GS Paper 1
Syllabus: Important Geophysical Phenomena such as earthquakes
Direction: The article tries to explain the phenomenon of Earthquakes and earthquake risk in India.
Context: According to the Union Minister of State (independent charge) for S&T and Earth Sciences, around 60% of the landmass of India (covering all states) is prone to earthquakes of different shaking intensities.
- An earthquake is the shaking of the surface (occurs without warning) of the Earth resulting from a sudden release of energy in the Earth’s lithosphere that creates seismic waves.
- It is tectonic in origin and results from the release of accumulated stress of the moving lithospheric or crustal plates.
- The earth’s crust is divided into seven major plates (and several minor plates), which move slowly and continuously over the earth’s interior.
- Causes of earthquakes can be natural (tectonic, volcanic) and anthropogenic (mining activities, construction of dams, nuclear-chemical explosions).
- The occurrence of an earthquake in a populated area may cause numerous casualties and injuries as well as extensive damage to property.
Earthquake waves are basically of two types:
- Body waves: Generated due to the release of energy at the focus and move in all directions travelling through the body of the earth. There are two types of body waves.
|P-waves or ‘primary waves’
|S-waves or secondary waves
- Surface waves (most damaging): The body waves interact with the surface rocks and generate new sets of waves called surface waves, which move along the surface.
- Shadow zones: These are specific areas where the waves are not reported by seismograph.
- The earthquake events are scaled either according to the magnitude or intensity of the shock.
- The magnitude scale is known as the Richter scale (0-10), indicating energy released during the quake.
- The intensity scale is named after Mercalli (1-12), indicating the visible damage caused by the event.
The Earthquake Risk in India:
- India has been divided into four zones – II, III, IV and V – according to the seismic zoning map of India prepared by the Bureau of Indian Standards (BIS). Zone V is seismically the most active region, while Zone II is the least.
- Around 11% of the country falls in Zone V, 18% in Zone IV, 30% in Zone III and the remaining in Zone II.
Reasons for the Earthquake proneness in India:
- The Indian plate is driving into Eurasia at a rate of approximately 47 mm/year.
- Himalayan belt: Collision between Indo-Australian plate with Eurasian plate causes lots of strain in underlying rocks’ energy, which is released in the form of earthquakes.
- Andaman and Nicobar Islands: Seafloor displacement and underwater volcanoes disturb the equilibrium of earth’s surface.
- Deccan Plateau: The emergence of a fault line and energy build-up along the fault line of the river Bhima (Krishna) near Latur and Osmanabad (Maharashtra).
- Increasing population and unscientific land use for construction make India a high-risk land for earthquakes.
Q. Why are the world’s fold mountain systems located along the margins of continents? Bring out the association between the global distribution of Fold Mountains and the earthquakes and volcanoes. (UPSC 2014)