Science Opportunities - Basic Research Opportunities in Earth Science - page 66

FIGURE 2.14 Seismic tomographic image of the shear velocity of the Earth's
mantle (G. Masters, G. Laske, H. Bolton, and A. Dziewonski, The relative
behavior of shear velocity, bulk sound speed, and compressional velocity in the
mantle: Implications for chemical and thermal structure, in S. Karato, et al.,
eds., Earth's Deep Interior: Mineral Physics and Tomography from the Atomic
to the Global Scale, Geophysical Monograph 117, American Geophysical
Union, Washington, D.C., p. 63-87, 2000). Shown are perturbations with respect
to the spherical average, where blue and red mark isovelocity surfaces for +0.6
and ` 1.0%. Top: The map view of the shallow structure reveals seismically fast
areas beneath continents and the old Pacific Ocean, whereas slow areas are
found along midocean ridges. Bottom: View of the whole mantle from south to
north (Africa to the left). Large-scale, low-velocity regions (sometimes described
as megaplumes) are surrounded by fast, relatively narrow, slablike regions that
extend across the whole mantle. The “ring” of fast velocities around the mid-
Pacific low-velocity anomaly at the bottom of the mantle is thought to be the
“graveyard of subducting slabs.” SOURCE: Reprinted with permission from P.
Tackley, Mantle convection and plate tectonics: Toward an integrated physical
and chemical theory, Science, v. 288, p. 2002-2007, 2000. Copyright 2000
American Association for the Advancement of Science. +0.6% (blue) and
`1.0% (red)