Abstract. Phase delays of Rayleigh and Love waves from teleseismic earthquakes recorded during the Southern Africa Seismic Experiment have been inverted for upper-mantle seismic velocities along the propagation paths and beneath the station array. Successful models of subarray structure displayed significant radial anisotropy in the uppermost mantle but no shear-wave low-velocity zone, supporting the hypothesis that the lithosphere beneath the Kaapvaal craton is thick. The azimuthal variations of Rayleigh-wave slowness are not consistent with simple models based on $KS splitting observations and anisotropy measurements of Kaapvaal mantle xenoliths. This discrepancy may imply some amount of small-scale heterogeneity in anisotropy.

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Abstract. We present the first waveform migration for the lower mantle, focusing on the lowermost 400 km of the mantle beneath northern Siberia. We migrate vertical component ? wave seismograms recorded in western Europe for earthquakes located in the Kuril Islands region. We focus on the time window between the direct P wave and the ?c? wave, reflected at the core-mantle boundary, and we investigate the origin of precursors. The data, selected for their good signal-to-noise ratio, are deconvolved by the source time function determined by the beam of the P wave. We observe the signature of a finite size scattering object located around 75øN, 85øE, at an apparent depth of •2650 km with respect to the IASP91 model. Its scale length is probably of the order of 100 km. This object is characterized by an anisotropic scattering diagram and may be related to the presence of an ancient subducted plate near the core-mantle boundary.

length smaller than 1ø). The first onset times observed at distances larger than 85 ø are compatible with a D" velocity about 1% larger than standard models along these paths, up to a depth of 2850 km. By one dimensional forward modeling we find one model with a 2.8% discontinuity at 2605 km depth, another with a 7 km thick 3% low velocity lamella at 2607 km depth. They both generate waveforms which fit the data similarly.