Seismologists to map the mantle



A. Dziewonski and J. Woodhouse of Harvard University have developed new seismic models of the earth's mantle, according to a recent report. The calculations are the results of attempts to obtain three-dimensional seismic structures of the mantle. The formulations are mathematical fits to seismic data, essentially with no major initial assumptions as to mantle structure. That the model has features that correlate with known crustal and mantle properties has been reassuring. The report quotes Woodhouse, “This makes other patterns discovered in this study highly believable” (Research and Development, May 1984). A first finding of the model is related to the homogeneity question of the upper and lower mantle regions. Dziewonski said, “…at this point our maps show little continuity between the upper and lower mantles.” Other findings of the new models involve the roots of continental structures, which in South America and Africa extend into the transition zone to depths of about 600 km.