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Spin and twist motions in the earthquake preparation processes: Analysis of records

Teisseyre K.

Acta Geophysica

2011

Vol. 59, no. 1

5-28

Three seismic events in L’Aquila region and one in western Greece have been chosen for comparative analysis of two kinds of seismic motions, spin and twist. These torque components of the seismic field were detected in horizontal plane with the rotational seismometers. Homologous parts were sought in the signals of spin and twist components – curve of one component was compared to the other directly and after transformations: phase-shifting and sign reversal. To achieve better clarity, these operations were done on the data divided into several descendant signals with the use of band-pass filtration. Conformities of spin and twist, revealed in this way, are assumed to be results of distant processes in the source, where relations between rotational and shear motions include retardations. The analysis embraced also the time-period preceding an earthquake, and the conformities found here are attributed to phenomena occurring in the focus just before the rupture.

Spin and twist motions in a homogeneous elastic continuum and cross-band geometry of fracturing

Teisseyre R.

Acta Geophysica Polonica

2004

Vol. 52, nr 2

173-183

A uniform continuum with rotation motions of spin and twist type is presented; in this approach we supplement the ideal elasticity constitutive law, the strain-stress relation, by the rotation-asymmetric stress relation. In such a way, we can evade an influence of the Hook law, which, when used as the unique law in the ideal elasticity, rules out an existence of rotation waves. Thus, in the ideal elastic continuum the rotation vibrations can propagate and are not attenuated. The asymmetric elastic rotation fields and their relation to asymmetric elastic stresses are proposed and discussed, under the condition that the total fields with the elastic and self parts remain symmetric or antisymmetric as required by the compatibility conditions. The tensor of incompatibility splits into the symmetric or antisymmetric parts. The conservation and balance laws for spin and twist fields and the stress -related equations of motion for symmetric and antisymmetric parts of stresses are given. The relations obtained for elastic fields, expressed by difference of the total and self-fields, can be split into the self-parts prevailing on the fracture plane and the total parts describing seismic radiation field in a surrounding space. The role of rotation processes in premonitory and rebound time domains is considered in estimating the most effective fracture patterns.