Crust6-7 km/sec

Mantle8-13 km/sec

Outer Core8-10 km/sec Inner Core

10-11 km/sec

P-wave Velocitie

s

€

VP =K + 4

3 GD

€

VS = GD

K = bulk modulus = resistance of material to squeezing

G = shear modulus = resistance of material to shearing

D = density

€

VP =K + 4

3 GD

€

VS = GD

Seismological Results

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

€

VP =K + 4

3 GD

€

VS = GD

G = 0for 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/sspeed of light in glass = 200,000,000 m/s

From: www.what-is-the-speed-of-light.com

Slow

SlowFast

Fast

M=7.8, ∆=62°

Magnitude 7.8 TARAPACA, CHILE, June 13, 2005 22:45 UTC

Boston, Massachusetts - First Wave Arrives 22:55 (10 minutes)

Distanced measured in degrees from epicenter.

Travel-time versus Distance

M=7.6, ∆=97°

Boston, Massachusetts - First Wave Arrives 4:04 (13 minutes)

Magnitude 7.6 PAKISTAN, October 08, 2005 at 03:51 UTC

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

Tra

vel T

ime

6371 km

1

2

3

Path Distance (km) Time (sec) Velocity

1 2,758 360 7.7 km/sec 2 6,563 600 10.9 km/sec 3 9,543 780 12.2 km/sec

Crust6-7 km/sec

Mantle8-13 km/sec

Outer Core8-10 km/sec Inner Core

10-11 km/sec

P-wave Velocitie

s

Crust6-7 km/sec

Mantle8-13 km/sec

Outer Core8-10 km/sec Inner Core

10-11 km/sec

P-wave VelocitiesAir: 0.3

Water: 1.4Concrete: 3.6Granite: 5.5-6.0Iron: 5.8Aluminum: 6.6

T

Distanced measured in degrees from epicenter.

Travel-time versus Distance Curves

Distanced measured in degrees from epicenter.

Travel-time versus Distance Curves

P-wave reflected from Core-Mantle Boundary

PcP

FastSlow

“Moho”Andrija Mohorovicic

Zagreb Seismological Observatory1909

“Moho”Andrija Mohorovicic

Zagreb Seismological Observatory1909

Slow

Fast

Slow

Fast

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 Earthby Press, Siever, Grotzinger and Jordan (2004).

Mechanism of Plate Tectonics

Crust6-7 km/sec

Mantle8-13 km/sec

Outer Core8-10 km/sec Inner Core

10-11 km/sec

P-wave Velocitie

s

Variations in seismic velocity (+/- a few percent) are depicted by warm (low velocity) or cool (high velocity) colors.

Seismic Tomography

Seismic Tomography