Problems of the tectonophysical characteristics of stresses, deformations, fractures and deformation mechanisms of the earth's crust

Abstract

The present paper represents a more profound variant of the report delivered at the 15th General Assembly of the I.U.G.G., Moscow, August, 1971. The paper deals with a number of principal questions of tectonophysics, it contains methods and the results of objective quantitative estimations of physical values (deformations, stresses, etc.), which characterize the tectonic processes. The basic points are given of the new method of defining the value of plastic deformation γ III of natural structures according to their morphology; first examples of such an estimation for typical folding structures give values of γ III ranging from 0.2 to 0.6. A preliminary scheme of the changes in the viscosity of the earth's crust with depth is given, while the correlation data between viscosity and absorption of solids and the dependence of the viscosity on stresses are also taken into consideration. It is shown that the viscosity of the plastic flow within the crust increases with depth. Methods of the study of natural tectonic stress-fields and the stress-fields of models are discussed. Correlation of some quantitative data concerning recent and ancient slow movements of the crust of the earth, deformations, fractures, crackings, earthquakes (on the territory of the U.S.S.R.) leads to the determination of various trends and the limits of the principal stress values in different regions. Areas with different values of maximal shear stress τ max were singled out on the territory of the Soviet Union. The most widespread mechanisms deforming the earth's crust are singled out for attention. The results of field observations, of the study of plastic and elastic models and of theoretical solutions with calculations made on a computer, make it possible to characterize the distribution of deformations, fractures and stress-fields, which are typical of these mechanisms. Theoretical investigations, connected with the problems of tectonophysics, are conducted in two main directions: 1. (1) the creation and development of the general theory of large plastic deformations of shells from homogeneous or nonhomogeneous material (nonhomogeneity is due to the influence of active outer-fields); 2. (2) description by the method of mechanics of some of the concrete tectonic processes and with the determination of stresses and of the velocity of displacements (problems of the formation of overthrusts, displacements of the earth's surface above a downwards moving base, deformations of the crust under the influence of convectional subcrustal currents, etc.). According to modelling data obtained by polarization-optical methods, the principal regularities in the changes in a homogeneous stress-field, which are provoked by the rise of a fracture in this field, arc outlined. A complicated distribution of areas of stress reduction and increase around the fracture is determined; this distribution influences the energy of an earthquake. The results of the modelling show that some ancient tectonic faults give rise to disturbances of the recent field of stresses, the type of which is determined by the form and orientation of ancient faults. In future such disturbances may result in a strong earthquake in certain sections outside the zone of existing tectonic faults. The problem is also discussed of the value of the energy of tectonic processes which can be calculated on the base of tectonophysical data.