In this thesis an attempt is made to demonstrate in accordance with known physical principles that significant changes in the macroscopic equilibrium of the earth can be attributed to rate processes which do not call upon the existence of macroscopic gradients and disturbances in the earth.Such processes and their relation to known mechanisms of plastic deformation and to the experimentally established behavior of materials under high pressures are criticallyevaluated. This evaluation is carried out in the light of some well-established concepts of statistical mechanics and modern physics. In so doing specific methods for producing seismic disturbances which are based upon known mechanisms of plastic deformation and rupture become indicated. It is also shown that under very high pressures, pressure and temperature can complement each other in producing disturbances associated with polymorphic transitions of materials leading to a reduction insymmetry of their lattice structure.
A specific mechanism for producing and repeating earthquakes at shallow and intermediate depths is proposed. This mechanism is based upon the existence of a visco-elastic surface layer supported by a plastic material embodied with stress relaxing properties.
The effect of such a configuration upon the propagationof Love Waves is investigated quantitatively. This investigation shows that the plastic sub-layer would explain the observed selection of the period of Love Waves.
