by LIVIU CONSTANTINESCU
Physical considerations suggest that the theoretical source of the double
couple without moment (the so-called source II) may be a better model for real
earthquake foci than the single couple with moment (source I). A weighty argument
in this respect is represented by the physical substratum of source II: dislocations.
Initially a theoretical subject of mathematical research within the framework
of the infinitesimal elasticity theory, dislocations have subsequently become
the object of studies having a more physical character. Aiming at explaining
imperfections in crystals and at applying the results also to the study of
strength in solids, particularly to special problems of metallurgy, the knowledge
arrived at in this way constitutes today an important chapter of solid-state
physics.
By adapting more or less thoroughly the concepts and results of the physical
theory of dislocations to some of the special conditions of earthquake occurrence
(macrophenomenology, finite strain etc.), earthquake mechanism studies or researches
limited to the phenomenon of fracture considered within the geophysical context
have led to a geophysical theory of dislocations with important seismological
applications and seismotectonic implications.
Beside barely geometrical "fault-plane solutions", the research methods
thus worked out are apt to provide such valuable information as that concerning
the stress-pattern at earthquake foci, size of the foci, energy release etc.
Promising prospects of development are offered by a more realistic approach
of the problem by taking into consideration the dynamic character of the phenomena
and the nonhomogeneity of the medium within which they take place.