Download Document

04- Das Erdinnere II
Thursday, 12 November 2009
Module BP 11 - 04
Examples of seismic waves
P
PKiKP
PcP
PP
PKP
PKIKP
inner
core
FOCUS
outer
core
mantle
ScS
SKIKS
SS
R. Bousquet 2009-2010
S
SKS
P-wave
S-wave
Seismic wave paths of some important refracted and reflected Pwave and S-wave phases from an earthquake with focus at the
Earth’s surface.
Thursday, 12 November 2009
Module BP 11 - 04
30
SKIKS
SKS
PKP
Travel-time, t (min)
20
PKIKP
PKIKP
PKiKP
dP
e
t
ac
ScS
fr
dif
S
10
PcP
P
core
shadow-zone
for direct
P-waves
R. Bousquet 2009-2010
core shadow-zone for
direct S-waves
0
0
Thursday, 12 November 2009
30
60
90
120
Epicentral distance, 6 ($)
150
180
Travel-time versus epicentral distance (t–∆)
curves for some important seismic phases
(modified from Jeffreys and Bullen, 1940)
Module BP 11 - 04
Fault plane solution
D
C
Ground surface
Compression
Secondary plane
Dilatation
H
Dilatation
R. Bousquet 2009-2010
Fault plane
Thursday, 12 November 2009
Compression
Module BP 11 - 04
Fault plane solution
Sensor C
1st peak upwards
Dilatation
Fault plane
Compression
Compression
Epicenter
Dilatation
R. Bousquet 2009-2010
Secondary plane
Thursday, 12 November 2009
Sensor D
1st peak downwards
Module BP 11 - 04
Fault plane solution
N
(a) focal sphere
H
P1
ltfau ne
pla
S1
S2
P2
P2
P1
R. Bousquet 2009-2010
(b) first motions
P
T
(c) focal mechanism
Method of determining the focal mechanism of an earthquake. (a) The focal
sphere surrounding the earthquake focus, with two rays S1 and S2 that cut the
sphere at P1 and P2, respectively. (b) The points P1 and P2 are plotted on a lowerhemisphere stereogram as first-motion pushes (solid points) or tugs (open points).
(c) The best-fitting great circles define regions of compression (shaded) and tension
(unshaded). The P- and T-axes are located on the bisectors of the angles between
the fault-plane and auxiliary plane.
Thursday, 12 November 2009
Module BP 11 - 04
Fault plane solution
(a) normal fault
The different types of fault plane
solution
m 3'
m 1'
P
T
(b) reverse fault
m 1'
m 3'
T
P
(c) strike–slip fault
R. Bousquet 2009-2010
m 1'
Thursday, 12 November 2009
T
P
m 3'
Module BP 11 - 04
Example of Fault plane solution: Atlantic ridge
60$W
75$N
40$W
20$W
0$
75$N
May 31
1971
60$N
September 20
1969
April 3
1972
60$N
Fault-plane solutions for
earthquakes along the MidAtlantic Ridge, showing the
prevalence of extensional
tectonics with normal
faulting in the axial zone of
the spreading center (based
on data from Huang et al.,
1986).
April 22
1979
40$N
40$N
November 16
1965
June 6
1972
June 28
1977 (1)
R. Bousquet 2009-2010
20$N
January 29
1982
June 3
1962
May 12
1983
June 2
1965
June 28
1979
January 28 1979
0$
Thursday, 12 November 2009
60$W
20$N
June 28
1977 (2)
40$W
20$W
0$
0$
Romanche fault
Module BP 11 - 04
Example of Fault plane solution: Romanche fault
n of
motio plate
n
Africa
ST. PAUL
HE
AN C
ROM
N
CHA I
R. Bousquet 2009-2010
motion of
American plate
Fault-plane solutions for earthquakes on the St. Paul, Romanche and
Chain transform faults in the Central Atlantic ocean (after Engeln et al.,
1986). Most focal mechanisms show right lateral (dextral) motions on
these faults, corresponding to the relative motion between the African
and American plates.
Thursday, 12 November 2009
ridge
dextral
transform fault
shallow
reverse fault
no
relative
motion
oceanic
plate
inactive fracture zone,
negligible seismicity
R. Bousquet 2009-2010
oblique
normal fault
sinistral
transform fault
continental plate
normal
fault
subduction zone
Module BP 11 - 04
Example of Fault plane solution
steep
reverse fault
Fault-plane solutions for hypothetical earthquakes at an ocean ridge
and transform fault system. Note that the sense of movement on the
fault is not given by the apparent offset of the ridge. The focal
mechanisms of earthquakes on the transform fault reflect the relative
motion between the plates. Note that in this and similar figures the
sector with compressional first motions is shaded.
Thursday, 12 November 2009
Module BP 11 - 04
Examples of seismic waves
P
PKiKP
PcP
PP
PKP
PKIKP
inner
core
FOCUS
outer
core
mantle
ScS
SKIKS
SS
R. Bousquet 2009-2010
S
SKS
P-wave
S-wave
Seismic wave paths of some important refracted and reflected Pwave and S-wave phases from an earthquake with focus at the
Earth’s surface.
Thursday, 12 November 2009
Module BP 11 - 04
Simple model of the earth
Surface outcrop
Seismic reflection
& refraction
Crust
Drillholes
(up to ~20 km)
Mantle
Core
R. Bousquet 2009-2010
Gravity,
magnetics,
heat flow
dimishing resolution
Earthquakes Seismic Waves
(penetrate entire Earth)
Thursday, 12 November 2009
center of Earth
(6375 km)
Magma
(fro up to ~200 km)
Module BP 11 - 04
Seismic velocities model for the Earth
Body-wave velocity (km s –1)
0
10
15
crust
35
660
1000
Depth (km)
3000
4000
R. Bousquet 2009-2010
5
410
2000
Thursday, 12 November 2009
0
5000
6000
VS
`
upper
mantle
VP
_
lower
mantle
2889
outer
core
5154
inner
core
Module BP 11 - 04
Relation Seismic waves - density
Birch’s law (1964)
0.6 GPa
Vp
Vp
1.0 GPa
Vp
Vs
Vs
Velocity (km.s-1)
Velocity (km.s-1)
0.2 GPa
extended Birch’s law
Vs
R. Bousquet 2009-2010
Density (g.cm-3)
V=aρ+b
where a & b are parameters
characterizing the rocks and V & ρ are
respectively the seismic velocity and the
density of the rocks
Thursday, 12 November 2009
Density (g.cm-3)
Ludwig et al., 1970
Module BP 11 - 04
Simple model of the earth
Density differentiation
due to changes
in chemical composition
Crust
2-3 t/m3
3-3 t/m3
Silicates
Mantle
5.8 t/m3
Core
Iron
R. Bousquet 2009-2010
10.8 t/m3
Thursday, 12 November 2009
Silicates
rich
in Fe & Mg
Module BP 11 - 04
Density-pressure inside the Earth
15
6000
Radius (km)
4000
2000
6000
0
400
Gravity (m s – 2)
10
300
200
5
mantle
5
0
0
Thursday, 12 November 2009
outer
core
2000
4000
Depth (km)
outer
core
inner
core
inner
core
6000
100
0
0
2000
4000
Depth (km)
6000
0
Pressure (GPa)
Density (103 kg m– 3 )
10
mantle
R. Bousquet 2009-2010
0
Radius (km)
4000
2000
Hard solid
Solid
Hard solid
Crust
29
R. Bousquet 2009-2010
Lithosphere
Thursday, 12 November 2009
Asthenosphere
Liquid
Solid
Inner
Core
km
gT&P
51
00
increasi
n
00
km
Outer
Core
upper
mantle
10
0-2
0
65
0- 0
70
km m
k
0
Module BP 11 - 04
Physical state
due to increasing
T and P with Depth
Lower
mantle
Module BP 11 - 04
Isothermen in der Erde
“Real” geotherm
1000
400 km
13
670 km
24
GP
a
GP
a
Mantle
2000
135
3000
outer core
2900 km
GP
a
4000
5000
329
5100 km
GP
a
inner core
6000
R. Bousquet 2009-2010
1000 2000 3000
Lithosphere
Thursday, 12 November 2009
4000 5000
Asthenosphere
6000
Geotherm if the heat tranfer is
only due to the conduction
Module BP 11 - 04
Model of the Earth
CONTINENT
LITHOSPHERE
rigid
100–150 km thick
OCEAN
Crust
38–40 km thick
Crust
6–8 km thick
UPPER
MANTLE
0
220
400
670
MESOSPHERE
(LOWER MANTLE)
semi-solid, plastic
Depth
(km)
2891
R. Bousquet 2009-2010
OUTER
CORE
fluid
Thursday, 12 November 2009
5150
CORE
rigid
6371
LITHOSPHERE
rigid
70–100 km thick
ASTHENOSPHERE
partially molten
phase
transition
olivine
–> spinel
phase
transition
spinel
–> oxides,
perovskite
Module BP 11 - 04
Description of the Earth: the crust
CONTINENT
LITHOSPHERE
rigid
100–150 km thick
OCEAN
Crust
38–40 km thick
Crust
6–8 km thick
UPPER
MANTLE
0
220
400
670
MESOSPHERE
(LOWER MANTLE)
semi-solid, plastic
Depth
(km)
2891
OUTER
CORE
fluid
5150
CORE
rigid
R. Bousquet 2009-2010
6371
Thursday, 12 November 2009
LITHOSPHERE
rigid
70–100 km thick
ASTHENOSPHERE
partially molten
phase
transition
olivine
–> spinel
phase
transition
spinel
–> oxides,
perovskite
Oceanic crust: 0.099% of Earth's
mass; depth of 0-10 kilometers
The oceanic crust contains 0.147% of
the mantle-crust mass. The majority of
the Earth's crust was made through
volcanic activity. The oceanic ridge
system, a 40,000-kilometer network of
volcanoes, generates new oceanic
crust at the rate of 17 km3 per year,
covering the ocean floor with basalt.
Hawaii and Iceland are two examples
of the accumulation of basalt piles.
Continental crust: 0.374% of Earth's
mass; depth of 0-50 kilometers.
The continental crust contains 0.554%
of the mantle-crust mass. This is the
outer part of the Earth composed
essentially of crystalline rocks. These
are low-density buoyant minerals
dominated mostly by quartz (SiO2)
and feldspars (metal-poor silicates).
The crust (both oceanic and
continental) is the surface of the Earth;
as such, it is the coldest part of our
planet. Because cold rocks deform
slowly, we refer to this rigid outer
shell as the lithosphere (the rocky or
strong layer).
0
Depth (km)
Module BP 11 - 04
Description of the Earth: the crust
0
5
10
P-wave velocity (km s– 1)
2
4
6
8
Generalized petrological model
and P-wave velocity–depth profile
for oceanic crust
ocean bottom
ocean
crust
~ 7 km
thick
Moho
15
0
top of
basement
Depth (km)
oceanic sediments
Layer 2
basalt
Layer 3
gabbro
ultramafics
Generalized petrological model
and P-wave velocity–depth profile
for continental crust
near-surface
low-velocity layer
10
R. Bousquet 2009-2010
Layer 1
upper mantle
P-wave velocity (km s– 1)
4
6
8
sea water
Cenozoic sediments
Mesozoic & Paleozoic
sediments
20
Conrad
laminations
30
Thursday, 12 November 2009
Moho
zone of positive
velocity gradient
sialic low-velocity layer
middle crustal layer
upper crystalline basement
granitic laccoliths
migmatites
high-velocity tooth
amphibolites
lower crustal layer
granulites
uppermost mantle
ultramafics
Module BP 11 - 04
Description of the Earth: the upper mantle
CONTINENT
LITHOSPHERE
rigid
100–150 km thick
OCEAN
Crust
38–40 km thick
Crust
6–8 km thick
UPPER
MANTLE
0
220
400
670
MESOSPHERE
(LOWER MANTLE)
semi-solid, plastic
Depth
(km)
2891
OUTER
CORE
fluid
5150
CORE
rigid
R. Bousquet 2009-2010
6371
Thursday, 12 November 2009
LITHOSPHERE
rigid
70–100 km thick
ASTHENOSPHERE
partially molten
phase
transition
olivine
–> spinel
phase
transition
spinel
–> oxides,
perovskite
Upper mantle: 10.3% of Earth's mass;
depth of 10-400 kilometers
The upper mantle contains 15.3% of
the mantle-crust mass. Fragments
have been excavated for our
observation by eroded mountain belts
and volcanic eruptions. Olivine (Mg,Fe)
2SiO4 and pyroxene (Mg,Fe)SiO3 have
been the primary minerals found in
this way. These and other minerals are
refractory and crystalline at high
temperatures; therefore, most settle
out of rising magma, either forming
new crustal material or never leaving
the mantle. Part of the upper mantle
called the asthenosphere might be
partially molten.
Module BP 11 - 04
Description of the Earth: the upper mantle
0
P-wave velocity (km s–1)
6 7
8 9 10 11
0
crust
lid
600
1000
Thursday, 12 November 2009
upper mantle
400 km
discontinuity
400
800
R. Bousquet 2009-2010
low-velocity layer
670 km
discontinuity
lower mantle
Depth (km)
200
5
10
Epicentral distance, 6 ($)
15
20
25
30
35
40
Mineral Composition 2
R. Bousquet 2009-2010
Module BP 11 - 04
Description of the Earth: the upper mantle
Thursday, 12 November 2009
R. Bousquet 2009-2010
Module BP 11 - 04
Description of the Earth: the upper mantle
Phase Transformation
Olivine undergoes pressure dependent transformation to the
spinel structure (Ringwoodite), and then breaks down to
Perovskovite.
The transformations correlate with the major seismic
discontinuities, and probably generate part of the Signal.
Thursday, 12 November 2009
Module BP 11 - 04
Description of the Earth: the upper mantle
€
€
R. Bousquet 2009-2010
€
Olivine Phases
(Mg,Fe) 2 SiO4 = (Mg,Fe) 2 SiO4
Olivine
Wadsleyite
Pressure 13-14 GPa
410 km.
(Mg,Fe) 2 SiO4 = (Mg,Fe) 2 SiO4
Wadsleyite
Ringwoodite
Pressure 18 GPa.
520 km.
(Mg,Fe) 2 SiO4 = (Mg,Fe)SiO3 + (Mg,Fe)O
Ringwoodite
Peroskovite
Magnesiowüstite
Thursday, 12 November 2009
Pressure 23 GPa.
660 km.
Module BP 11 - 04
Description of the Earth: the upper mantle
Mineralogy of the mantle:
influence of the chemical composition
60
Perovskite (Pv)
+
Magnesiowüstite (Mw)
1400
50
1200
Pressure (GPa)
40
Pv + Mw
+ St
1000
2 Magnesio-­
wüstite (Mw)
+
Stishovite (St)
30
800
a + Pv
+ Mw
600
20
a + Mw
+ St
`-­Phase (`)
Spinel (a)
` + a 400
_ + a 10
_ + ` 200
R. Bousquet 2009-2010
Olivine (_)
0
0
0.8
Mg2SiO4
Thursday, 12 November 2009
0.6
0.4
Composition
0.2
1
Fe2SiO4
Module BP 11 - 04
Description of the Earth: transition zone
CONTINENT
LITHOSPHERE
rigid
100–150 km thick
OCEAN
Crust
38–40 km thick
Crust
6–8 km thick
UPPER
MANTLE
0
220
400
670
MESOSPHERE
(LOWER MANTLE)
semi-solid, plastic
Depth
(km)
2891
OUTER
CORE
fluid
5150
CORE
rigid
R. Bousquet 2009-2010
6371
Thursday, 12 November 2009
LITHOSPHERE
rigid
70–100 km thick
ASTHENOSPHERE
partially molten
phase
transition
olivine
–> spinel
phase
transition
spinel
–> oxides,
perovskite
Transition region: 7.5% of Earth's
mass; depth of 400-650 kilometers
The transition region or mesosphere
(for middle mantle), sometimes called
the fertile layer, contains 11.1% of the
mantle-crust mass and is the source of
basaltic magmas. It also contains
calcium, aluminum, and garnet, which
is a complex aluminum-bearing
silicate mineral. This layer is dense
when cold because of the garnet. It is
buoyant when hot because these
minerals melt easily to form basalt
which can then rise through the upper
layers as magma.
Module BP 11 - 04
Description of the Earth: transition zone
Pyroxene - Garnet Phases
Transformation of non-olivine
components are also important (30%).
This phase changes are gradual and lead
to changes of slope of velocity.
Pyroxene starts to dissolve into the
garnet
Structure at 350 - 500 km.
R. Bousquet 2009-2010
At about 580 km CaSiO3 perovskovite
Exsolves from garnet.
Thursday, 12 November 2009
Module BP 11 - 04
Description of the Earth: the lower mantle
CONTINENT
LITHOSPHERE
rigid
100–150 km thick
OCEAN
Crust
38–40 km thick
Crust
6–8 km thick
UPPER
MANTLE
0
220
400
670
MESOSPHERE
(LOWER MANTLE)
semi-solid, plastic
Depth
(km)
2891
OUTER
CORE
fluid
5150
CORE
rigid
R. Bousquet 2009-2010
6371
Thursday, 12 November 2009
LITHOSPHERE
rigid
70–100 km thick
ASTHENOSPHERE
partially molten
phase
transition
olivine
–> spinel
phase
transition
spinel
–> oxides,
perovskite
Lower mantle: 49.2% of Earth's mass;
depth of 650-2’890 kilometers
The lower mantle contains 72.9% of
the mantle-crust mass and is probably
composed mainly of silicon,
magnesium, and oxygen. It probably
also contains some iron, calcium, and
aluminum. Scientists make these
deductions by assuming the Earth has
a similar abundance and proportion of
cosmic elements as found in the Sun
and primitive meteorites.
D": 3% of Earth's mass; depth of
2’700-2’890 kilometers
This layer is 200 to 300 kilometers
(125 to 188 miles) thick and
represents about 4% of the mantlecrust mass. Although it is often
identified as part of the lower mantle,
seismic discontinuities suggest the D"
layer might differ chemically from the
lower mantle lying above it. Scientists
theorize that the material either
dissolved in the core, or was able to
sink through the mantle but not into
the core because of its density.
Module BP 11 - 04
Description of the Earth: the outer core
CONTINENT
LITHOSPHERE
rigid
100–150 km thick
OCEAN
Crust
38–40 km thick
Crust
6–8 km thick
UPPER
MANTLE
0
220
400
670
MESOSPHERE
(LOWER MANTLE)
semi-solid, plastic
Depth
(km)
2891
OUTER
CORE
fluid
5150
CORE
rigid
R. Bousquet 2009-2010
6371
Thursday, 12 November 2009
LITHOSPHERE
rigid
70–100 km thick
ASTHENOSPHERE
partially molten
phase
transition
olivine
–> spinel
phase
transition
spinel
–> oxides,
perovskite
Outer core: 30.8% of Earth's mass;
depth of 2,890-5,150 kilometers
The outer core is a hot, electrically
conducting liquid within which
c o n v e c t i v e mo t i o n o c c u rs . Th i s
conductive layer combines with
Earth's rotation to create a dynamo
effect that maintains a system of
electrical currents known as the
Earth's magnetic field. It is also
responsible for the subtle jerking of
Earth's rotation. This layer is not as
dense as pure molten iron, which
indicates the presence of lighter
elements. Scientists suspect that about
10% of the layer is composed of sulfur
and/or oxygen because these elements
are abundant in the cosmos and
dissolve readily in molten iron.
Module BP 11 - 04
Description of the Earth: the inner core
CONTINENT
LITHOSPHERE
rigid
100–150 km thick
OCEAN
Crust
38–40 km thick
Crust
6–8 km thick
UPPER
MANTLE
0
220
400
670
MESOSPHERE
(LOWER MANTLE)
semi-solid, plastic
Depth
(km)
2891
OUTER
CORE
fluid
5150
CORE
rigid
R. Bousquet 2009-2010
6371
Thursday, 12 November 2009
LITHOSPHERE
rigid
70–100 km thick
ASTHENOSPHERE
partially molten
phase
transition
olivine
–> spinel
phase
transition
spinel
–> oxides,
perovskite
Inner core: 1.7% of the Earth's mass;
depth of 5,150-6,370 kilometers
The inner core is solid and unattached
to the mantle, suspended in the
molten outer core. It is believed to
have solidified as a result of pressurefreezing which occurs to most liquids
when temperature decreases or
pressure increases.
Module BP 11 - 04
Comparison of the different planets
The internal structure of the terrestrial planets are similar. They all have
Core – High density metal
Mantle – Medium density rocky materials, such as silica (SiO2), hot, semi-solid
Crust – lowest density rocks, such as granite and basalt (black lava rock…)
The layering of different density materials occurs due to differentiation – heavy
materials sink to the bottom while lighter material rise to the top…
R. Bousquet 2009-2010
Lithosphere: The coolest and most rigid layer of rock near a planet’s surface.
Molten lava of Earth exists at a very narrow region beneath the
lithosphere
Thursday, 12 November 2009
R. Bousquet 2009-2010
Module BP 11 - 04
A nother view of the Earth
Thursday, 12 November 2009
Module BP 11 - 04
Origin of the Geoid : density anomalies
Geoid over India
R. Bousquet 2009-2010
Blue=low gravity
Red = high gravity
Seismic tomography in the mantle
Blue=“cold”=“more dense”
Red = “hot” = “less dense”
It is very clear that long wavelength Geoid lows are associated to cold
and dense material in the mantle. Therefore :
Long wavelength Geoid = density anomalies in the mantle
short wavelength Geoid = surface topography (i.e. mountains)
Thursday, 12 November 2009
Mittelozeanischer
Rücken
Kontinentale
Rift Zone
Aktiver
Kontinentalrand
Ozean. Insel
Tiefe
km
0
Kruste
Spinell
Granat
phäre
os
phäre
os
100
1000°C
3,5
Li
As
the th
n
Module BP 11 - 04
Summary of the structure of the Earth
Basalt
Su
7,0
SpinellPeridotit
n
tio
uk
bd
200
300
Grenat + Pyroxen
Majorit
Oberer Mantel
400
Olivin
Phasen-Übergang
Spinell Phase
13
GranatPeridotit
500
Druck
GPa
600
Temperatur
Spinell Phase
Phasen-Übergang
R. Bousquet 2009-2010
700
Thursday, 12 November 2009
24
2000°C
Perowskit + Magnesiowüstit
Unterer Mantel
2900
Post-Perowskit
Phasen-Übergang
Eisen+ Nickel + geringe Anteile
flüssig
leichterer Elemente
5080
Kern
fest
verändert nach STOSCH (2002)
4000°C