Open AccessEvidence for anisotropy in the upper mantle beneath Eurasia from the polarization of higher mode seismic surface waves
Author(s) -
Crampin Stuart,
King David W.
Publication year - 1977
Publication title -
geophysical journal of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.302
H-Index - 168
eISSN - 1365-246X
pISSN - 0016-8009
DOI - 10.1111/j.1365-246x.1977.tb03701.x
Subject(s) - anisotropy , rayleigh wave , surface wave , geophysics , geology , isotropy , love wave , seismic anisotropy , polarization (electrochemistry) , seismic wave , rayleigh scattering , wave propagation , mantle (geology) , physics , longitudinal wave , mechanical wave , optics , chemistry
Summary. Analysis of NORSAR records and a number of Soviet microfilms reveals second‐mode surface Caves propagating along paths covering a large part of Eurasia. These second modes in the 6–15‐s period band are frequently disturbed by other surface‐wave modes and by body‐wave arrivals. However, in all cases, where the modes appear to be undisturbed and show normal dispersion, the Second Rayleigh modes have a slowly varying phase difference with the Second Love modes. This coupling has the particle motion of Inclined Rayleigh waves characteristic of surface‐wave propagation in anisotropic media, where the anisotropy possesses a horizontal plane of symmetry. Numerical examination of surface wave propagating in Earth models, with an anisotropic layer in the upper mantle, demonstrate that comparatively small thicknesses of material with weak velocity anisotropy can produce large deviations in the polarizations of Inclined Rayleigh Second modes. In many structures, these inclinations are very sensitive to small changes in anisotropic orientation and to small changes in the surrounding isotropic structure. It is suggested that examination of second mode inclination anomalies of second mode surface waves may be a powerful technique for examining the detailed anisotropic structure of the upper mantle.