Visualization of Rayleigh Wave Propagation in the Mountain Root Structure

The wavefields of Rayleigh-wave propagation in the mountain root structure (MRS) of the western Tien Shan are computed and visualized using the finite-difference method. The incident Rayleigh waves have a predominant period of about 23 s, which corresponds to a wavelength of 90 km. Vertical-component wavefields at selected times are shown as the waves pass the MRS. These wavefields indicate that passage through the MRS continuously generates scattered waves that form semicircular wavefronts with centers distributed along the MRS. From the wavefield analysis, the wavelengths of the reflected Rayleigh wave scattering are estimated to be 90―100 km. Using a theory for resonant standing P and S waves generated in the MRS by incident Rayleigh waves, we estimate a wavelength of 90 km and a dominant period of 23.1 s for the scattered S waves based on the elastic parameters of the MRS. These properties of the scattered S waves are close to those of the incident Rayleigh waves. For comparison, wavefields for a stratified medium and for an MRS model including low-velocity zones are also shown.