Dynamics of geophysical medium from power spectral density of microseisms before and after earthquakes: case study of Bureya massif, Amur region

The time–frequency parameters of weak earthquakes and microseisms are studied. The qualitative and quantitative relationships of the power spectral density of seismic waves are established; these relationships vary in terms of frequency spectrum for the areas of the northeastern framing of the Tan Lu fault system and Bureya massif. The reason for these differences could be the influence of the crustal geological structure near the observations points. Resulting from the time–frequency analysis of weak earthquakes, two sites located in the Tan Lu fault zone show an increase in the power spectrum at frequencies of 1 to 5 Hz and the resonant excitation of the medium at high frequencies (12.5–35 Hz) for the area of the Bureya hydroelectric power station during the travelling of seismic waves from weak earthquakes. A longer attenuation of the power spectral density of seismic waves at high frequencies is noted, and this may occur due to resonant excitation of the medium and the influence of the dam on the geological medium. On the contrary, this effect was not observed at the second site located near Lake Udyl. It is shown that the increase in power can be attributed to the interaction between seismic waves and spatial inhomogeneities in the Earth’s crust.