Disasters and Disaster Management – Sendai Framework, Floods, Cyclones, etc.

Earthquake in Afghanistan

Note4Students

From UPSC perspective, the following things are important :

Prelims level : Earthquakes

Mains level : Read the attached story

Recently a powerful earthquake of magnitude 5.9 on the Richter scale struck a remote town in Afghanistan, killing over a thousand and injuring many more.

How do earthquakes happen?

  • According to the theory of plate tectonics, the Earth’s crust and upper mantle are made of large rigid plates that can move relative to one another.
  • Slip on faults near the plate boundaries can result in earthquakes.
  • The point inside the Earth where the earthquake rupture starts is called the focus or hypocentre.
  • The point directly above it on the surface of the Earth is the epicentre.

What are Seismic Waves?

  • Any elastic material when subjected to stress, stretches in a proportional way, until the elastic limit is reached.
  • When the elastic limit is crossed, it breaks.
  • Similarly, the Earth also has an elastic limit and when the stress is higher than this limit, it breaks.
  • Then there is a generation of heat, and energy is released. Since the material is elastic, the energy is released in the form of elastic waves.
  • These propagate to a distance determined by the extent of the impact. These are known as seismic waves.

Why Earthquake in Afghanistan?

  • Afghanistan is earthquake-prone because it’s located in the mountainous Hindu Kush region, which is part of the Alpide belt — 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.
  • Additionally, 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.

How are earthquakes measured?

  • Earthquakes are measured by seismographic networks, which are made of seismic stations, each of which measures the shaking of the ground beneath it.
  • In India, the National Seismological Network does this work.
  • It has a history of about 120 years and its sensors can now detect an earthquake within five to ten minutes.

Issues with Earthquake measurement

  • Everywhere, the wave parameters are measured, not the total energy released.
  • There is a direct relationship between the quantum of energy released and the wave amplitude.
  • The amplitude of the wave is a function of the time period of the wave.
  • It is possible to convert the measured wave amplitude into the energy released for that earthquake.
  • This is what seismologists call the magnitude of the earthquake.

What is the Richter magnitude scale?

  • This is a measure of the magnitude of an earthquake and was first defined by Charles F. Richter of the California Institute of Technology, U.S., in 1935.
  • The magnitude of an earthquake is the logarithm of the amplitude of the waves measured by the seismographs.
  • Richter scale magnitudes are expressed as a whole number and a decimal part, for example 6.3 or 5.2.
  • Since it is a logarithmic scale, an increase of the whole number by one unit signifies a tenfold increase in the amplitude of the wave and a 31-times increase of the energy released.

How are zones designated?

  • Based on seismicity, intensity of earthquakes experienced, and geological and tectonic qualities of a region, countries are divided into several zones.
  • In India, for example, there are four zones, designated Zone II-Zone V. Among these, Zone V is the most hazardous and Zone II the least hazardous.

Can we predict Earthquakes?

  • Since parameters of the earthquake are unknown, it is near impossible to predict an earthquake.
  • The problem with earthquakes is that they are heavily dependent on the material property, which varies from place to place.
  • If there are elastic waves propagating through a material, there are two kinds of waves — the primary wave which reaches first, and the second one called the secondary wave, which is more destructive.
  • If it is known that the amount of energy released is extremely high, trains and power grids can be shut down and the damage minimised.
  • This has worked in some locations, but not on a large commercial basis.

Successful attempts made so far

  • The most successful early warning systems are in Japan.
  • They have several hundreds of thousands recording devices.
  • Responses are sent to a central point where they estimate whether it is large enough to form a tsunami or some other hazard, and precautionary steps are taken.

 

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