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.

Plate Tectonic Theory

  • This concept was formulated in the 1960s by Alfred Wegener. 
  • According to the theory, Earth has a rigid outer layer, known as the lithosphere, which is typically about 100 km (60 miles) thick and overlies a plastic (moldable, partially molten) layer called the asthenosphere
  • The lithosphere is broken up into:
    • seven very large continental- and ocean-sized plates,
    • six or seven medium-sized regional plates, and 
    • several small plates
  • These plates move relative to each other.
    • They typically move at rates of 5 to 10 cm (2 to 4 inches) per year, and interact along their boundaries.
    • They converge, diverge, or slip past one another. 
  • The continents are embedded in the plates and drift passively with them, which over millions of years results in significant changes in Earth’s geography.
  • Such interactions are thought to be responsible for most of Earth’s seismic and volcanic activity, although earthquakes and volcanoes can occur in plate interiors.

Source: TH

 
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