Integrating 3D VSP in Hard‑Rock Site Selection Strategies for Deep Geological Repositories

Summary This contribution presents a borehole centered 3D vertical seismic profiling (3D VSP) workflow tailored for crystalline host rocks in deep geological repositories. It addresses the key challenge of resolving brittle ductile deformation zones and fracture networks that control groundwater flow, site suitability and repository layout. The method combines dense multi offset, multi azimuth 3C acquisitions in deep boreholes with tomographic velocity modelling and Image Point (IP) migration, producing high resolution 3D structural images to cover the area of interest. These images are systematically integrated with core logging, borehole imaging and hydraulic testing to refine the structural and hydrogeological framework that underpins siting decisions and safety case analyses. Case histories from Finland (Olkiluoto/ONKALO) and Sweden, as well as a recent Canadian application, demonstrate that high resolution 3D VSP can reliably predict major water conducting zones ahead of excavation and materially reduce uncertainty on the continuity of sparsely intersected structures. We distil practical lessons on survey design, scale, integration and regulatory expectations, providing concrete guidance for emerging repository programmes seeking to integrate high resolution borehole seismics in their site selection and characterization strategies.