discuss in detail about the structure of the Earth and the earthquake waves
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Answer:
Most of what we know about the interior of the Earth comes from the study of seismic waves from earthquakes. Seismic waves from large earthquakes pass throughout the Earth.
These waves contain vital information about the internal structure of the Earth. As seismic waves pass through the Earth, they are refracted, or bent, like rays of light bend when they pass though a glass prism.
Because the speed of the seismic waves depends on density, we can use the travel-time of seismic waves to map change in density with depth, and show that the Earth is composed of several layers.
The crust
This brittle outermost layer varies in thickness from about 25 to 70 km under continents, and from about 5 to 10 km under the oceans. Continental crust is quite complex in structure and is made from many different kinds of rocks.
Earth's mantle extends to a depth of 2,890 km, making it the thickest layer of Earth. The mantle is divided into upper and lower mantle. The upper and lower mantle are separated by the transition zone. The lowest part of the mantle next to the core-mantle boundary is known as the D″ (pronounced dee-double-prime[5]) layer. The pressure at the bottom of the mantle is ≈140 GPa (1.4 Matm). The mantle is composed of silicate rocks that are rich in iron and magnesium relative to the overlying crust. Although solid, the high temperatures within the mantle cause the silicate material to be sufficiently ductile that it can flow on very long timescales.
The average density of Earth is 5.515 g/cm3.[8] Because the average density of surface material is only around 3.0 g/cm3, we must conclude that denser materials exist within Earth's core. This result has been known since the Schiehallion experiment, performed in the 1770s. Charles Hutton in his 1778 report concluded that the mean density of the Earth must be about {\displaystyle {\tfrac {9}{5}}} {\tfrac {9}{5}} that of surface rock, concluding that the interior of the Earth must be metallic.
Most of what we know about the interior of the Earth comes from the study of seismic waves from earthquakes. Seismic waves from large earthquakes pass throughout the Earth.
These waves contain vital information about the internal structure of the Earth. As seismic waves pass through the Earth, they are refracted, or bent, like rays of light bend when they pass though a glass prism.
Because the speed of the seismic waves depends on density, we can use the travel-time of seismic waves to map change in density with depth, and show that the Earth is composed of several layers.
The crust
This brittle outermost layer varies in thickness from about 25 to 70 km under continents, and from about 5 to 10 km under the oceans. Continental crust is quite complex in structure and is made from many different kinds of rocks.
The mantle
Below the crust lies the dense mantle, extending to a depth of 2890 km. It consists of dense silicate rocks. Both P- and S-waves from earthquakes travel through the mantle, demonstrating that it is solid.
However, there is separate evidence that parts of the mantle behaves as a fluid over very long geological times scales, with rocks flowing slowly in giant convection cells.
The core
At a depth of about 2900 km is the boundary between the mantle and the Earth's core. The core is composed of iron and we know that it exists because it refracts seismic waves creating a 'shadow zone' at distances between 103º and 143º (see above diagram).
We also know that the outer part of the core is liquid, because S-waves do not pass through it.
Interactive Seismic Waves animation
The following interactive seismic waves viewer works with any HTML5 enabled web browser and allows users to follow seismic waves as they propogate through a draggable, spinnable cutaway globe.
