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

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.