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Lecture 20
Earth's Interior and Geophysical Properties
Lecture Outline
I Earth's Internal Structure
A)
B)
C)
The Crust
The Mantle
The Core
i.
ii.
Composition
Core-Mantle Boundary
IIIsostasy
III
Earth's Gravity
IV
Earth's Magnetic Field
A)
B)
V
VI
Magnetic Reversals
Magnetic Anomalies
Heat Within the Earth
Conclusions
Lecture 20
i
photo by John Galetzka, USGS
Geophysics
geophysics: the branch of earth
science which employs physical
measurements and mathematical
models to explore and analyze
the structure and dynamics of the
solid Earth and other bodies and
their fluid envelopes
Controls on Seismic Wave Velocity
pressure
composition of matter
state of matter
Controls on Seismic Wave Velocity
Pressure
Controls on Seismic Wave Velocity
Composition
Material Vp (ms-1) Density (gcm-3)
Salt
4.6
2.2
Quartz
6.1
2.7
Calcite
6.7
2.7
Dolomite
7.4
2.9
Siderite
7.0
4.0
Pyrite
8.4
5.0
Controls on Seismic Wave Velocity
State of Matter
Earth's Internal Structure
crust
mantle
core
Earth's Internal Structure
The Crust
Mohorovicic
Discontinuity
(Moho)
Earth's Internal Structure
Crustal Thickness
Earth's Internal Structure
Crustal Thickness (United States)
Earth's Internal Structure
The Composition of the Crust
Earth's Internal Structure
The Mantle
Earth's Internal Structure
The Mantle
Mantle is Solid (S waves propagate)
Mantle is Rigid (seismic waves propagate)
Mantle is Fluid (convection cells present)
Earth's Internal Structure
The Composition of the Mantle
Hofman
1988
Hart and Zindler
1986
Hutchinson
1974
SiO2
45.96
46.38
45.00
48.10
MgO
37.78
38.12
39.00
31.10
FeO
7.54
7.62
8.00
12.70
Al2O3
CaO
4.06
3.21
4.10
3.24
3.50
3.25
Mason
1966
3.10
2.30
Earth's Internal Structure
The Core
Size:
radius
volume
mass
3480 km (1/2 Earth)
1/8 Earth
1/3 Earth
Properties:
density
pressure
temperature
state
10-13 g/cm3
136-330 GPa
5500±1500 K
liquid-solid
Earth's Internal Structure
Composition of the Core
Iron
•
Nickel
•
~ 4%
Light Element (O or S) 10% by mass
•
Earth's Internal Structure
Major Discontinuities
crust/mantle - the MOHO
inside mantle (400 km and 670 km)
mantle/outer core (CMB)
outer/inner core (ICB)
Earth's Internal Structure
Major Discontinuities - The Moho
Earth's Internal Structure
The Core-Mantle Boundary
MAJOR Discontinuity
•
S-waves blocked by liquid outer core
•
Isostasy
the condition of equilibrium,
comparable to floating, of the
units of the lithosphere above
the asthenosphere.
Isostasy
Isostastic Adjustment
erosion and deposition
glacial rebound
crustal thickening
Isostastic Adjustment
Erosion and Deposition
Isostastic Adjustment
Glacial Rebound
Isostastic Adjustment
Crustal Thickening
Gravity
gravity: the attraction between two masses,
such as the Earth and an object on its
surface. Commonly referred to as the
acceleration of gravity (g).
Gravity
Gravity Anomaly
Gravity Anomaly
Gravity Anomaly
Gravity Anomaly
Earth's Magnetic Field
Earth's Magnetic Field
Rock Magnetism
Earth's Magnetic Field
Earth's Magnetic Field
Earth's Magnetic Field
Heat within the Earth
Heat within the Earth
Heat within the Earth
Sources of Earth's Heat
Pressure
Sunlight
Radioactive Decay
Primordial Heat
Redistribution of Earth's Heat
Radiation
Conduction
Convection
Redistribution of Earth's Heat
Conduction
Redistribution of Earth's Heat
Convection