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Seismic wave simulations in the Earth's
mantle Seismologists learn about the interior of the earth by studying
the effects of Earth structure on the propagation of elastic (seismic)
waves. The linked movie shows a simulation of seismic waves propagating
in the Earth's mantle. The colors show horizontal motion in and
out of the figure or movie) recorded at distances of 30, 60, and
90 degrees (i.e., 1/12, 1/6, and 1/4 of the way around the Earth)
from an earthquake. Corresponding ground motions at the surface
as time advances (seismograms) are shown at top . The example
movies here - avi
(7.3 Mb) or shockwave
(6.29 Mb) format - are for a simulated shallow (crustal) earthquake
located at a depth of 20 km. Red colors represent motions out
of, and blue colors represent motions into, the figure or movie.
Individual wavefronts are visible in the movie from the direct
wave, as well as from the waves reflected from the liquid outer
core (the black interior of the Earth cross section). Because
of the wave propagation model used, and the direction of motion
depicted, all waves shown in the simulation are shear waves, which
propagate due to the elastic response of solid materials - a change
in shape. The large signals bound to near the surface appearing
in the latter part of the seismograms are a type of surface wave
called a Love wave. A reference earth model that
varies only with depth determines the speed at which the simulated
seismic disturbances travel. Local variations of actual observed
seismic signals compared against such simulations are used to
assist Earth scientists in infering the 3-dimensional structure
of the planet.
More of these fascinating simulations and details on how they
were calculated are available at http://epsc.wustl.edu/~saadia/page2.html.
All simulations and animations were created by Saadia Baker (http://epsc.wustl.edu/~saadia/index.html)
and Michael Wyssession (http://epsc.wustl.edu/seismology/michael/michael.html)
of the Department of Earth and Planetary Sciences, Washington
University in Saint Louis.
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