On the pressure dependence of elastic parameters in porous and fractured rocks of the upper continental crust

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Within the ICDP-Program "Energy and Fluid Transport in Continental Fracture Systems" this project is dedicated to the stress and fluid pressure dependency of anisotropic elastic parameters in the continental upper crust. Our project follows two aspects: a) the extension of the piezosensitivity approach towards fractured anisotropic media including effects of nonlinear elasticity and (b) its application to laboratory data from KTB core samples. This approach establishes a set of equations which allow to interpret velocity vs. pressure data in terms of compressibility and porosity of porous and fractured fluid saturated rocks. It is one of the very few theoretical approaches allowing a direct interpretation of the stress dependency of seismic velocities in terms of rock physical parameters. Furthermore, it introduces additional and to some extend new rock characteristics, like the piezosensitivity and stiff and compliant porosity. Measurements of anisotropic elastic velocities and bulk deformation over a differential pressure range up to 350 MPa and higher are available for a set of 136 core samples from the KTB deep laboratory. These data will be analyzed and reinterpreted in terms of the anisotropic piezosensitivity approach. This will give a closer insight into the stress dependent elastic anisotropy of the KTB rocks under the in situ tensorial state of stress. It might help to explain observed and to predict possible anisotropy changes due to changes of pore fluid pressure in the rocks of the upper continental crust.