Delhi Earthquake - Rau's IAS

Context: Recently, Delhi witnessed an earthquake of 4.1 magnitude, and the epicenter being within Delhi raised concerns.

Relevance of the topic:

Prelims: Questions based on geographical phenomena related to earthquakes.

Mains: Detailed question on Indian earthquake risk zones, vulnerabilities and preparedness.

About Delhi Earthquake

Delhi witnessed an earthquake of 4.1 magnitude. As per National Center of Seismology it was the strongest earthquake to have originated in Delhi in the past five years.
How is this earthquake different from previous ones?
- Epicenter: Previous earthquakes had an epicenter away from Delhi, like Afghanistan and Nepal. This time the earthquake originated within Delhi near Dhaula Kuan region.
- Shallow depth: The earthquake had a shallow focus of about 5 km below the surface.
- Peculiar sound: The earthquake was reported to have a low-frequency sound produced due to the passing of vibrations and shaking of material. Such sounds are observed when the epicenter is shallow. The high-frequency seismic vibrations generate short-periodic vibrations in the air above the surface leading to a sound, which is often referred to as the earthquake boom.

Aravalli-fold: Delhi lies on the Aravalli-Delhi fold belt which is a seismically-active geological belt extending from southern and eastern Rajasthan to Haryana and Delhi.
Presence of deformed rocks: The possibility of earthquakes is intensified due to the presence of deformed layers of rocks that have folded or bent due to geological processes hundreds of millions of years ago.
Alluvial soil: Delhi is dominated by the alluvial soil type that has high potency to transfer the vibrations without much loss of energy. Therefore, the presence of alluvial soil adds to the earthquake’s intensity.
Proximity to the risk zones: Delhi is located near the Himalayan seismic belt, one of the world’s highest risk zones for the earthquake. The Himalayas lie at the active convergent boundary between the Indian plate and the Eurasian plate.

Delhi falls in earthquake Zone IV due to following vulnerabilities:

Geographical vulnerabilities: Delhi’s location is near Aravalli-fold and High risk seismic zones like Himalayas. Also, the domination of alluvial soil makes Delhi vulnerable for the earthquake led disaster.
Infrastructural vulnerabilities: Delhi is a densely populated location, also most of the infrastructure of Delhi is colonial and obsolete. These closely placed buildings and lack of seismic resistant buildings contribute to the vulnerability of earthquake led disaster.
Demographic vulnerability: Delhi is a prime destination for migration contributing to the resource burden and poverty. Persistent migration and lack of resources leads to the slum proliferation. Slums and unsafe constructions due to encroachments also enhance the vulnerability of Delhi.

Zonation: The Geological Survey of India has identified and zoned the various earthquake regions based on their risks and vulnerabilities.
BIS standards: The Bureau of Indian Standards has released the detailed guidelines for material and construction in various zones of India. (On the basis of recommendations of BIS and Gujarat earthquake, India has reduced earthquake zones from five to four, removing the Zone I)
International efforts: India has founded the Coalition of Disaster Resilient Infrastructure (CDRI) to foster the investment and technological collaboration among the nations to enhance preparedness.

Earthquake (EQ) is any sudden shaking of the ground caused by the passage of seismic waves through Earth’s rocks.
Seismic waves are vibrations generated by an earthquake, explosion, or similar energetic source and propagated within Earth or along its surface. Earthquakes generate four principal types of elastic waves:
- Body waves (P and S) travel within Earth.
- Surface waves (Love and Rayleigh) travel along its surface.
Focus: Point of origin of the vibrations below the surface of the earth.
Epicenter: Point on the Earth's surface directly above a hypocenter or focus, the point where an earthquake or an underground explosion originates.
Magnitude of EQ: It is a measure of the size or amplitude of the seismic waves generated by an earthquake source and recorded by seismographs. It is measured by the Richter Scale from 0 to 10.
Intensity of EQ: Intensity measures the strength of shaking produced by the earthquake at a certain location and its impact. It is measured by the Mercalli scale and Medvedev-Sponheuer-Karnik (MSK) scale.

Read More: Earthquake Waves & Shadow Zones