Earth Structure and Plate Tectonics
Earthquakes and Earthquakes Waves
-Low- frequency pulses of energy generated by the forces that cause
- can spread rapidly into Earth in all directions and then return
to the surface.
- instruments that sense and record earthquakes
Some seismic waves—energy associated with earthquakes—can pass through earth.
Analysis of how these waves changed, and the time required for their passage, has told
researchers much about conditions inside our planet
A layered Earth
The uppermost layer of the earth is the lightweight, brittle, aptly names
, a heavy, dark-colored rock composed of
mostly oxygen, silicon, magnesium, and iron.
The most common material in the thicker
, a familiar
speckled rock composed mainly of oxygen, silicon, and aluminum.
, the layer beneath the crust, is though to consist mainly of oxygen, iron,
magnesium, and silicon.
The behavior of a rock is determined by three factors: temperature, pressure, and the rate
at which a deforming force (stress) is applied.
earth’s cool, rigid outer layer – is 100-200 KM in thickness. It comprises
the continental and oceanic crusts and the uppermost cool and rigid part of the mantle.
is the hot, partially melted, slowly flowing layer of upper mantle
below the lithosphere extending to a depth of about 150-659 KM
extends to the core. The asthenosphere and the mantle below the
asthenosphere have similar chemical composition. Although it is hotter, mantle below the
asthenosphere dot not melt because of the rapidly increasing pressure. As a result it is
more sense and flows much more slowly.