In this article, you will read about Earthquakes, their causes, earthquake waves and their types, and major earthquake zones in India. This article is very important for exams conducted by UPSC, PSCs and other state level boards.
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Earthquakes
An earthquake is a sudden shaking or trembling of the Earth’s surface caused by the movement of tectonic plates or volcanic activity thereby releasing energy.
The point of origin of earthquake is called ‘Focus’ or hypocentre. It is inside the earth.
The point on the Earth’s surface vertically above the focus is called ‘Epicentre’.
The waves of an earthquake are detected and recorded by seismograph and the magnitude of waves is measured on Richter’s scale .
The magnitude on Richter scale is measured on a scale 0 to 10. Each increase of one unit on the Richter scale represents a tenfold increase in earthquake strength.
No earthquake has been measured above 9 on scale.
Earthquake intensity is measured on the modified Mercalli scale, which ranges from 0 to 12 depending upon the intensity.
The region around the Pacific Ocean is prone to earthquakes. In India, Himalayan region and Ganga-Brahmaputra valley are prone to earthquakes.
The world’s greatest earthquake belt is Circum Pacific Belt and it is found along the rim of the Pacific Ocean, where about 81 percent of our planet’s largest earthquakes occur. It is famously known as “Pacific ring of fire”.
Types of earthquake waves
There are three types of earthquake waves. They are;
1. Primary waves (P waves)
- Primary waves are longitudinal waves.
- They from the point of happening by the displacement of surrounding particles.
- They are transmitted through solids, liquids and gases.
- These wave travel the fastest among all the earthquake waves, and are therefore the first ones to reach the surface.
- These waves travel in the speed range of 5-13 km/s.
2. Secondary waves (S waves)
- These waves are transverse waves.
- These travel through solids only.
- S waves can’t pass through core, as it contains molten material.
- These waves are almost 1.7 times slower than P waves.
P waves and S waves are actually the body waves as they are generated due to the release of energy at the focus and move in all directions traveling through the body of the earth.
3. Long Waves or Long Period Waves (L waves)
- When body waves interact with surface rocks, a new set of waves is created. These waves are known as surface waves and propagate across the earth’s surface.
- Long waves waves are a type of surface waves.
- These waves travel on Earth’s surface.
- These waves cause maximum destruction.
- Long waves are called so as they cover the greatest distances of any seismic wave.
Effects of Earthquake
- Ground shaking
- Differential ground settlements
- Mud slides
- Soil liquefaction
- Ground sunking
- Avalanches
- Fires
- Tsunami
The Earthquake Zones in India
On the basis of intensity of the earthquakes, a map of India has been published by the Meteorological Department in collaboration of the Indian Standard Institution.
The map shows the five seismic zones based on modified Mercalli scale.
- Zone I:- It is a very low intensity earthquake zone. It experiences feeble and slight earthquakes.
- Zone II:- It is a low intensity earthquake zone. It experiences strong earthquakes.
- Zone III:- It is a moderate intensity earthquake zone. It experiences very strong earthquakes.
- Zone IV:- It is a severe intensity zone, and it experiences very destructive earthquakes.
- Zone V:- it is a very severe intensity earthquake zone. It experiences very disastrous and catastrophic earthquakes.
Region Wise Distribution of India in Earthquake Zones
| Zone | Region |
|---|---|
| Zone I | No area of India is currently falling in zone I |
| Zone II | Southern Punjab and Haryana, certain parts of Plains of Uttar Pradesh, Eastern Rajasthan, Coastal areas of Odisha and Tamilnadu. |
| Zone III | Southern and South Eastern parts of Rajasthan, larger parts of Madhya Pradesh, Maharashtra, Karnataka, Jharkhand and Northern and North Western parts of Orissa. |
| Zone IV | Jammu and Kashmir, Himachal Pradesh, Northern parts of Punjab, Haryana, Delhi, Eastern Uttar Pradesh, Tasai and Bhabhat regions, the Himalayan areas of Uttaranchal, Bihar and Sikkim. |
| Zone V | Certain parts of Jammu and Kashmir, Himachal Pradesh, Uttranchal, Monghy, and Darbhanga districts of Bihar, Northern part of India and Kutchh region of Gujarat. |
So, this was all about the earthquakes, their causes, earthquake waves and earthquake zones of India. We are sure that you will find this very useful.