Abstract
Concepts of materials science are applied in an attempt to describe the growth and properties of shear or fault zones which are associated with deep focus earthquakes. Aspects of fracture toughness, dynamic recrystallisation and superplasticity are used to model the observed characteristics of such zones. The fault or shear zone is considered to be composed of very fine grained rock which is capable of deformation by the mechanism of “superplasticity” such that it has little resistance to shear as compared with the surrounding rock mass. This “superplastic crack” will therefore have an associated region of concentrated shear stress around its perimeter which, at typical rock temperatures of greater than half the melting point, will continuously promote dynamic recrystallisation. In this way the fault is self-propagating until growth velocities are reached which do not allow sufficient time for the recrystallisation process to occur. The intermittent activity of earthquakes is thus in qualitative agreement with the theory.
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