Earthquake and related Concepts( Part 1)- UPSC, State PCS , SSC etc.

What is an Earthquake:-

In very simple language, the earthquake is the shaking of the earth. An earthquake can be defined as a sudden violent shaking of the ground as a result of movements in the earth’s crust. These movements result in the release of energy and this releasing of energy causes this shaking and ultimately, Earthquake.


Causes of Earthquake:-  

Earth has a layered structure inside and the outermost hard rock-solid layer is called the Lithosphere which is formed by the combination of CRUST and UPPER UPPER Mantle. These are called TECTONIC PLATES. These plates are in continuous motion and they never rest. During their movement, these plates interact with each other.

Edges of the plates are called Boundaries and that edge where these boundaries interact is called Plate Boundaries.

Plate boundaries are not smooth, rather they are rough and nonlinear. When they move or slide past each other, they are locked with each other. The rest of the plate is still moving. Hence after a point, their lock is released and they also release a lot of energy which was earlier stored.

The energy radiates outward from the fault in all directions in the form of seismic waves like ripples on a pond. The seismic waves shake the earth as they move through it, and when the waves reach the earth’s surface, they shake the ground and anything on it, like our houses and us!

Points to remember:-

•  The point within the earth’s crust where an earthquake originates is called the focus or hypocenter or seismic focus.
• It generally lies within a depth of 6 km in the earth's crust.
• The point vertically above the focus on the earth’s surface is called the epicenter.
• The intensity of the earthquake will be highest in the epicenter and decreases as one moves away.
• All-natural earthquakes take place in the lithosphere

Measurement of Earthquake:- 

• Seismometers are the instruments which are used to measure the motion of the ground, which including those of seismic waves generated by earthquakes, volcanic eruptions, and other seismic sources.
• A Seismograph is also another term used to mean seismometer though it is more applicable to the older instruments.
• The recorded graphical output from a seismometer/seismograph is called a seismogram. (Note: Do not confuse seismograph with seismogram. A seismograph is an instrument while seismogram is the recorded output)

There are two methods/scales to measure earthquakes:-

(A) Intensity-based measurement/scales

1. MSK Scale -It is a macroseismic intensity scale used to evaluate the severity of ground shaking on the basis of observed effects in an area of the earthquake occurrence.  
2.  Marcalii Scale:-The scale represents the intensity of an earthquake by analyzing the after-effects like how many people felt it, how much the destruction occurred etc. The range of intensity is from 1-12.

(B) Magnitude Based Measurement/scale:-

odified Mercalli (MM)

Modified Mercalli (MM)

Modified Mercalli (MM)

Mercalli intensity sc

e usually provides ten or twelve grades of intensity starting with most feeble vibrations and goiMagnitude based measurement 

 1. Richter Scale:-  It is based on the amplitude of the the largest wave recorded on a specific type of seismometer and the distance between the earthquake and the seismometer.

 2. The Moment Magnitude Scale:- Unfortunately, many scales, such as the Richter scale, do not provide accurate estimates for large magnitude earthquakes So, .moment magnitude the scale is preferred. The moment magnitude scale is based on the total moment release of the earthquake. The moment is a product of  the distance a fault moved and the force required to move it

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