1. British Geological Survey, Edinburgh EH9 3LA, Scotland UK.
2. School of GeoSciences, University of Edinburgh, Edinburgh EH9 3FW, Scotland UK.
3. Institute of Earthquake Science, China Earthquake Administration, Beijing 100036, China.
Abstract We identify two interrelated but independent species of microcracks with different origins and different distributions. One species is the classic high-stress microcracks identified in laboratory stress-cells associated with acoustic emissions as microcracks open with increasing stress. The other species is the low-stress distributions of closely-spaced stress-aligned fluid-saturated microcracks that observations of shear-wave splitting (SWS) demonstrate pervade almost all in situ rocks in the upper crust, the lower crust, and the uppermost 400 km of the mantle. On some occasions these two sets of microcracks may be interrelated and similar (hence ‘species’) but they typically have fundamentally-different properties, different distributions, and different implications. The importance for hydrocarbon exploration and recovery is that SWS in hydrocarbon reservoirs monitors crack alignments and preferred directions of fluid-flow. The importance for earthquake seismology is that SWS above small earthquakes monitors the effects of increasing stress on the pervasive low-stress microcrack distributions so that stress-accumulation before, possibly distant, earthquakes can be recognised and impending earthquakes stress-forecast.
This study was partially supported by the National Natural Science Foundation of China (No. 41174042).
Cite this article:
Stuart Crampin,GAO Yuan. Two species of microcrack[J]. APPLIED GEOPHYSICS, 2014, 11(1): 1-8.
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2014, Vol. 11 
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