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An easy trick to learn the difference between P & S waves! UPSC Geography

Updated: Jul 19, 2021

Before we begin our blog today let us start from the basics as usual :

What is an Earthquake?

An Earthquake is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. This energy is released along the fault. Earthquake occurs when pressure from overlying rocks is greater than friction between two blocks. Fault : A fault is a fracture or zone of fracture between two blocks of rock. Faults allow the blocks to move relative to each other. This movement may occur rapidly, in the form of an earthquake - or may occur slowly, in the form of creep.

The energy travels in the form of waves. There are two types of waves - Body waves and Surface Waves. Body waves travel through the body (The lithosphere) in all directions. When body waves reach the surface and interact with the surface, Surface Waves are generated. They have higher amplitude & are more destructive. There are two types of Body waves - P and S waves. Let's understand the difference between the two: Difference between P and S waves : How to remember S waves characteristics: Associate everything with the S letter S Waves (Secondary Waves) a. S= Slow (They are travel slower than P waves ) b. S= Solid only ( They travel through Solid medium only) c. Method of propagation = Crest, and Trough (If you imagine it is a slanted S letter) d. S= Shadow zone of S waves is larger than P waves.

P waves (Primary Waves) a. Speed: They travel faster than S. P waves travel faster in Solid Medium and don't get deflected much. b. Medium: They travel through all Solid, Liquid, and Gas. c. Propagation: They travel through compression and rarefaction. Shadow Zones: Shadow zones are areas where waves are not reported.

a. Less than 105 degrees, both P&S waves are recorded. b. Between 105-145 degrees, No waves are recorded. c. Greater than 145 degrees only P waves are recorded. as they only could pass through solid medium and S waves could not pass. (We know that core of Earth is solid and hence S waves could not pass through it)

The outer core is a liquid is proved by the fact that : P waves are transmitted throughout the outer core

S waves are not transmitted throughout the outer core

P waves tend to decrease in velocity when they penetrate the outer core.


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P (Primary) Waves

S (Secondary) Wa

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