EPISODIC REACTIVATION OF CRITICALLY-STRESSED BASEMENT FAULTS IN SOUTHERN KANSAS: IMPLICATIONS FOR WASTEWATER DISPOSAL AND LONG-TERM STORAGE OF CO2

Kansas resides within the stable craton, a characterization that contrasts it with tectonically active portions of the U.S. However, the Proterozoic basement beneath Kansas contains a number of well-defined discontinuities or lineaments, many of which are faults with large offsets that show evidence of reactivation within shallower stratigraphy. Although the role of these faults within the current stress regime is not clear, a growing number of researchers argue that the midcontinent crust is critically-stressed and that injecting large volumes of fluid (waste-water or CO₂) poses a high risk for induced seismicity and fluid leakage. The recent uptick in the frequency and size of earthquakes in the southern part of the state has elevated these concerns, but poor knowledge of subsurface faults and their relationship with regional stresses are major obstacles to evaluating the cause of the seismicity and to developing possible mitigating strategies. To address these issues on a broad scale, we use a dense sampling of stratigraphic tops, determined from publicly-available well-log data, to construct structure contour maps of 18 regional stratigraphic surfaces. We use a range of surface analysis techniques (e.g., slope, curvature, and residual analysis) combined with thickness variations, determined from isopach maps, to identify potential faults. To evaluate the consistency of the mapped faults, we will compare them to documented surface lineaments and discontinuities determined from analysis of state-wide potential field data. To identify the faults most favorably oriented with respect to in situ stresses and thus, those with the highest potential for reactivation, we will analyze borehole breakouts, drilling-induced fractures, and drilling-enhanced fractures from available well logs (e.g., 4-arm caliper and image logs), which will provide the orientations of the minimum and maximum horizontal stresses. The resulting fault map will identify high and low risk subsurface faults, and ideally provide regional stakeholders some context for recent and future seismic events.