Mid-Continent Section

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Spatial analysis of selected earthquake clusters recorded by a dense network of seismic stations around Stillwater, Oklahoma


If the recent increase in seismicity in north-central Oklahoma is a result of the disposal of produced fluids into Underground Injection Control (UIC) Class II wells, earthquake distributions should directly demonstrate a spatial correlation. Oklahoma State University has deployed a dense network of broadband seismic stations in the immediate area of Stillwater, Oklahoma. We are using data from these stations along with data from OGS and USGS stations to locate micro-earthquakes that are generally below the threshold of detection for the regional seismic networks. Statistical spatial analysis of (micro-) earthquake locations with respect to UIC Class II injection wells will demonstrate the presence or the absence of a relationship. If the earthquakes are induced by UIC Class II injections, and depending on the availability of injection-well start-of-operation dates, volumes, and well-head pressures, it may be possible to track the spatio-temporal progression of a seismogenic pore-fluid pressure front from an injection well to preferentially-oriented faults along which greater-magnitude earthquakes occur or are likely to occur. Absent sufficiently current data on UIC Class II wells, the spatio-temporal evolution of clusters and linear trends will still provide the foundation for future analysis when the pertinent injection data become available. Whether the increase in seismicity in Oklahoma is natural or anthropogenic is potentially a serious public-safety issue.