Background

3D underground seismics enables high-resolution structural exploration of the subsurface in the near and far field. We have developed a modular seismic system that can be flexibly adapted to the specific conditions of underground environments. This technology provides valuable information for the extraction of raw materials, environmental studies, and geological research. We use active seismic measurements and monitoring to investigate the surroundings of various geological formations and potentially hazardous areas. Engineers and geophysicists work together on an interdisciplinary basis to develop seismic sources, receiver systems, and software modules specially optimised for underground applications. Our aim is to improve data acquisition, minimise noise signals, and achieve a comprehensive understanding of subsurface structures in crystalline, salt, and clay rock.

Applications of 3D Underground Seismics

• Tunnel exploration and forecasting
• 3D exploration of deposits
• Borehole environment investigations

Various imaging techniques, such as 3-component Kirchhoff migration or Fresnel volume migration, are tested and modified to evaluate their ability to resolve small-scale structures. The major challenge in underground seismic imaging is the spatial ambiguity of the recorded wave field due to the limited aperture of seismic source and receiver geometry. New imaging methods are being developed to improve the spatial resolution of structural objects. Therefore, the measured polarisation direction of the three-component data is used to determine reflection points and to restrict the migration operator to the area that physically contributes to a reflection event (Fresnel volume limit). As a result, migration artefacts and crosstalk effects of converted waves can be reduced compared to standard migration schemes. The imaging quality achieved is determined by considering the number of excitation and receiver points as well as the maximum aperture angle for each 3D image point.

Key Scientific Questions

• How can a modular seismic system be specially adapted to underground conditions?
• How can underground measurement geometries be optimised for specific target sizes and distances while considering existing and accessible cavities?
• What are the challenges of underground seismic imaging and how can new imaging methods address them?
• To what extent do imaging techniques such as Fresnel volume migration improve spatial resolution and reduce migration artefacts?