Page 232 - Whole Earth Geophysics An Introductory Textbook For Geologists And Geophysicists

(Physical State)
to modern divisions,
considera-
Modern
state
iron
cor-
(Si0;?):
nickel).
at
recog-
215
softer
mesosphere,
km/s). showing increase at
abruptly
to
in
physical
Asthenosphere,
were
thought
Interior
high
of silica
from the outer core to the inner core.
and
top of the
and
bend
Earth
silicates
(iron

on
boundary. Refined seismic observations led
are
7.29)
Earth's
amount
waves
the
the
based
divisions
metals
(Fig.
mantle,
at
based on gross P-wave velocity (V,,. in
of
Il)
of
increase
seismic
the
zones
Probes
divisions
j.);
curves
~
heavy
especially
classical
2)
high
transition, abrupt
major
silica);
as
that
travel]-time
core,
Seismic Waves
(relatively
modern
observations
These
three
composition,
boundary. and increase

3)
(50%-70%
silica);
(Fig. 2.3).
7.31),
from
to
in V, across lithosphere /asthenosphere
solid
led
30%
mantle/core
depth, Fig.
derived
the
silicates
chemical
hard
observations
century
were
(especially
(peridotite,
Lithosphere,
Classical divisions of Earth
mesosphere/outer core
velocities
predominately
at
km
in
early 20th
boundary and decrease
(Chemical Composition)
changes
2900
raypaths
seismic
magnesium
on
Classical
and
1)
the
Based
to
2.4):
35
respond
Refined
crust,
of
in
decrease at
based on decrease
‘about
nized
tions
(Fig.
and
7.32
1)
crust/mantle
FIGURE
abrupt

| low (relatively solid 1); high (relatively solid hard somewhat Mesosphere, II) .); ! clas- the shows 7.32 Fig. 0). # (y Core, solid Jnner (=0); V) liquid Core, Outer IV) velocities. P-wave gross to according divisions modern and sical (Fig. 7.33). components three contain plates lithospheric rigid The Lith
1) rigidity
(High they have Velocity. Seismic waves slow ‘ (Moho). Rays bend
Lithosphere because mantle 0). b) Lower mantle/outer core boundary. Outer core/inner core boundary.
and = (u (1. decreases). Crust/mantle boundary
the crust rigidity
km/s through no asthenosphere a) vertical. c)
8.1 liquid, with velocity. b) the
= Vy is a the to in toward vertical.
b
Seismology Transmission. S-waves travel it of the lithosphere Abrupt bending of raypaths at discontinuities. increase the from
Earthquake through the outer core because the mantle part horizontal because of the abrupt velocity causes rays to bend causes bending away
Chapter7 Effects of rigidity (u).a) traveling from 7.31 the in decrease Velocity increase
214 7.30 0).No S-waves trave} when FIGURE toward Abrupt
FIGURE # (» down