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Geography in Civil Services is one of the most chosen subject owing to its limited syllabus and interesting topics. ‘Earthquakes’ in Geography is among the most important sections generally asked in Civil Services. Candidates appearing for upcoming Civil Services exams are advised to go through the notes and important pointers mentioned in the article about pattern of IAS and it’s section.
Civil services examination is a nationwide competitive exam, conducted by union public service commission (UPSC) for recruitment to various Civil Services of the Government of India such as including the Indian Administrative Service (IAS) among others. The Civil Services Examination is considered to be one of the most difficult and competitive examinations in India. Only 50% of those who apply for the exam, appear for the preliminary. The examination consists of the following three stages:
Geography is a field of science which focuses on the study of the lands, the physical features, the inhabitants, and the phenomena of Earth. Earthquake is one of those natural phenomena of mother Earth. Let us study more on earthquakes.
Earthquake is a natural phenomenon which is caused by the release of sudden energy in the earth's lithosphere that creates seismic waves. These waves can cause shaking of ground and other experiences based on the frequency/power of the seismic waves.
The definition of an earthquake pretty much explains how an earthquake is caused. There are two main causes of an earthquake.
Seismograph: An instrument that measures and records details of earthquakes, such as force. (older term, New term Seismometer)
Focus/Hypocenter: The location where the earthquake begins. Origin of the earthquake, within the earth's crust.
Epicenter: The point on the earth's surface vertically above the focus of an earthquake.
Lithosphere: It is that rigid outer layer of the earth, consisting of the crust and upper mantle.
Earthquake is measured by a seismograph, which displays different types of waves caused by an earthquake. There are two types of waves:
A body wave is a seismic wave that moves through the interior of the earth and that is why it is called body waves. Body waves are faster than surface waves and hence they are the first to be detected on a seismograph. There are two types of body waves, primary waves, and secondary waves.
P wave A.K.A compressional wave is a seismic body wave that causes ground to shake back and forth in the same direction and the opposite direction as the direction the wave is moving. Primary waves are twice as fast as s-waves and are the first to reach during an earthquake. P- Waves are longitudinal, in which particle movement is in the same direction of wave propagation. They are the reason which create density differences in the earth material leading to stretching and squeezing.
Since they are slower than primary waves. They are second to arrive on the surface after P-Wave. . S- Waves can pass only through solid materials. This very property of s-waves led seismologists to conclude that the earth’s outer core is in a liquid state. (the entire zone beyond 105o from the epicenter does not receive S-waves). Secondary waves are transverse, in which directions of particle movement and wave propagation are perpendicular to each other.
A surface wave is a seismic wave that is trapped near the surface of the earth. Basically, when the body waves interact with surface rocks, it is called a surface wave. They create crests and troughs in the material through which they pass. Surface waves are considered to be the damaging waves. There are Two types of surface waves, Love waves and Rayleigh waves.
L- Wave is the kind of surface waves which causes horizontal shifting of the earth during an earthquake. They move in between of semi-infinite medium & an upper finite thickness. Love waves are much slower than body waves but are faster than Rayleigh.
The majority of ground shakes in an earthquake is due to the Rayleigh wave, which can be much larger than the other waves. These waves follow an elliptical motion & flow along the ground just like a wave flow across an ocean. That very flow, makes the ground move up and down and side-to-side in the same direction that the wave is moving.
Even though p-waves pass through all mediums, it causes reflection when it enters from one medium to another. The area where the seismograph records no waves is called as ‘shadow zone’ of that wave. Accordingly, it is observed that the area beyond 1050 does not receive S-waves and the area in between 1050 to 1400 does not receive P-waves.
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. The graphical representation which is recorded by seimometer/seisomograph is called seismogram. There are two main scales used in the seismometers:
Mercalli scale analysis the intensity of the earthquake by analyzing, by evaluating the damage done and the number of people felt it.
The scale represents the magnitude of the earthquake. The magnitude is expressed in absolute numbers from 1-10. Each whole number increase in Richter scale represents a ten times increase in power of an earthquake.
There are two well-defined belts where earthquakes frequently occur
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