Delhi’s Earthquake Vulnerability and Recent Tremors

Delhi-NCR experienced earthquake on Monday morning, shaking the region awake. The National Centre for Seismology reported the quake at 5:36 AM IST, with its epicentre at Dhaula Kuan. Despite a 4.0 magnitude, the tremors felt stronger due to its shallow depth of 5 km and proximity to populated areas. Experts indicated that the quake was not caused by plate tectonics but rather by local geological conditions.

About Earthquake Magnitude and Depth

Earthquakes are measured on the Richter scale, which gauges their magnitude. A 4.0 magnitude is considered moderate. The depth of an earthquake influences how it is felt. Shallow earthquakes, occurring at depths less than 10 km, produce stronger surface shaking. This is because seismic waves have less distance to travel before reaching the surface.

Geological Factors in Delhi’s Seismic Activity

Delhi’s vulnerability to earthquakes stems from its geographical location. It lies near the collision zone of the Indian and Eurasian Plates. The Indian Plate moves northward, creating stress along fault lines. Delhi is classified in Seismic Zone IV, indicating a high risk of moderate to strong earthquakes.

Active Fault Lines Affecting Delhi

Delhi is impacted by several fault systems. The Himalayan Seismic Belt includes the Main Central Thrust and the Main Boundary Thrust, which can generate powerful earthquakes. The Delhi-Haridwar Ridge is another critical fault that contributes to intra-plate tremors. The Aravalli-Delhi Fault System has also been responsible for previous seismic events.

Soil Composition and Seismic Amplification

Much of Delhi is built on soft alluvial soil. This soil type amplifies seismic waves, causing moderate tremors to feel stronger and inflicting more structural damage. In contrast, regions with stable rocky terrain experience less amplification.

Historical Earthquake Activity in Delhi

Delhi has a history of earthquakes. Notable events include the 1720 Delhi Earthquake and the 2015 Nepal Earthquake, both felt strongly in the region. The accumulation of tectonic stress in the Himalayas raises concerns about the possibility of a major earthquake in the future.

Preparedness and Mitigation Strategies

Experts warn of the risk of a powerful earthquake (greater than 8.0 magnitude) in the Himalayas. To mitigate potential damage, recommendations include retrofitting older buildings and enforcing stricter seismic codes. Improved earthquake preparedness is essential for reducing risks associated with future seismic events.

Seismic Zones Explained

Seismic zones categorise geographical areas based on their earthquake risk. India is divided into four zones, with Zone II being the least risky and Zone V the most. Delhi falls under Zone IV, indicating a high probability of seismic activity.

Future Seismic Risks in Delhi

The accumulation of tectonic stress along the Himalayan fault system suggests that a major seismic event is overdue. While local tremors may not directly correlate to this risk, they highlight Delhi’s vulnerability to larger earthquakes.

Questions for UPSC:

1. Critically discuss the impact of soil composition on seismic wave amplification in urban areas.
2. Examine the geological factors contributing to Delhi’s classification as a high-risk seismic zone.
3. Estimate the potential consequences of a major earthquake in the Himalayas on the Delhi-NCR region.
4. Point out the historical earthquakes that have impacted northern India and their magnitudes.

Answer Hints:

1. Critically discuss the impact of soil composition on seismic wave amplification in urban areas.

1. Soft alluvial soil, common in urban areas like Delhi, amplifies seismic waves more than rocky terrain.
2. This amplification can make moderate tremors cause structural damage.
3. Buildings on softer soil may sway more, increasing the risk of collapse during earthquakes.
4. Soil type influences the intensity of shaking felt by residents, leading to panic and evacuation.
5. About soil composition is crucial for urban planning and earthquake preparedness strategies.

2. Examine the geological factors contributing to Delhi’s classification as a high-risk seismic zone.

1. Delhi is located near the collision zone of the Indian and Eurasian Plates, leading to tectonic stress.
2. It is classified in Seismic Zone IV, indicating a high probability of moderate to strong earthquakes.
3. Active fault systems, like the Himalayan Seismic Belt and the Aravalli-Delhi Fault System, contribute to seismic risk.
4. Local geological conditions, such as “in situ material heterogeneity,” can trigger intra-plate earthquakes.
5. The ongoing movement of the Indian Plate exacerbates the potential for seismic activity in the region.

3. Estimate the potential consequences of a major earthquake in the Himalayas on the Delhi-NCR region.

1. A major earthquake (>8.0 magnitude) could cause widespread destruction in densely populated areas of Delhi-NCR.
2. Infrastructure damage could lead to loss of life and economic disruption.
3. Amplification effects from soft soil could exacerbate the impact, making tremors feel stronger.
4. Emergency services may be overwhelmed, complicating rescue and recovery efforts.
5. Preparedness measures, such as retrofitting buildings and enforcing stricter codes, are essential to mitigate risks.

4. Point out the historical earthquakes that have impacted northern India and their magnitudes.

1. The 1720 Delhi Earthquake, estimated at ~7.5 magnitude, caused damage in the region.
2. The 1803 Mathura Earthquake, also ~7.5 magnitude, was felt strongly in Delhi.
3. The 1905 Kangra Earthquake, with a magnitude of 7.8, had widespread effects across northern India.
4. The 2015 Nepal Earthquake, recorded at 7.8 magnitude, caused panic and tremors in Delhi.
5. Recent events, like the 2023 Nepal Earthquake (6.4 magnitude), further highlight the region’s seismic activity.