Seismic Waves of Earth

Seismic Waves of Earth

Seismic waves created during the earthquakes. There are two

types of seismic waves and they are body waves and surface waves.

1. Body Waves: These types of waves can travel through the

earth's interior. Body waves are of two types  P waves (Primary waves)

and S waves (Secondary waves).

• P waves: This wave is a longitudinal wave. The P waves

        are the fastest of all seismic waves. It can pass through the

        solid rocks and fluids. In air it travels nearly at the speed of

        sound. We can feel the bump and rattle of the wave.

• S waves: This wave is transverse in nature. This wave is

        slower than the P wave and it can only travel through solid

        rocks.

2. Surface Waves: This wave can only move along the surface

of the planet. The surface waves are slower than the seismic body

waves. There are two types of surface waves, rayleigh waves and

love waves.

• Rayleigh waves: This wave rolls on the ground just like

        waves rolls across the water.

• Love wave: It is the fastest surface wave.

We know that the earth's layers are made of different materials.

These materials are different by their physical and chemical

properties, such as temperature, density, etc. The compositions

vary with layers. The seismic rays help to detect the composition

of different layers of the earth. The rays behave differently when

they pass through various materials, and we can detect the materials. 

The geological region where one layer changes to another is called

the transition zone. In the transition zone, we can see the changes

in composition also. Sometimes abrupt changes in physical

properties can be seen in the earth's interior. This geological

region is called discontinuity.

Conrad Discontinuity: This discontinuity lies between upper

and lower crust.

Mohorovičić discontinuity (Moho): This discontinuity is

located between the crust and the mantle layer.

Repetti Discontinuity: It is located between the upper and

the lower mantle. The velocity of the seismic wave increases

sharply in this region.

Gutenberg Discontinuity: This discontinuity is located

between the lower mantle and the outer core. At this depth the

primary seismic wave (P wave) decreases and the secondary

seismic wave (S wave) disappears completely. 

Lehmann Discontinuity: It is located between the inner core

and the outer core. The velocity of the P wave and S wave increase.