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Possible Paths of Earthquake Waves

Description
Earth’s Interior

Most of our knowledge of Earth’s interior comes from the study of P and S earthquake waves
Travel times of P and S waves through Earth vary depending on the properties of the materials
S waves travel only through solids

Layers based on physical properties
Crust
Thin, rocky outer layer
Varies in thickness
Roughly 7 km (5 miles) in oceanic regions
Continental crust averages 35–40 km (22–25 miles)
Exceeds 70 km (40 miles) in some mountainous regions

Layers based on physical properties
Crust
Continental crust
Upper crust composed of granitic rocks
Lower crust is more akin to basalt
Average density is about 2.7 g/cm3
Up to 4 billion years old

Layers based on physical properties
Crust
Oceanic Crust
Basaltic composition
Density about 3.0 g/cm3
Younger (180 million years or less) than the continental crust

Layers based on physical properties
Mantle
Below crust to a depth of 2900 kilometers (1800 miles)
Composition of the uppermost mantle is the igneous rock peridotite (changes at greater depths)

Layers based on physical properties
Outer Core
Below mantle
A sphere having a radius of 3486 km (2161 miles)
Composed of an iron-nickel alloy
Average density of nearly 11 g/cm3

Layers based on physical properties
Lithosphere
Crust and uppermost mantle (about 100 km thick)
Cool, rigid, solid
Asthenosphere
Beneath the lithosphere
Upper mantle
To a depth of about 660 kilometers
Soft, weak layer that is easily deformed

Layers based on physical properties
Mesosphere (or lower mantle)
660–2900 km
More rigid layer
Rocks are very hot and capable of gradual flow
Outer core
Liquid layer
2270 km (1410 miles) thick
Convective flow of metallic iron within generates Earth’s magnetic field

Layers based on physical properties
Inner Core
Sphere with a radius of 1216 km (754 miles)
Behaves like a solid
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