Earthquake fragmentation and slip processes: Spin and shear-twist wave mosaic

We follow our former considerations on rotational processes and emission of rotation and shear-twist waves as occurring in earthquake source zones. A concise presentation of the motion and constitutive relations is given for each type of the four fundamental point deformations: displacements, rotations, point stretch/squeeze, and string-string point deformations (shear nuclei).     

Fluid theory with asymmetric molecular stresses: Difference between vorticity and spin equations

We present a new development in fluid theory, incorporating into it the velocity and spin fields; special attention is given to the structure of transport.The theory includes asymmetric molecular stresses and independent rotation velocity, i.e., spin. Our approach is based on our former studies on the asymmetric continuum theory with the balance and constitutive laws for displacement velocity and independent rotation motion, and points out the role of a related characteristic length unit. It is assumed that the vorticity caused by velocities can induce a spin transport counterpart. Thus, under certain conditions, an additional transport term due to rotational velocity fields may be incorporated to the velocity transport, which may lead to the vortex fields included directly into the theory.     

Possible mechanism of rockbursts in coal mines

One of the important questions of rockburst prevention is the understanding of the mechanism of rockburst source. This question can be effectively studied by direct seismic observations in the rockburst regions. For this purpose, the distribution ofP-wave onset signs and the inversion of first motion amplitudes were utilized as the basic method. In such a way the coal mine regions in Poland (Upper Silesia) and in Czechoslovakia (Kladno coal mine district) were studied as part of the Polish-Czechoslovak rockburst investigation project. More than 250 rockburst events were recorded here in the decade 1977–1983, and analyzed. The results of the statistical analysis of these data allow us to formulate and introduce a model of the rockburst source with an implosion component. The suitability of this conception was verified by laboratory simulation conditions; it was confirmed that the seismoactive displacements with a clear implosive component were recorded in the neighbourhood of a stress concentrator weakened by holes. The results of both the field observations and laboratory tests were in good agreement with the theoretically derived radiation patterns for a combined shear-implosive source and also with the theoretical conception of such a source based on real geometrical configurations of mine excavations and tectonic dislocations.The rockbursts treated exhibit a dominant shear component, the magnitude of the additional implosive component not exceeding 10 percent of the shear component.     

A method to minimize errors in seismic differential measurements

The seismic differential signal is measured as a difference between two seismic recordings made by seismometers placed in the same direction close to each other. The purpose of our study was to verify possible inherent errors in the measurement technique, especially in far-field measurements.     

Asymmetric continuum and anisotropy

We present a relation between stress moments and antisymmetric part of stresses and the related constitutive law joining those stresses with the particle/point rotations. Correspondence of the asymmetric continuum theory to the micromorphic theory is considered. An extension of the asymmetric continuum theory for the case of 2D anisotropy for antisymmetric stresses leads us to the problems of friction anisotropy and fracture pattern.     

Magneto-telluric recordings from the Friuli seismic zone, northeast Italy

Magneto-telluric measurements were undertaken in the Friuli seismic area of north-east Italy. The purpose was to find possible correlations between magneto-telluric signals and seismic activity. Two stations were operational between July 1987 and June 1988. Apparent resistivity curves were found for September 1987 and January 1988 data, and a magneto-telluric inversion problem was solved. Artificial noise and natural disturbances of the electromagnetic field, especially those related to tectonic processes, are discussed.     

Earthquake processes in a micromorphic continuum

Summary The paper introduces a new model earthquake process based on the theory of micromorphic continua. The processes in a focal region are described by deformations of microstructure in time. It is assumed that the fracturing processes as well as phase transformation of metamorphic phenomena have caused in the past certain non-reversible changes which determine the microstructure of focal region. These internal microstructural elements form the attaching points around which the couple stresses arise. The properties of focal region are determined by the constitutive equations. The micromorphic mechanics considers the existence of body couples as determined by a regional stresses and looks after a response field of stresses, stress moments and strains in the focal region. Further, it is explained how microdislocation field is connected with microdeformations and micromorphic structure. In the considered earthquake structure model a microanisotropy is assumed through the tensor of microinertia. This tensor describes a distribution of microelements. Simple solutions of wave processes in a focal region are presented. The dispersion of waves is discussed.     

Induced strains and defect continuum theory: Internal reorganization of load

Induced strains play an important role in mining regions and water dam areas. We consider a mechanism of reorganization of the applied stress load by some changes in rock-body defect distribution caused by human activity. A defect content increases with increasing stress load and related deformations; hence, a relationship could appear between seismic risk and deformation level. Recent progress in the Asymmetric Continuum Theory permits to consider some internal reorganization of the applied load due to internal defect content and distribution; in this paper we consider an increase of internal defect densities due to mining works and the appearance of reorganized internal stress distribution.     

Release-Rebound Processes: Vector Motions

The tensor relations describing the shear deviatoric strains and rotation strains may be presented as vector relations in a special coordinate system, e.g., in the diagonal or off-diagonal one. However, these fields can be also presented in the 4D invariant forms by means of invariant Dirac tensors. We present 4D relativistic relations for the invariant shear deviatoric strain and rotation strain vectors closely related to a fracture process in solids and to the molecular strains (shear and rotational) in fluids. These shear and rotation strains may interact with the radial derivatives of pressure along the propagation directions.