Study on Temporal Variations of S Wave Anisotropy in the Mantle.

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In order to study the possibility that features of the S wave polarization anisotropy in the D" layer change quickly, we analyze the splitting of ScS waves which are radiated from deep earthquakes around Japan and recorded stations in Japan. The used seismological records are those obtained by Japan Meteorological Agency and several universities. Including results reported previously by us and other researchers, we obtain 35 azimuths of the anisotropic pricipal axes for the last three decades. The temporal variation of the azimuths shows that the directions of pricipal axes do not change with time at least in an order of ten years. However, the data suggests that there is a possibility of the temporal variation of the axis direction in a longer period.