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Document related concepts
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Transcript 
P-wave
Velocities
Mantle
8-13 km/sec
Outer Core
8-10 km/sec
Crust
6-7 km/sec
Inner Core
10-11 km/sec

K  43 G
VP 
D
G
VS 
D
K = bulk modulus
= resistance of material
to squeezing
D = density
G = shear modulus
= resistance of material
to shearing
Seismological Results
K G
VP 
D
4
3
G
VS 
D
Values of K, G and D at a given point
in the Earth’s interior.
Search for materials with appropriate
values of K, G and D
Estimates of composition of different
parts of the Earth’s interior

K G
VP 
D
4
3
G
VS 
D
G=0
for liquids
Outer Core of Earth
is liquid
From: Understanding Earth
by Press, Siever, Grotzinger
and Jordan
From: www.yorku.ca/eye/refract.htm
speed of light in a vacuum = 300,000,000 m/s
speed of light in glass = 200,000,000 m/s
From: www.what-is-the-speed-of-light.com
Slow
Fast
Fast
Slow
M=7.8, ∆=62°
Magnitude 7.8 TARAPACA, CHILE, June 13, 2005 22:45 UTC
Boston, Massachusetts - First Wave Arrives 22:55 (10 minutes)
Travel-time versus Distance
D
Distanced measured in degrees from epicenter.
M=7.6, ∆=97°
Magnitude 7.6 PAKISTAN, October 08, 2005 at 03:51 UTC
Boston, Massachusetts - First Wave Arrives 4:04 (13 minutes)
M=6.7, ∆=25°
Magnitude 6.8 CAYMAN ISLANDS, December 14, 2004 at 23:20 UTC
Boston, Massachusetts - First Wave Arrives 23:26 (6 minutes)
Distance
Travel Time
1
Path
2
6371 km
3
1
2
3
Distance (km)
2,758
6,563
9,543
Time (sec)
360
600
780
Velocity
7.7 km/sec
10.9 km/sec
12.2 km/sec
P-wave
Velocities
Mantle
8-13 km/sec
Outer Core
8-10 km/sec
Crust
6-7 km/sec
Inner Core
10-11 km/sec
P-wave Velocities
Air: 0.3
Water: 1.4
Concrete: 3.6
Granite: 5.5-6.0
Iron: 5.8
Aluminum: 6.6
Mantle
8-13 km/sec
Outer Core
8-10 km/sec
Crust
6-7 km/sec
Inner Core
10-11 km/sec
Travel-time versus
Distance Curves
T
D
Distanced measured in degrees
from epicenter.
D
Travel-time versus
Distance Curves
D
Distanced measured in degrees
from epicenter.
P-wave reflected from
Core-Mantle Boundary
PcP
Slow
Fast
“Moho”
Andrija Mohorovicic
Zagreb Seismological Observatory
1909
“Moho”
Andrija Mohorovicic
Zagreb Seismological Observatory
1909
Fast
Slow
Fast
Slow
Inner Core discovered by
Inge Lehmann in 1936
Copenhagen Seismological
Observatory
Inner Core discovered by
Inge Lehmann in 1936
Copenhagen Seismological
Observatory
Low Velocity Zone in Upper Mantle
Low Velocity Zone in Upper Mantle
Low Velocity Zone = Asthenosphere of Plate Tectonics
From Understanding Earth
by Press, Siever, Grotzinger and Jordan (2004).
Mechanism of Plate Tectonics
P-wave
Velocities
Mantle
8-13 km/sec
Outer Core
8-10 km/sec
Crust
6-7 km/sec
Inner Core
10-11 km/sec
Seismic Tomography
Variations in seismic velocity (+/- a few percent)
are depicted by warm (low velocity) or cool (high
velocity) colors.
Seismic Tomography
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