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View of 3-D grid used to illustrate seismic
wave propagation. The mesh (grid)
represents a volume of elastic material through which waves can propagate in
the direction shown. The 3-D grid is
shown in perspective view to demonstrate the wave propagation effects and
particle motions of the different wave types in all directions. In the animations shown below,
Compressional, Shear, Rayleigh and Love wave propagation through the elastic
material is illustrated. In this 3-D
volume, the grid is designed to have an upper surface (corresponding to the
Earth’s surface) that consists of a boundary with a vacuum or very low
density fluid above so that surface wave propagation (Rayleigh and Love
waves) as well as body wave propagation (Compressional and Shear waves) can
be illustrated. All
wave types are designed to propagate in the X direction and parallel to the
Earth’s surface. The wave animations
illustrate wave characteristics and particle motion as listed in Table 1. However, no decrease in energy or amplitude
with distance due to spreading out of the wave energy (geometrical spreading)
or loss of amplitude caused by absorption of energy (sometimes called
attenuation) by the media (due to anelasticity) are included. The elastic material is also assumed to be
isotropic (velocity and other physical properties are the same for all
directions of propagation), therefore, no anisotropy is included in the
animations. Furthermore, for the
surface wave animations, no dispersion (variation in wave velocity with
frequency) has been included. The
seismic wave animations were created using a Matlab code and then converted
to an animated GIF format. |
