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Abstract. Velocities and Q values of P and S waves as functions of pressure and temperature (at 100 arid 600 MPa) are presented for a serpentinite and an amphibolite.Both rocks exhibit a strong lattice preferred orientation (LPO) of the major mineral phases antigorite and hornblende, respectively. Velocities and Q values increase with pressure; the rate of increase is different in the three orthogonal directions (normal and parallel to foliation and lineation) and closely related to progressive closure of microcracks. Increasing temperature decreases velocities and Q values only slightly as long as thermal cracking is prevented by the applied confining pressure. Substantial anisotropy of velocities and Q in P and S waves is observed in both rocks but is found to be different in origin. Anisotropy of P and S wave velocities is highest at low pressure and basically caused by constructive interference of effects related to oriented microcracks and to the LPO of major minerals. Increasing confining pressure decreases velocity anisotropy at a smaller and smaller rate. The residual anisotropy of P and S wave velocities (shear wave splitting) at high confining pressure is mainly a result of preferred mineral orientation. By contrast, anisotropy of Q is very low at low confining pressure and markedly enhanced as pressure is increased. At high confining pressure, substantial anisotropy of Q in P waves is apparent but reversed from that of P wave velocities' Q is highest in the direction normal to the foliation pl.ane P whereas Vp (and Vs) is lowest in this direction. The generation of a pronounced anisotropy of Qp by increasing pressure is due to a directionally dependent increase of contact areas on the oriented grain boundaries of the platy minerals defining the foliation. The increase of Q with pressure in the direction normal to foliation is mainly caused by the decrease of energy loss due to compressive strain relative to shear strain. The reverse is true for the X and Y directions (serpentinite) and X direction (amphibolite) parallel to the foliation plane.

Abstract. Combined gas permeability and P and $ wave velocity measurements were carried out on rock salt samples from the Gorleben salt dome and the Morsleben salt mine under hydrostatic and triaxial loading condions, mostly at room temperature. Permeabilities in the as-received samples vary between 10 46 and 2xl 0 '20 m 2. The initial permeability is primarily due to decompaction induced by drilling, core retrieval and sample preparation. Hydrostatic loading gives rise to a marked decrease of permeability and a coeval significant increase of P and $ wave velocities due to progressive closure of grain boundary cracks, tending to approach the in situ matrix permeability (< 10 '2ø m2). The pore space sensitivity of P and $ wave velocities is used to monitor the in situ state of the microstructure. Their reversals define the boundary in the state of stresses between dilatant and compactive domains (dilatancy boundary). Dilatancy during triaxial deformation of the compacted rock salt samples is found to evolve stress dependent in various stages. The crack initiation stress increases from -•18 MPa differential stress at 10 MPa confining pressure to -•30 MPa at confining pressures above-•70 MPa. Dilatancy is due to the opening of grain boundary and (100) cleavage cracks and depends on the applied confining pressure. The orientation of the open cracks is primarily controlled by the loading geometry system (compression, extension). As a consequence, permeability increases dramatically with progressive dilatancy, followed by a period of plus/minus constant permeability during strain hardening up to 10% axial strain or even more. This suggests that the evolution of permeability is not only a function of dilatancy but also of microcrack linkage. Importantly, the anisotropic crack array within the samples causes a strong directional dependence of permeability.

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