Question

Describe  the  types  of earthquake  waves.TNSCERT Class 7 Geography Ch1. The Earth -Its Structure and Tectonic movements

Answer 1

There are three types:
1)Primary waves
They are the first waves to be recorded on a seismogram of the earthquake.
In this the particles vibrate in the direction of movement of the wave, similar to the sound wave.They can pass through solids,liquids and gases.
2)Secondary waves or S waves
These waves are recorded after the Primary waves.In this the particles vibrate at right angles to the direction of movement of the wave.S waves travel through the earth's interior but cannot pass through liquids.
3)Surface waves or long waves
These waves travel along the surface of the earth and are recorded after the primary and S waves.

Answer 2

Earthquakes generate three types of seismic waves
 P (primary) waves, S (secondary) waves and surface waves, which arrive at seismic recording stations one after another.
Both P and S waves penetrate the interior of the Earth while surface waves do not. Due to this, P and S waves are known as "body waves".
Surface waves arrive last and are the least interesting to seismic tomographers because they don't penetrate deep inside the Earth, therefore provide little information about inaccessible terrain.