Stress directions in eastern North America determined to 4.5 km from borehole elongation measurements

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Abstract
Stress directions have been determined to depths of 4.5 km in eastern North America from borehole elongation measured by dipmeter calipers in 47 wells. The average maximum horizontal stress directions are eastern Canada, N54°E ± 7°; Appalachian Basin, N58°E ± 8°; and the Illinois Basin, N89°W ± 5°. Stress directions determined for the Illinois and Appalachian basins are in agreement with published interpretations from hydraulic fractures and earthquake fault plane solutions. New results from eastern Canada and the Appalachian Basin show that stress directions are everywhere consistent with the Midcontinent stress province. These data suggest that the maximum horizontal stress does not rotate from the ENE Midcontinent trend to NW near the Atlantic coast. A directional analysis of hydraulic fractures, petal‐centerline fractures, and natural fractures from the Appalachian Basin shows that borehole elongation is systematically aligned perpendicular to the directions of hydraulic fractures, centerline fractures, and northeast striking natural fractures but is not systematically aligned with northwest striking natural fractures. These observations indicate that borehole elongations provide reliable stress orientations.