Earthquakes : Causes, Types and Prevention

Earthquakes

When tremor is felt on the surface of the earth due to some external or internal factor or endogenous force, it is called earthquake. It is also called earthquake in common language. By the way, the root cause of earthquake is the collision of tectonic plates. As a result of this collision, internal energy is suddenly released in the lithosphere of the earth, due to which seismic waves are generated on the surface of the earth and sudden vibrations are felt. These tremors or earthquakes are so destructive, that in a moment they can destroy the city of the city. It can arise due to both human and natural reasons. According to Reed's 'Elastic-Reinforcement Theory' - every rock has a capacity to bear stress. After that if the tension force becomes more, then the rock breaks and the broken part comes back to its place. In this way, there are incidents of faults in the rock and due to their colliding with each other, earthquakes occur.

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Important Points

• Before an earthquake, there is an increase in the amount of radon gases in the atmosphere. Therefore, the increase in the amount of this gas in a particular region or region indicates the occurrence of an earthquake in that particular region or region.
• The study of earthquakes is called seismology.
• Office of the National Center for Seismology in India – located at IMD Headquarters, Lodhi Road, New Delhi, which compiles, analyzes and stores data related to it.

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Tsunami

Tsunami is a word of Japanese language, which means – sea waves coming on the coast. These are very long and low vibrational sea waves generated in the oceans by oceanic earthquakes. They have nothing to do with tidal waves. Tsunami waves are accompanied by water movement throughout the depth, so they are more catastrophic. In the open oceans, the height of these waves is less, about one meter, while in the coastal area, there is a sudden increase in their height, due to which there is terrible destruction in a short time. | Their speed is very high, which can be up to 650 km / h or even more. The Tsunami Warning System is located at the Indian National Center for Ocean Information Services (INCOIS), Hyderabad.

Cause of the Earthquake

There are mainly two factors for the occurrence of earthquakes –

1. Artificial or Man-Made Factors
2. Natural Factor

Internal Structure Of The Earth

1. Artificial or Man-Made Factors

At present, the most important factor of earthquake is human activities, under which roads, dams, huge reservoirs etc. are being constructed by humans in tectonically unstable regions. | Apart from this, nuclear tests conducted in oceans, deserts or other deserted places are also a major cause of earthquake. Military exercises conducted by the armies of different countries can also be a big reason, because during this time many types of ammunition and missiles are also tested.

2. Natural Factor

In the natural cause, the endogenous force working inside the earth is the main reason, under which vertical movement, horizontal movement force come. Compression force and tension force under the horizontal movement force are one of the main causes of earthquake. Apart from this, volcanic activity, land balancing, faulting etc. are important.

Major Earthquake Glossary

1. Focus or Hypo-center - The place from where the occurrence of earthquake starts or the rocks break, as a result of which seismic waves are generated, it is called Focus or Hypo-center.
2. Epicenter – The place where seismic waves are first experienced is called Epicenter. Or the place where the line connecting the center of the earth to the center of the earthquake intersects the surface of the earth is called epicentre.
3. Elastic Energy – The internal energy coming out of the earthquake core is called elastic energy.
4. Isoseismal Lines – The lines joining places of equal seismic intensity are called Isoseismal Lines.
5. Homoseismal Lines – Lines joining places in an area where earthquakes are experienced simultaneously. These are called Homoseismal Lines.

Types of Earthquake

On the basis of the depth of the earthquake core, it is mainly divided into three parts, which are as follows –

1. Normal Earthquake – In this, the depth of the place of origin ranges from 0 to 50 km. Most of the earthquakes are of normal type and their depth is around 25 km.
2. Intermediate earthquake – In this, the depth of the place of origin varies from 50 to 250 km.
3. Deep Earth Earthquake – In this, the depth of the place of origin ranges from 250 to 700 km.

Earthquake Measuring Instrument

A sensitive instrument called seismograph or seismograph is used to measure the intensity of an earthquake. It has three scales, which are as follows –

• Marcelli - This is a measurement qualitative scale, not quantitative. There are a total of 12 parameters in this, which are based on the experience of our senses.
• Richter Scale – This is a mathematical measure, which is based on the energy of an earthquake. In this, the number of measurements is between 0 to 9. In this, each next unit exhibits 10 times more intensity than its previous unit. At present, using this scale, the intensity of an earthquake is calculated.
• Raciferal – In this the number of scales is from 1 to 11.

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Types of Seismic Waves

During an earthquake, many types of seismic waves emerge, which move in different directions. These are mainly of three types –

• Primary Waves or Long Waves or P Waves
• Secondary Waves or Transverse Waves or S Waves
• Surface Waves or L Waves

1. Primary Waves or Long Waves or P - Waves 

These are longitudinal waves, which travel like sound waves. The speed of these waves in a liquid medium is less than in a solid medium. This wave has the highest speed among all the three known waves. The speed of these waves is 66% more than S waves.

2. Secondary Waves or Transverse Waves or S - Waves

These are transverse waves, which move like light waves. It runs only in solid medium. They disappear in liquid medium. Therefore, they cannot pass through the core of the earth. Their speed is 40% less than P waves.

3. Surface Waves or L - Waves

These are the most powerful waves, which cover the longest path. They affect only the upper part of the earth. Their speed is very slow and they reach the most late. These waves can also pass through water. Their speed is 5 km/sec. In these, the speed of vibration is maximum. Due to zigzag movement, it is most destructive.

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Earthquake Prevention Measures

To prevent earthquake, it is necessary to follow the safety measures and guidelines given by the National Disaster Management Authority. Apart from keeping the necessary emergency kit always ready at home by the authority, guidelines have been given for rescue after earthquake, which are as follows –

Rescue Emergency Kit

• Battery operated torches and spare batteries
• battery operated radios
• First Aid Kits and Manuals
• Essential medicines
• Emergency food – dry items and drinking water – packaged and sealed
• Candle and match in waterproof container
• Knife 
• Chlorine tablets and powdered water purifiers
• Cain opener
• Cash money and ATM card
• Aadhar card or your identity card
• Thick ropes and cords
• Strong shoes

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Measures to be Taken After Earthquake

• After an earthquake, keep yourself calm and listen to the instructions and guidelines given on TV and radio and follow them.
• Stay away from the sea coast and the lower banks of the river.
• Turn off the water, gas and electricity switches.
• Be ready for the tremors of the coming earthquake.
• Do not light matches, cigarettes or lighters. Do not turn on the switch. Because gas leakage or short circuit can happen after an earthquake. Use a torch for illumination.
• If flammable material has been spilled on the ground, clean it immediately.
• Avoid going to places where power lines have been damaged. Do not touch the objects that come in contact with the wires.
• Get out or get away from damaged homes and buildings. Do not enter them. Leave the house with essential medicines and supplies.
• If there is a fire somewhere, try to extinguish it. Inform the fire brigade if necessary.
• If someone is seriously hurt, don't move them unless they are in danger.
• The water kept in the vessel should be filtered with a cloth or strainer and drink it.

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