In Context
- Recently, an Earthquake of magnitude 6.1 struck a rural, mountainous region of eastern Afghanistan.
Causes of Earthquake in the region:
- Alpide belt:
- Afghanistan is earthquake-prone because it’s located in the mountainous Hindu Kush region, which is part of the Alpide belt.
- This belt is the second most seismically active region in the world after the Pacific Ring of Fire.
- The Alpide belt runs about 15,000 kilometers, from the southern part of Eurasia through the Himalayas and into the Atlantic.
- Along with the Hindu Kush, it includes a number of mountain ranges, such as the Alps, Atlas Mountains and the Caucasus Mountains.
- Converging plates:
- The Earth’s crust is especially lively in Afghanistan because it is where the Arabian, Indian and Eurasian tectonic plates meet.
- The boundary between the Indian and Eurasian plates exists near Afghanistan’s border with Pakistan.
- Recent earthquake formed when the Indian plate crashed violently with the Eurasian plate.
- Collisions like this shake and squeeze the ground upwards.
- Along with causing earthquakes, this movement creates mountains like the Himalayas or the Hindu Kush and Pamir mountain ranges in northeast Afghanistan.
Earthquake
- It is the shaking of the surface of the Earth which results in a sudden release of energy in the Earth’s lithosphere (rocky outer part of the Earth) that creates seismic waves.
- Earthquakes can cause severe damage, particularly in an area where homes and other buildings are poorly constructed and landslides are common.
- An earthquake’s point of initial rupture is called its hypocenter or focus.
- The epicentre is the point at ground level directly above the hypocenter.
- It is measured in the Richter scale.
Earthquake waves
These are of 2 types – body waves and surface waves
- Body waves:
- Generated due to the release of energy at the focus and move in all directions travelling through the body of the earth. Hence, the name – body waves.
- Travel only through the interior of the earth.
- Faster than surface waves.
- There are 2 types of body waves: P- primary waves and S-secondary waves.
- P waves travel through gaseous, liquid and solid materials whereas S waves travel only through solid materials.
- Surface Waves:
- When the body waves interact with surface rocks, a new set of waves is generated called surface waves.
- These waves move along the earth’s surface.
- Surface waves are transverse waves in which particle movement is perpendicular to the wave propagation. Hence, they create crests and troughs in the material through which they pass.
- They are the most damaging waves.
- 2 common surface waves are Love waves and Rayleigh waves.
- Speed of different Waves in descending order: Primary Waves > Secondary Waves > Love Waves > Rayleigh Waves.
- Shadow Zones:
- There exist some specific areas where the waves are not reported. Such a zone is called the ‘shadow zone’.
- A zone between 105° and 145° from the epicentre (approximately) is identified as the shadow zone for both the types of waves.
Indian Seismic Zones
- Earthquake-prone areas of India have been identified on the basis of 3 factors, namely:
- Scientific inputs related to seismicity.
- Earthquakes occurred in the past.
- Tectonic setup of the region.
- Based on these conditions, the Bureau of Indian Standards (BIS) divided the country into four seismic zones, viz. Zone II, Zone III, Zone IV and Zone V.
Plate Tectonic Theory
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Source: TH
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