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geo 15 - discontinuity is confirmed in this region and the...

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Investigating topography of upper mantle discontinuities in the Southwest Pacific using a migration method. Tine Thomas, University of Liverpool Magali I. Billen , University of California, Davis. Due to the temperature dependence of the phase transitions of upper mantle minerals the upper mantle discontinuities hold insight into Earth dynamics and can give information on temperatures of slabs. In regions of cold downwelling (i.e. slabs) the discontinuity at 410 km depth is raised whereas the 660 km discontinuity is lowered. But the discontinuity at 520 km depth has yet to be analysed in more detail. We employ a migration method and underside reflections of PP off these discontinuities to investigate their topography in the upper mantle beneath the Southwest Pacific. With this method the existence of the 520 km
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Unformatted text preview: discontinuity is confirmed in this region and the deflections of 660 and 410 km are studied. The underside reflection P660P that was recently considered to be absent is visible with the migration method in these regions. The results show that the 660 km discontinuity seems to be lowered up to 40 km whereas the 410km discontinuity seems to be only slightly raised near subduction areas and the data show laterally varying topography on all observed discontinuities. Using the depths of the discontinuities we are attempting to constrain the temperature within and in vicinity of the slabs. The 520 km discontinuity is detected in the whole dataset and seems to be much lower in our studied region. In addition discontinuities at 220 and 350 km are observed....
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