Parameters of the Rupture Planes of the Spitak Focal Zone Constructed by Averaged Aftershock Mechanisms

The focal mechanisms of aftershocks of the focal zone of the Spitak earthquake of December 7, 1988, have been constructed. The method of averaged mechanisms is applied using data from the international seismological center. Along the boundaries of active faults of the study area, four blocks are distinguished with pairs of compressive tension forces different in directions. The prevailing types of movements in the foci of the Spitak earthquake aftershocks are revealed. It is shown that the prevailing uplift type of movement in the aftershock foci changes from the rupture of the Spitak earthquake in the northern and southeastern direction to the predominant shear type. Solutions of the averaged mechanisms for the selected blocks, the parameters of faults, the angles of incidence and strike, and the types of movements are obtained. It is shown that the nodal planes reflect tectonically active faults.