EVIDENCE FOR UPPER-MANTLE ANISOTROPY BENEATH SOUTHERN GERMANY FROM LOVE AND RAYLEIGH-WAVE DISPERSION

We advance evidence for the existence of seismic anisotropy in the upp er mantle beneath Southern Germany from the dispersion of Love and Ray leigh. The evidence is based upon a substantial Love-Rayleigh discrepa ncy observed between periods of 40 s and 120 s. An isotropic mantle mo del clearly fails to explain the observed dispersion curves. Systemati c inversion experiments with transversely isotropic models show that a nisotropy at depths between 70 km and 200 km is sufficient to explain the observed dispersion curves. Our data require neither anisotropy at greater depths nor anisotropy in the crust though we cannot exclude i ts presence there. A search for azimuthal anisotropy of Rayleigh wave propagation indicates a weak, but possibly insignifant azimuthal aniso tropy of about 1% for periods less than 40 s with fast directions betw een 20 and 50 degrees east of north. At larger periods azimuthal aniso tropy is less than 1% and the fast directions scatter considerably as period varies.