Two species of microcracks

两种类型微裂隙(英文)

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.

We identify two interrelated but independent species of microcracks with differentorigins and different distributions. One species is the classic high-stress microcracksidentified in laboratory stress-cells associated with acoustic emissions as microcracks openwith increasing stress. The other species is the low-stress distributions of closely-spacedstress-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 theuppermost 400 km of the mantle. On some occasions these two sets of microcracks may beinterrelated and similar （hence ＇species＇） but they typically have fundamentally-differentproperties, different distributions, and different implications. The importance for hydrocarbonexploration and recovery is that SWS in hydrocarbon reservoirs monitors crack alignmentsand preferred directions of fluid-flow. The importance for earthquake seismology is that SWSabove small earthquakes monitors the effects of increasing stress on the pervasive low-stressmicrocrack distributions so that stress-accumulation before, possibly distant, earthquakes canbe recognised and impendin~ earthquakes stress-forecast.