Mapping Earth Structure

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9316441 Helmberger This research is to determine the detailed nature of the lateral variation in the D" layer of the earth's mantle, the portion just above the earth's core. Most of the present methods that image this deep structure must correct for the intervening mantle structure. Since there is poor consistency in derived mantle structure, most 3-D global models predict discordant differential times for core-phases, branches of PKP and SKS. This work will use differential times and waveform information to assess lateral variation in the deep mantle structure from the bottom-up, as opposed to the normal procedure of top-down. However, this requires a great deal of study of the inner and outer core to establish their uniformity so that variation in differential times are mapped properly. ***