Shear-wave splitting (seismic birefringence) shows that fluid-saturated microcracks throughout the Earth's crust are so closely-spaced they verge on fracturing and hence are critical-systems. Such criticality imposes fundamental new properties on conventional sub-critical geophysics that resolve several previously inexplicable geophysical anomalies as well as implying a New Geophysics that has implications and applications for almost all solid-earth processes and operations including particularly hydrocarbon-production, carbon-sequestration, and forecasting-earthquakes, as well as suggesting new techniques for investigating currently-important solid-earth processes. This review summarises this new understanding of fluid-rock deformation where the new properties include: monitorability, calculability, predictability, universality, and extreme sensitivity to initial conditions. These new properties suggest that New Geophysics is a fundamental advance in solid-earth geoscience.
Conventionally, in situ rocks in the uppermost half of the crust are considered to be brittle and elastically isotropic, except where heavily fractured rocks induce seismic anisotropy and cause shear-wave splitting. However, there are several unexplained anomalies:
Stress-aligned shear-wave splitting, indicating some form of anisotropy is almost universally observed throughout the Earth's crust and uppermost mantle;
The inability of oil companies, despite immense research investment, to extract more than an average of 30% to 40% of the oil in any reservoir.
Why in situ rock is so weak to shear-stress that the stress drops at earthquakes are typically 2 to 4MPa independent of the enormous range of the earthquake energy release.
We identify further anomalies below. Note that we are so accustomed to many of these anomalies that they are seldom questioned. They are merely accepted as the way in situ rocks behave, without appreciating the underlying dilemma that we cannot understand the mechanisms. We review evidence that pervasive distributions of stress-aligned fluid-saturated microcracks in almost all rocks in the crust are so closely-spaced they are critical-systems.