This is a social science video that answers
– What is an earthquake?
– How does an earthquake occur?
– What are the different types of waves?

An unexpected movement of the Earth's surface is called an earthquake. When two parts of the earth's surface suddenly move relative to each other along a fault line, due to tectonic forces, an earthquake occurs. A huge amount of energy is released in the form of tremors and vibrations, these earthquakes are called "tectonic earthquakes". The point of origin of an earthquake is called the focus, while the point directly above it on the earth's surface is called the epicenter. Due to the strong vibrations around the point of origin, the degree of destruction is greater around the epicenter. The branch of knowledge that deals with the study of earthquakes is called seismology, and experts who study seismic waves are called seismologists.
There are three types of seismic waves that propagate in all directions from the focus. These are P. S and L waves. Compression waves are the first to reach the seismic recording station because they propagate 1.7 times faster than shear waves and are therefore called "P" (primary) waves. ), while shear waves are called “S” (secondary) waves.
Primary waves cause rock particles to vibrate back and forth in the direction of the waves. Secondary waves, on the other hand, cause the particles to oscillate perpendicular to the direction of the waves. When P and S reach the Earth's surface, they are converted into long "L" waves that travel along the surface, vibrating horizontally at right angles to the direction of the waves called "love waves" or waves of Rayleigh, because they also move like Waves. The most violent shocks and subsequent destruction are caused by L waves.
While S waves cannot pass through liquids, P waves can pass through any medium. This helped seismologists learn more about the Earth's interior.
The instrument used to detect and record seismic waves is called a seismograph. The recorded material appears as a graph and is called a seismogram.
Based on the depth of their foci, earthquakes are classified into tree types. They are:
(a) Deep earthquakes that occur at depths greater than 300 km, the causes of which have not yet been identified.
(b) Intermediate focus earthquakes with focus depths between 55 and 300 km.
(c) Shallow earthquakes with depths less than 55 km.
The surface area of the Earth increases with focus depth, while intensity increases with decreasing focus depth.
To measure the magnitude of earthquakes, a Richter scale is used. The point scale is arranged in such a way that each of the units on the scale is equivalent to 30 times the energy released by the previous unit. While a magnitude of 2 is rarely felt, a magnitude of 7 indicates the lower limit of an earthquake having a devastating effect over a wide area.

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