Word: dziewonski
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According to Professor of Geology Adam M. Dziewonski, hotspots underneath mid-oceanic ridges in the earth's mantle can reach depths of 300 or even 600 kilometers. This suggests that mid-oceanic ridges are active suppliers of crust-forming material, rather than simply passive openings from which hot mass flows...
...Dziewonski and graduate student Wei-jia Su are challenging a claim made last January by two California researchers that such hotspots extend to depths of only 100 kilometers. Evidence for the Harvard geologists' theory, published in today's issue of the British science journal Nature, is drawn from a new three-dimensional model of the entire mantle...
...Dziewonski and Su created the model using a technique known as seismic tomography, based on many of the same principles as CAT scans...
...Dziewonski speculated that some parameter may have been over- looked in Zhang's measurements, since somevelocities were slowed by up to 10 seconds in thenew model, but only two seconds in Zhang...
Before dealing with the core, though, scientists had to understand the intervening mantle, through which all seismic information has to pass on its way to the surface. Explains Dziewonski: "If it's a faulty lens, you're going to have a wrong image." By 1984 the Harvard group had assembled the first detailed map of the mantle ever published. Their data consisted of the patterns of earthquake-generated pressure waves that passed through the solid earth, moving faster through cooler regions of the mantle and more slowly through warmer areas...