RELATIONSHIPS BETWEEN PRE-EXITING STRUCTURE, REGIONAL STRESS ORIENTATION, AND SEISMICITY INDUCED BY WASTEWATER INJECTION, NORTHERN APPALACHIAN BASIN, USA

Recent seismicity in the northern Appalachian Basin has been attributed to active wastewater injection operations. Current models of induced seismicity suggest that movement along pre-existing faults/fractures with orientations optimal to the regional maximum horizontal stress field is the likely source of recorded earthquakes. As part of this investigation, we evaluated the relationships between injection wells, waveform template matching-derived locations of induced earthquakes, and subsurface structures mapped using data from over 600 wells in Ohio and West Virginia. We also evaluated subsurface in-situ stress conditions determined from regional studies and local hydraulic fracturing operations to evaluate the principle stress orientations/magnitudes for comparison with the trends of identified earthquake epicenters.

Study results indicate that the locations of seismic events likely induced by wastewater injection operation in Washington County, Ohio correspond to the trend of small-amplitude folds in Upper Devonian rocks close to injection well locations. Similar amplitude folds imaged in nearby seismic reflection lines are associated with basement-involved fault systems that cut the injection interval, providing a possible permeability pathway for fluid pressure increases that could initiate slip. While subsurface mapping in other parts of the basin have not yielded similar structural/epicentral relationships, the orientation of induced events throughout eastern Ohio correspond to the predicted optimal orientation of reactivated fault/fracture zones given the regional principle stress directions.