What is an Earthquake?
An earthquake is a natural phenomenon caused by the sudden release of energy within the Earth’s lithospheric crust, resulting in ground movement. This energy is released when tectonic plates—massive segments of the Earth’s lithosphere—move and interact with one another. Over time, stress builds up along plate boundaries. When it surpasses the strength of the rocks, fractures or faults occur, releasing seismic waves.
Types of earthquakes
- Tectonic earthquakes: The most common and destructive type, caused by the movement of tectonic plates.
- Volcanic earthquakes: Triggered by volcanic activity, these typically occur in regions with active volcanoes.
- Induced earthquakes: Caused by human activities such as mining, dam construction, and hydraulic fracturing (fracking).
How are earthquakes measured?
- Magnitude: The Richter scale measures an earthquake’s magnitude by quantifying the energy released at its source. Each whole number increase on this logarithmic scale corresponds to a tenfold increase in amplitude and approximately 31.6 times more energy release.
- Intensity: The Modified Mercalli Intensity (MMI) scale assesses the earthquake’s effects based on its impact on people, buildings, and the landscape.
Seismic zones of India
Due to its position at the boundary of the Indian and Eurasian tectonic plates, India is highly susceptible to earthquakes. The Bureau of Indian Standards (BIS) has classified the country into four seismic zones:
- Zone II: Low-risk region.
- Zone III: Moderate-risk zone.
- Zone IV: High-risk zone.
- Zone V: Very high-risk zone, comprising the most seismically active regions.
High-risk areas in India
- Zone V (Very high risk): Covers approximately 11% of India, including the northeastern states, Jammu and Kashmir, Himachal Pradesh, Uttarakhand, and the Rann of Kutch in Gujarat. These regions frequently experience seismic activity due to ongoing tectonic collisions.
- Zone IV (High risk): Covers around 18% of India, including Delhi, parts of Jammu and Kashmir, Himachal Pradesh, Bihar, and West Bengal. These areas are vulnerable due to active fault lines.
- Zone III (Moderate r): Covers 30% of India, including Kerala, Goa, Lakshadweep, and parts of Maharashtra and Gujarat.
- Zone II (Low risk): Encompasses the rest of the country with relatively lower seismic activity.
Delhi’s seismic vulnerability
Delhi falls within Seismic Zone IV, meaning it is at high risk of experiencing severe earthquakes. Several factors contribute to this vulnerability:
- Proximity to fault lines: Delhi is close to the Delhi-Hardwar Ridge and the Mahendragarh-Dehradun Fault, both of which are active seismic zones.
- Geological composition: The city is built on alluvial soil, which amplifies seismic waves, increasing the intensity of ground shaking.
- Urban density: Delhi’s high population density and rapid urbanisation make it highly susceptible to structural damage and casualties during a significant earthquake.
Historical earthquakes in Delhi
- 1720: A powerful earthquake caused widespread destruction in Delhi.
- 1803: Another major earthquake resulted in severe damage across the region.
- 2015: Tremors from the 7.8-magnitude Nepal earthquake were felt in Delhi, leading to mass panic and evacuations.
Earthquake preparedness and mitigation
Given its seismic risk, Delhi must adopt stringent earthquake preparedness measures, including:
- Strict Building codes: Implementing and enforcing earthquake-resistant designs in all new constructions.
- Retrofitting older structures: Strengthening existing buildings to withstand seismic forces.
- Public awareness campaigns: Educating people about emergency procedures and conducting regular earthquake drills.
- Enhanced emergency response systems: Establishing efficient disaster management protocols to ensure quick response and recovery.
While India’s seismic vulnerability is inevitable due to its geological positioning, proactive measures can significantly reduce earthquake-related damage and casualties. Stricter building regulations, improved early warning systems, and public awareness initiatives are crucial in mitigating future risks. The recent tremors in Delhi serve as a stark reminder of the urgent need for earthquake preparedness and sustainable urban planning.
