Long period surface waves from WWSSN, GDSN, SRO and GEOSCOPE stations are analysed to obtain the dispersion of surface waves in the North-East of Africa. Lateral variations of Rayleigh wave velocities are retrieved simultaneously with the average azimuthal anisotropy. As a first result, the low velocity anomaly under the Red Sea is apparent at all periods. A second result is a nearly North-South direction of maximum group and phase velocities. This azimuthal anisotropy direction is in agreement with the direction of absolute plate motion in this region.

Anisotropy is also evidenced by simultaneous inversion of Love and Rayleigh wave dispersion along the path TAM-AGD. In the resulting models, isotropic and anisotropic, very low mantle SV-wave velocities extend up to the Moho. For SH waves, we find a strong discrepancy with SV waves, SH-wave velocities being higher by 5% down to 200 km under the crust. This is characteristic of lithospheric polarization anisotropy.

The S-wave anisotropy (polarization and azimuthal) found in this region, including the Red Sea, is compatible with the absolute motion of the African plate; it can be interpreted, considering the low lithospheric S-velocities, as a consequence of plastic flow in the weak lithosphere of an anomalous mantle. The anisotropy, evidenced here on S waves, may be due, as Pn and lithospheric S-wave anisotropy found in other continental areas, to dynamical processes related to plate motion. ¿ American Geophysical Union 1988