Shear Fractures of Extreme Dynamics
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- 作者：Boris Tarasov
- 关键词：Rock fracture dynamics ; Shear rupture mechanism ; Fault strength weakening ; Fan ; hinged shear ; Velocity ; weakening and weakening ; velocity concepts ; Physical and mathematical models
- 刊名：Rock Mechanics and Rock Engineering
- 出版年：2016
- 出版时间：October 2016
- 年：2016
- 卷：49
- 期：10
- 页码：3999-4021
- 全文大小：5,463 KB
- 刊物类别：Earth and Environmental Science
- 刊物主题：Earth sciences
Geophysics and Geodesy
Civil Engineering - 出版者：Springer Wien
- ISSN：1434-453X
- 卷排序：49
文摘
Natural and laboratory observations show that shear ruptures (faults) can propagate with extreme dynamics (up to intersonic rupture velocities) through intact materials and along pre-existing faults with frictional and coherent (bonded) interfaces. The rupture propagation is accompanied by significant fault strength weakening in the rupture head. Although essential for understanding earthquakes, rock mechanics, tribology and fractures, the question of what physical processes determine how that weakening occurs is still unresolved. The general approach today to explain the fault weakening is based upon the strong velocity-weakening friction law according to which the fault strength drops rapidly with slip velocity. Different mechanisms of strength weakening caused by slip velocity have been proposed including thermal effect, high-frequency compressional waves, expansion of pore fluid, macroscopic melting and gel formation. This paper proposes that shear ruptures of extreme dynamics propagating in intact materials and in pre-existing frictional and coherent interfaces are governed by the same recently identified mechanism which is associated with an intensive microcracking process in the rupture tip observed for all types of extreme ruptures. The microcracking process creates, in certain conditions, a special fan-like microstructure shear resistance of which is extremely low (up to an order of magnitude less than the frictional strength). The fan-structure representing the rupture head provides strong interface weakening and causes high slip and rupture velocities. In contrast with the velocity-weakening dependency, this mechanism provides the opposite weakening-velocity effect. The fan-mechanism differs remarkably from all reported earlier mechanisms, and it can provide such important features observed in extreme ruptures as: extreme slip and rupture velocities, high slip velocity without heating, off-fault tensile cracking, transition from crack-like to pulse-like rupture mode at variation in loading conditions, dramatic embrittlement of hard rocks at highly confined compression, abnormally low transient strength of hard rocks at high confining stresses, etc. All these questions are discussed in the paper.