Tidal Response of the Geophysical Medium as an Indicator of the Level of Seismic Stress in the Earth’s Crust

Abstract

According to records of a 75-m laser interferometer over a 15-year observation period, the deformation component of the lunar–solar tide is distinguished as a result of the reaction of the Earth’s crust to this tide. The tidal response depends on the mechanical properties of the geophysical medium, or, in other words, it is determined by the elastic coefficients at the observation point. If the medium experiences variable tectonic or other mechanical loads, then at extreme values, within the framework of the considered concept, the elastic parameters of the medium should depend on the magnitude of this load or degree of the stress state and thus change the crustal response to the tide. The article demonstrates that, for a quantitative analysis of the stress level, it is necessary to select only the main lunar wave M₂ from the total tide. The main advantage of this wave, as the article shows, is that it is less affected by variations in meteorological factors. Moreover, a complex parameter is required, namely, the amplitude factor and phase value of the observed tidal wave M₂ with respect to the theoretical value of these parameters of this wave. Only the complete set of these parameters makes it possible to correctly assess the level of stress in the geophysical medium and, as a consequence, the ability to predict the formation of an active seismic source in a local zone.