Authors: Leif Karlstrom: Department of Geophysics, Stanford University, Stanford, California;
Shaul Hurwitz, Fred Murphy and Malcolm J. S. Johnston: U.S. Geological Survey, Menlo Park, California;
Robert Sohn: Woods Hole Oceanographic Institute, Woods Hole, Massachusetts;
Jean Vandemeulebrouck: ISTerre, Universite de Savoie, CNRS, Le Bourget-du-Lac, France;
Maxwell L. Rudolph: Department of Physics, University of Colorado, Boulder, Colorado;
Michael Manga: Department of Earth and Planetary Science, McCone Hall University of California at Berkeley, Berkeley, California;
R. Blaine McCleskey: U.S. Geological Survey, Boulder, Colorado.
5. Seismic studies provide new detail on transition zone below western US
At certain depths in Earth's mantle, the increasing pressure causes minerals to undergo phase changes, transforming to different crystal structures. Seismic waves change speed at these discontinuities, so analyzing seismic waves gives scientists information about the structure of the mantle.
To gain more detail about the fine structure of the transition zone beneath the western United Statesthe zone between the upper and lower mantles, bounded by discontinuities at 410 kilometers (255 miles) depth and 660 kilometers (410 miles) depthTauzin et al. analyzed seismic waves recorded at seismic stations of the U.S. transportable array. For instance, they imaged the area where the Gorda plate, which subducted under northern California, flattens and causes uplift of the 410 kilometer (255 mile) discontinuity under northern Nevada.
They also find that the transition zone is thicker below Washington, Oregon, and Idaho. In addition, they identify minor negative discontinuities (where seismic wave velocity decreases with depth rather than increases) at around 350, 590, and 630 kilometer (217, 367 and 391 mile) depths, and show that the 350 kilometer
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American Geophysical Union