# P and S waves moving through the Earth’s Interior.

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P and S waves moving through the Earth’s Interior

S and P waves are shock waves that are sent out as a result of an earthquake. These waves are similar to water waves Shock waves are created by a disturbance in an object and the shock of the disturbance creates waves, that also have wavelengths, amplitude, and frequencies.

The waves depend greatly on the composition that they are trying to pass through, which gives scientists a great deal of information about the interior of the Earth.

P waves travel fastest and are the first to arrive from the earthquake. In S or shear waves, rock oscillates perpendicular to the direction of wave propagation. In rock, S waves generally travel about 60% the speed of P waves, and the S wave always arrives after the P wave.

P waves, or primary waves, are the first type of waves to be felt at a considerable distance, and they travel very fast, more than 13,000 miles per hour.

Animation of P and S waves

We can use P and S waves and their characteristics to map the interior of the earth. Scientists deduced the structure of Earth's interior and how waves move through it by analyzing thousands of earthquakes recorded at Earth's surface.

densities density increases, seismic wave velocity increasesSeismic waves have helped scientists learn the various densities of the Earth's many layers because the speed of P waves moving through the earth generally increases with depth. This is because as density increases, seismic wave velocity increases.

P waves travel through the Earth's crust at an average of about four miles per second they reach an average of seven miles per second at the center of the Earth. suddenly shiftWhen the waves suddenly shift in direction and speed, scientists are able to determine the depths at which Earth's various layers are located.

P waves Can travel through solid rock and fluids their speed will vary depending on the density of the rock through which they travel increased speed will indicate increased density, thus providing information about the density and possible mineralogy of Earth's various layers.

The seismologists record the travel time it takes from the time the waves are released to the time it penetrates the other side. By triangulating these measurements, the seismologists can get a better understanding of the composition of what the waves are traveling through. The waves travel at a higher velocity when going through denser materials. By noting where the waves have considerable velocity changes, the seismologists can infer where the composition boundaries are, giving them the ability to map the interior of the Earth.

S waves cannot travel through fluids thus when an S-wave encounters the outer core of the Earth (liquid iron and nickel), it is disrupted the mantle outer core inner coreouter core 'shadow zone'This indicates the boundary between the mantle and outer core and the boundary between the inner core and outer core. The effect observed from the motion of S-waves reveals a 'shadow zone', opposite to where they originate.

Animation of P and S

video P and S waves and shadow zones in earths interior http://www.youtube.com/watch?v=yOGoK CK17a4&feature=related

Crust: A very thin, solid outer layer. The oceanic crust is about 3 miles thick. The continental crust is from 18–24 miles thick.

Moho: The boundary between the crust and the mantle.

Mantle: The layer beneath the crust. The mantle is about 1790 miles thick.

Upper mantle: Includes a solid layer fused to the crust. This layer combined with the crust is called the lithosphere. Beneath this is the asthenosphere, which is a partly molten layer. The asthenosphere is thought to be the layer upon which tectonic plates ride. The upper mantle is about 420 miles thick.

Lower mantle: Is composed of solid rock under conditions of extremely high temperature and pressure. This layer is about 1,370 miles thick.

Outer Core: A layer about 1,400 miles thick, having the properties of a metallic liquid.

Inner Core: A solid, metallic, spherical layer about 755 miles thick.

Earth Scientist at University discussing interior and P and S waves……first few min and skip to 21:53 to 23:10 min. http://www.youtube.com/watch?v=ve7N25R2h4c &feature=fvw http://www.youtube.com/watch?v=4nS10xNBfVE &feature=related shows seismic wave animationhttp://www.youtube.com/watch?v=4nS10xNBfVE &feature=related