Comparative Study of Crosshole Seismic Reflection and VSP Imaging

The application of conventional surface seismic methods for mineral exploration is often challenged by environmental factors such as rough terrain and thick vegetation cover. To image deep-seated vertical structures by conventional surface and VSP methods requires considerable horizontal offsets and surface sources are often degraded by highly attenuating regolith. The Crosshole Seismic Reflection (CSR) method in conjunction with Kirchhoff migration is an alternative higher resolution seismic imaging method in such challenging situations. Using a simplified model of magmatic nickel sulphide mineralization in the Kambalda region of Western Australia, the CSR imaging method has been evaluated by comparing migration images with those of multiple-offset VSP (MVSP). Kirchhoff VSP migration was adapted to create Pre-stack Depth Migrated images outside of the inter-borehole space. High resolution images of the ultramafic-basalt contact and a steeply dipping fault were obtained in both methods. Because of the large surface source aperture, the MVSP geometry provided greater coverage of the ultramafic-basalt. However, the CSR geometry provides similar coverage with a higher fidelity image and greater depth imaging. Our case study show that the CSR method serves as a suitable alternative to conventional surface seismic and VSP where there are surface mobility restrictions.