A P wave is commonly referred to as a pressure wave or a primary wave in the elastic body, also known as seismic waves. The study of such waves is called seismology. These waves travel through solid, liquid, and gas. These waves are known to travel faster than the other elastic seismic waves, which is why these waves are the first indication of an upcoming earthquake at a certain place.
When it is mentioned as a pressure wave, it is accountable for the alternating compression and rarefaction of that wave.
When it is mentioned as a primary wave, it is considered the first wave to be recorded by a seismograph. This is because this wave has a high velocity.
Movement of these waves:
This wave is also known to be a compressional wave due to its typical movement. It shakes the ground back and forth in the same and opposite direction of the movement of the wave. This particular movement is why an upcoming earthquake is recognized since these waves travel so strongly from the earth's interiors. These waves move through as well as around the earth.
There are mainly two kinds of seismic waves which are produced:
- Body waves- These types of waves are eligible to travel within the interiors of the earth. These waves have a higher frequency, so they are delivered first at the time of an earthquake. The P wave is the first type of body wave. These waves are able to travel through liquid as well as solid.
- Surface waves- These are the second type of waves emitted by an earthquake. However, these waves have a weaker frequency level than body waves, which is why this wave is not delivered immediately during an earthquake. In addition, this wave cannot travel within the internal parts of the earth. It can only move along the surfaces of the earth, meaning just the outermost part of the earth. They can only travel through solids. The first type of surface wave is called the Love wave.
Some basic properties of P waves are listed below:
- These are high-speed elastic waves which are also known as longitudinal waves.
- The vibrations and travel of these waves require a medium for propagation, just like sound waves.
- P wave originates from the first point where the earthquake has initially originated.
- All the other seismic waves that originate later in the process follow the pathway of the P wave.
- When these waves come across a surrounding filled with rocks, they undergo reflection and refraction.
- Other surroundings with any structural or physical layers are also responsible for the scattering and diffraction of these waves.
Factors determining the speed of Waves
P waves can travel through solids as well as liquid mediums. The following factors determine the speed of these waves while passing through different mediums:
- Compressibility of the material- The compressing power of the medium through which the wave is passing is important. It is necessary to see how much the material can be compressed into a smaller volume and then brought back to its original shape. The higher the compressing power of the material, the more the speed of these waves.
- The density of the material- The amount of mass that the material has per unit volume is also necessary for determining the speed of these waves. The availability of more mass restricts the flow of p waves as there is more disturbance. Therefore, the more the density of the material, the lesser will be the speed of P waves.
- The rigidity of the material- This is the last factor that affects the speed of the wave. The strength of the material to resist and refrain from being bent sideways or vertically and the strength to return to its straight self after the force stops acting on the material is an important factor. The more rigidity or strength the surface has, the more is the speed of these waves.
An analogy of P wave:
Take the thunder during stormy weather, for instance. The breakdown of a thunderstorm results in a big and clear clap of thunder. The tremendous noise produced makes the windows of your house move back and forth due to the sound waves hitting the surface. P waves also have a similar process of working.
These waves are extremely important as they are the only way to alert ourselves at the time of an earthquake. Therefore, they need a medium for travel and have some extraordinary features.