Page 228 - Whole Earth Geophysics An Introductory Textbook For Geologists And Geophysicists

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seismic
shear-
p)
the
that
resist
the
(bulk
When
to
waves
velocities
soft
211
waves
glass
that
boundary
veloc-
the
Three
as
down
S-wave
(Jow
of
that
suggests
observation
“Moho”),
is
a
:
to
properties
7.29a).
seismic
seismic
changing
layers
through
resist
discontinuities.
Interior
region
us
from
soft
slow
able
wave
core
tells
an
through
cannot
gross
(Fig,
(refracted)
waves
Earth
velocity,
transmit
for
be
passing
Earth’s
the
thus
shear
of gradually
(or
waves. The
elastic
core/inner
must
order
Earth
the
Fluids
that
that
0)
the
slowly
boundary
of
across
and
for
of light
in
to
=
material
the
of
the
abruptly
In
Probes
observation
changes
suggests
(V,
materials
above.
determined
zero).
compressional
nature
material.
7.29b),
more
shear
of
outer.
because
core
velocity
center
rays
as
the
be
presented
crust/mantle
encountering
bent
travel
transmit
Waves
outer
gross
as
thus
(Fig.
of
the
not
example,
The
curve
the
the
much
ability
are
seismic
be
Core
waves
must
density
Earth’s
asthenosphere
the
and
Seismic
to
material.
of
can
7.28),
waves
cannot
raypaths
Law,
equations
surface
state
and
interpret
waves. The
1,
[.])
boundary,
Seismic
for
in
7.30a).
the
Upon
of
modulus,
through
(Fig.
Snell's
that
Mantle
they
changes
physical
material,
modulus
2)
approximations
the
layers,
are
(high
curves
V,
observation
waves.
(Fig.
waves.
to
from
therefore
to
of seismic
the
and
travel
core
help
shear
examples
according
Crust,
the
7.31). Within
drastic
stiff
fluid
shear
a
determined
of seismic
encounter
trave]-time
V,
of seismic
through
criteria
don’t
about
7.26).
(the
through
mantle/outer
the
is
0),
7.30b).
and
of
core
prism. The
Transmission
are
with
using
=
bent
shearing
S-waves
notable
(Fig.
observations.
us
Divisions
[k]
(yw
Three
travel
Bending
outer
there
Velocity
(Fig.
(Fig.
been
than
they
on
tells
combined
by
ing
are
modulus
ity
Based
Earth
have
3)
2)
1)
Major
FIGURE Earthquake phases. (opposite) 7.27 phases. compressional-wave Raypaths for selected a) the mantle. through refracted P-wave = P again. refracted Earth’s surface, then mantle. reflected at the through refracted P-wave = PP the surface. at twice reflected P-wave = PPP mantle. through the back outer core, then the mantle, through the fro

Seismology
Earthquake
° Mantle
Chapter7
210