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The presence of polyhedral sub-particles in dynamically-formed shear zones in quartzite is a specific
manifestation of a very complicated and still enigmatic mechanism of shear fracture development. The
existence of these sub-particles allows disclosure of one important feature of this mechanism.
Comprehensive analysis of the geometrical shape of the sub-particles gave reason to conclude that the most
plausible explanation of their formation is shock unloading taking place in the fracture zone. At the same
time the fact that a relatively minute and very strong quartz grain can be disrupted into elemental sub-
particles of approximately 25 micrometres in size must indicate the presence of enormous amount of energy
within the grain before the shock unloading. This energy can be provided, in particular, by shock loading
preceding the shock unloading.
The paper discusses a new shear rupture mechanism which can provide the combination of extreme dynamic
compressive loading followed by shock unloading within some special zones of the fault. According to this
mechanism a general fault develops as a cascade of segments triggered in series one after another.
Interaction and linkage of the segments propagating toward each other at a relative speed comparable with
shear wave speed can cause shock-like loading-unloading impulses necessary for the particle formation due
to specific structure of linkage zones.
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Shock Loading-Unloading Mechanism in Rockburst Shear Fractures in Quartzite Causing
Genesis of Polyhedral Sub-Particles in the Fault Gouge B.G. Tarasov, W.D. Ortlepp
192 Deep Mining 07, Perth, Australia