MANTLE DISCONTINUITIES BENEATH THE STATIONS MDJ AND HIA AND ITS IMPLICATIONS

Abstract

Digital broadband seismograms recorded from 1988 to 2000 at the stations of MDJ and HIA were used to study the mantle discontinuities and the influence of subducting slab under the Japan Sea on the 660km discontinuity beneath the two stations by using P-SV converted phases. In order to increase the reliability of results, the rectilinearitypolarization filter analysis and modified N-th root slant stack methods were used to pick out P-SV converted phases. Appropriate smoothing and constraint of cubical angle were applied to the filtering; the modification of focal depths and correction for the inclination of discontinuities were used in the stacking. It was found that there are mantle discontinuities at the depths of 660, 410, 220 and 520km under the stations of MDJ and HIA. Besides that, the radial structures of the mantle are complicated and there are still some relatively strong discontinuities near the depths of 140, 350, 570, 740 and 1080km. It is shown that the structure between 660km and 840km under MDJ station is more complicated than that under HIA station. It may show the influence of subducting slab on the 660km discontinuity beneath MDJ station.