Earthquake in Afghanistan

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.

Source: TH