Delhi Earthquake

Subject: Geography

Context:

Recently, eleventh minor earthquake recorded in and around Delhi since May, the most powerful of which happened to be of magnitude 3.4.

Concept:

The Earth’s crust consists of seven large lithospheric plates and numerous smaller plates. These plates move towards each other (a convergent boundary), apart (a divergent boundary) or past each other (a transform boundary).

Earthquakes are caused by a sudden release of stress along faults in the earth’s crust. The continuous motion of tectonic plates causes a steady build-up of pressure in the rock strata on both sides of a fault until the stress is sufficiently great that it is released in a sudden, jerky movement. The resulting waves of seismic energy propagate through the ground and over its surface, causing the shaking we perceive as earthquakes.

Types of Earthquake:

Tectonic Earthquakes

Earthquakes caused by plate tectonics are called tectonic quakes. They account for most earthquakes worldwide and usually occur at the boundaries of tectonic plates.

Induced Earthquakes

Induced quakes are caused by human activity, like tunnel construction, filling reservoirs and implementing geothermal or fracking projects.

Volcanic Earthquakes

Volcanic quakes are associated with active volcanism. They are generally not as powerful as tectonic quakes and often occur relatively near the surface. Consequently, they are usually only felt in the vicinity of the hypocenter.

Collapse Earthquakes

Collapse quakes can be triggered by such phenomena as cave-ins, mostly in karst areas or close to mining facilities, as a result of subsidence.

Seismic Zones:

• According to the macro seismic zoning map of entire India, the Bureau of Indian Standards has classified the entire country into four major groups — Zone V (high intensity) to Zone II (low intensity).
• Around 30% of Delhi falls under Zone V, while the rest is under Zone IV.
• The Delhi-NCR region is very peculiar with regard to seismic activities. It has several faultlines that generate earthquakes, but it also feels the impact of quakes that are epicentred as far as the Hindukush mountains in Afghanistan and even in Nepal.
• Even a strong earthquake in the Himalayan belt may pose a threat to Delhi-NCR. The fact is that this region is only 150-odd km from the active Himalayan seismic belt. Also, the large sediment thickness (loose soil) in the Ganga Alluvial Plains to the north of Delhi tends to amplify the impact of earthquakes.