahoma history. As we noted before, this isn’t unexpected: the Rocky Mountain Arsenal sequence in the 1960s produced its largest quakes after the injection ended.
So we enter 2017 on a note of caution. If you bought earthquake insurance in Oklahoma, don’t let it lapse just yet. You might get shaken a bit less often, but when you do get a quake, it might still be pretty big.
P.S.: there are a couple of nice visualizations out there. Tulsa World put together an interactive map a year ago showing how produced water injection was varying over time and by county. The Oklahoma state government has an interactive figure with recent earthquakes and disposal well locations.