Time dependent strain recovery of cores from the KTB — Deep drill hole

Summary

The time dependent strain recovery is investigated for drill cores of two rock types from the German Continental Deep Drilling Project (KTB). The strains are measured with inductive displacement transducers in the core axis and in three different radial directions under constant conditions of temperature and moisture. It turns out that the process of time dependent strain recovery is closely connected with the emission of acoustic signals. A non-foliated, fine grained lamprophyre (depth: 2231.50 m) and a strongly foliated gneiss (depth: 2415.90 m) show a distinctly different relaxation behaviour. The relaxation times for both, deformation and acoustic emissions, are approximately the same and 57 hours for the lamprophyre and 28 hours for the gneiss. In the case of the viscoelastically isotropic lamprophyre principal in situ stresses have been calculated.