Lateral variations of the structure of the crust-mantle boundary from conversions of teleseismic P waves
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Vols. 1-18 (1924-1944), ISSN 0044-2801
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Abstract
Clear P-to-S converted phases are observed in teleseismic seismograms recorded at the Grafenberg array. The seismic events used are nuclear explosions from east Kasakh and deep-focus earthquakes from the region of Japan and central Asia. The identification of the converted phases has been improved by the rotation of the coordinate system. Theoretical seismograms have been computed to obtain the response of various velocity structures of the lithosphere under the receivers, using the reflectivity method of Kind (1985) for different source and receiver structures. The interpretation of the P-to-S conversions leads to a model of the crust-mantle transition zone with a first-order discontinuity and a normal velocity contrast in the north, an increased velocity contrast in the centre, and a reduced sharpness of the discontinuity in the south of the array. The sedimentary layers underneath the stations also cause strong converted phases, and they also influence strongly the waveform of the incoming P wave.
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References
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