Earth & Environmental Sciences

We provide direct observations of the three-dimensional displacements of a fluid-driven fracture during water injections in a borehole at ∼1.5 km depth in the crystalline rock at the Sanford Underground Research Facility (USA). Micro-shearing of the borehole initiates on a foliation plane at 61% of the minimum principal stress σ3. As the fluid pressure increases further up to 112% of σ3, borehole axial and radial displacements increase with injection time highlighting the opening and sliding of a new hydrofracture growing ∼10 m away from the borehole, in accordance with the ambient normal stress regime and in alignment with the microseismicity. Our study reveals how important it is to consider monitoring zonal deformation in conjunction with pressure and flow to better manage the complex hydromechanical evolution of the growing fracture.