Is the Recent Increase in Seismicity in Southern Kansas Natural?
Abstract:Earthquakes in southern Kansas were nearly unheard of until September 2013, when two M2 earthquakes occurred. Since then, the earthquake rate has risen dramatically. Between December 2013 and July 28, 2014, 14 M≥3 earthquakes were recorded in Harper and Sumner counties, the largest being a M3.8 earthquake in December 2013. Residents of the towns of Caldwell and Anthony have reported feeling even more earthquakes. In response to the surge in earthquakes, the USGS deployed a 10-station seismic network to monitor earthquakes in southeastern Harper and southwestern Sumner counties. We have identified over 200 earthquakes that occurred from mid-June to late-July, 2014. The locations of these earthquakes cluster within or near the seismic array, ranging in magnitude from 0.5 to 3.5.
The earthquakes we identified are occurring within the Mississippian Lime Play, an area of rapidly expanding oil and gas development stretching from central Oklahoma to northwestern Kansas. In Kansas, new development of the play is largely in the adjoining areas of Harper and Sumner counties. Even with the new development, production in Sumner County has largely remained constant. However, in Harper County, where production was fairly stable from 1995-2010, it began increasing rapidly in 2011. In 2013 the highest yearly production volumes to date were approximately five times larger than those in 2010.
The spatial and temporal correlation of the oil and gas development and seismicity in southern Kansas suggests a potential relationship between the two; some of the earthquake clusters lie within 1-2 kilometers of recent development. We examine the possibility that the earthquakes in southern Kansas are induced by wastewater injection and/or hydraulic fracturing. This involves using a refined earthquake catalog built upon cross-correlation detections and high-precision earthquake relocation techniques. We also compute first-motion focal mechanisms and compare them to the regional stress field.