It's more than just settling..it is very UN-Settling
2009–17 Oklahoma earthquake swarms
CAUSE:
Researchers have correlated the increase in earthquakes in central and north-central Oklahoma to injection disposal of produced water from two actively drilled stratigraphic intervals: the Mississippi Lime play, in north-central Oklahoma and extending into Kansas, which uses hydraulic fracturing; and the Hunton dewatering play, in central Oklahoma, which does not use hydraulic fracturing.[58] Both Mississippi Lime and Hunton plays produce large volumes of produced water; frac flowback makes up less than 5 percent of the injected wastewater.[59] More than 70 percent of the produced water from both plays is disposed through permitted Class II injection wells into the Arbuckle Group where it rests on Precambrian basement. The increase in pore pressure can release pre-existing stresses along faults in the basement rock.[60]
Between 2011 and 2014, the percentage of earthquakes spatiotemporally associated with injection wells has increased sharply by 87%.[61] A study of historic earthquakes has concluded that "much of the earthquake activity in the 1950s and 1980–1990s was induced" by injection of wastewater in deep disposal wells and the cluster of activity since 2009 is not consistent with the natural rate of fluctuations seen in the past.[
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