REGIONAL EVALUATION OF FAULTS IN PALEOZOIC BEDROCK AND THEIR POTENTIAL FOR INDUCED SEISMICITY IN EASTERN OHIO

Publically available oil and gas well data has been used to generate structure contour and isopach maps of upper Paleozoic strata in eastern Ohio in order to evaluate structural trends that could be related to shallow faults. World Stress Map results for eastern Ohio and adjacent areas indicate subvertical σ₂ with the maximum horizontal stress oriented between 060 and 096, and with the highest quality results clustering between 060 and 070. Mechanical analysis under this stress regime suggests that steeply dipping faults with azimuths of 040 +/- 15 or 090 +/- 15 are likely near failure under hydrostatic conditions. We identify an area of particular concern in southeastern Ohio near the Ohio River between New Martinsville, West Virginia and Marietta, Ohio. The unusually linear trend of the Ohio River in this area suggests that it follows a zone of weakness nearly 40 miles long and trending ~047 that closely follows an inferred basement fault at depth corresponding to the northwest flank of the Rome Trough. Moreover, isopach and structure contour trends at stratigraphic levels as high as the Mississippian Berea Sandstone suggest that this trend acted as a subvertical zone of recurrent structural disturbance throughout the Paleozoic. The relatively large extent of the inferred structure and the recent occurrence of minor seismicity in the vicinity of several deep wastewater injection wells in eastern Washington County raises concern that increasing volumes of wastewater injection associated with increased hydraulic fracturing activity in the area of interest could lead to enhanced risk of significant induced seismicity along the intensely industrialized Ohio River corridor. However, reconnaissance observation of Late Pleistocene to Holocene sediments in this area revealed no evidence of major Holocene seismic disruption. Nevertheless, this segment of the Ohio River may merit a cautious approach as more extensive hydraulic fracturing moves into the area with attendant needs for greater deep wastewater injection.