Natural Disasters


  • Earthquake is the sudden shaking of the ground caused by the passage of seismic waves through Earth’s surface.
  • Earthquakes generally happens when two blocks of the earth suddenly slip past one another along what is called the fault or fault plane.
  • The location below the earth’s surface where the seismic energy is released is called the hypocenter or focus.
  • While, the location directly above it on the surface of the earth is called the epicentre.
  • Magnitude of Earthquakes are recorded by instruments called seismographs on recordings called seismogram.

Types of Earthquakes

  • Earthquakes are divided into different types based on their cause. They are;

Tectonic earthquakes:

  • This is the most common type of earthquake and occurs in the fault lines along the plate boundaries.
  • The continuous motion of tectonic plates results in a steady build-up of pressure in the rock strata on both sides of a fault.
  • Tectonic Earthquakes are caused by a sudden release of stress along these faults in the earth’s crust.

Volcanic earthquakes:

  • Volcanoes are commonly found in areas where the crust is weak and in addition to that the mass of the volcano itself adds to the regional strain.
  • Hence when there is a sudden slip of rock masses adjacent to the volcano this results in a sudden release of elastic strain energy.
  • They are generally not as impactful as tectonic quakes and often occur relatively closer to the surface and hence are only felt in the vicinity of the hypocentre.

Anthropogenic Earthquake or Induced Earthquake

  • They are typically minor earthquakes and tremors which are caused by human activity which results in changes in the stresses and strains on the Earth’s crust.
  • Induced earthquakes can have multiple causes and can different levels of intensity.
  • When the roofs of underground mines collapse in areas of intense mining activity, causing minor tremors, they cause collapse earthquakes.
  • When the explosion of chemical or nuclear devices results in ground shaking they become known as explosion earthquakes.
  • The earthquakes that are created due to large reservoirs are referred to as reservoir induced earthquakes.