Abstract

The lowermost (D’’) mantle as well as the core-mantle transition zone are rather complex areas in terms of seismic wave propagation. We search for low-amplitude reflections from the lowermost mantle in recordings from two seismic arrays in Germany, the permanent Gräfenberg Array and the semi-permanent Eifel Array, constructed from stations of the Eifel seismic network. As sources about 120 earthquakes are analyzed at distances from 70°-80° all around the world to find anomalous P-phases such as PdP originating from the lowermost mantle. By applying array techniques, such as beamforming and frequency-wavenumber analysis, each earthquake has been individually checked whether the waveforms contains an anomalous phase (PdP) or not between the direct phase (P) and the core reflection (PcP). For identified PdP phases the reflection points above the core-mantle boundary are plotted together with known seismic anomalies to produce maps with structural anomalies. A clear pattern of reflectors is found undernearth northern Siberia, the Kara Sea and the eastern Arctic Ocean which may be the remnants of an old subducted plate.