The New Geophysics: a new understanding of fluid-rock deformation

Recent observations of stress-aligned shear-wave splitting (seismic-birefringence) show that the splitting is controlled by the stress-aligned fluid-saturated inter-granular microcracks and preferentially orientated pores pervasive in most in situ igneous, metamorphic, and sedimentary rocks in the earth's crust. These fluid saturated microcracks are the most compliant elements of the rock-mass and control rock deformation. The splitting shows that microcracks are so closely spaced that they verge on fracture-criticality and fracturing, and are critical systems with the butterfly wing's sensitivity. As a result, the evolution of such fluid-saturated rock can be modelled with anisotropic poro-elasticity (APE), so that behaviour can be monitored with shear-wave splitting, future behaviour calculated (predicted), and in principle future behaviour controlled by feed back. This is likely to have massive implications for virtually all solid-earth deformation at levels of stress below those at which fracturing takes place.