Based on the theory of surface waves in a media with weak lateral heterogeneities, an explanation
is given for the peculiarities that are considered as prospecting indicators in the microseismic sounding
method (MSM). According to this theory, during the propagation of surface waves in such media, their local
characteristics are the same as in the case of propagation in a horizontally homogeneous medium characterized
by the same vertical velocity section as underlying a given point. Since the wave energy flux through a
semiinfinite vertical strip is conserved, the amplitude of the wave is redistributed along the vertical. Based on
this principle and simple physical considerations, it is shown that above a low-velocity domain, the amplitudes
of microseisms should increase at wavelengths approximately exceeding the depth of the anomaly by a
factor of three and decrease at small wavelengths. The model calculations show that variation of spectral
amplitudes only allows a depth to the anomaly to be estimated rather than its average extent. Practically identical
spectra characterize the anomalies in which the product of the vertical extent of the anomaly and the
velocity contrast is approximately similar.