A study has been made of seismic measurements (VSP) from the deep Gravberg-1 borehole in the Siljan Ring area in central Sweden. The three-component data were processed with a focus on a known dolerite sill. The results show clear reflectivity for the compressional wave, indicating a reflection coefficient in the interval 0.05-0.07 for the granite-dolerite contact, which is lower than the simple interface value calculated from estimated velocities and densities. There is apparently little reflectivity for the shear wave, which might be explained by a high Vp/Vs-ratio for the dolerite.
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