The hydrostatic corer Selcore—a tool for sediment sampling and geophysical site characterization

Hydrostatic energy is used to power an active device for sediment sampling and geophysical site characterization. In the Selcore design, a steel tank with built-in drive unit constitutes the core head. The difference between ambient water pressure and atmospheric pressure in the tank provides the energy. The Selcore prototype enters the seabed as a gravity corer and automatically shifts into pile driving mode with up to 52 duty cycles without the need for an external trigger mechanism. The corer has operated in water depths from 300 to 3500 m. Operation at depths shallower than 300 m including on dry land can be facilitated using auxiliary water pressure. Penetration and recovery is generally more than two times the performance of a gravity corer of equivalent weight. The added utilization of hydrostatic energy has particular advantage in cases of relatively high shear strength sediments as well as attempts to core shallow bedrock below a sediment cover. Selcore has potential as a seabed seismic hammer source and initial land tests show good signal repeatability. Estimates of sediment thickness and seismic velocity obtained from the inversion and interpretation of the dominant Rayleigh surface waves corresponds closely to the shallow borehole stratigraphy at a land test site.