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1 Acta Geophysica Polonica

1 2001

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Earthquake fracture-band theory

Teisseyre R., Teisseyre K., Górski M.

Acta Geophysica Polonica

2001

Vol. 49, nr 4

463-479

We present the theory of general structure of fracturing in an earthquake source; this new model is based on generalization of the shear band model presented in pervious papers. These models of the seismic source zone are based on the thermodynamics of line defects. In the thermodynamics of line defects the dislocation superlattice plays an essential role. The concept of line vacancy (vacant dislocation) enables us to construct a superlattice consisting of dislocations and vacant dislocations. The model introduced applies to plastic deformations; stress load increase may lead to some changes in dislocation density related to the superlattice. Such changes can also be related to a change of the number of vacant dislocations or to a change of the superlattice parameter. An increase of the number of dislocations corresponds in this case to a hardening process and is related to the spatial structure of superlattice. A pronounced plastic deformation is realized through the formation of shear bands; the dislocation number becomes multiplied along the shear planes and in consequence exceeds the number prescribed by the superlattice structure which, however, will be perservered in the direction perpendicular to the shear band planes. Our new generalization takes into account the tensile and shear fracturings forming the concurrent processes; however, some phase shifts between them shall be included. Moreover, in this paper the earthquake structure model may be not only related to the microdefect distribution, but also to an existence of macro-defects bound to a fine structure of focal region. This fine structure can be formed by some elements of the fracture space or by a certain distribution of the grains. Properties of such structures are described by the micromorphic theory. Moreover, we will not split, in a heuristic way, the deformations into the elastic and plastic parts, because the plastic phenomena are to some extent included here by the micromorphic or, as one can say, the granular/block structure properties of the medium. Applications for an analysis of earthquakes, mining tremors, volcanic events and icequakes are presented.