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Delhi Earthquake
Context
Delhi witnessed a 4.0-magnitude earthquake, which shook the region with a loud bang. This event has raised questions about why Delhi is prone to such tremors and the geological factors at play.
Why is Delhi Prone to Earthquakes?
- Delhi lies in Seismic Zone IV, an area with a moderate to high risk of earthquakes according to the Seismic Zoning Map of India.
- Seismic Zones are categorized based on earthquake risk:
- Zone V: High risk (earthquakes greater than magnitude 7).
- Zone IV: Moderate to high risk (earthquakes in the range of magnitude 5-6, occasionally up to magnitude 7-8).
- Zone III: Moderate risk.
- Zone II: Low risk.
- The Delhi-Haridwar Ridge, a major geological structure, and Delhi-Moradabad Faults pass through the region, making Delhi more susceptible to seismic activity.
- These lineaments have the potential to generate earthquakes of magnitude 6-7 and occasionally even 7-8.
The Seismicity of Delhi
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How Do Earthquakes Occur?
- Earthquakes happen due to the movement of tectonic plates, which form the Earth's crust.
- The Earth’s lithosphere (solid outer layer) is broken into large pieces called tectonic plates, which float on the semi-fluid mantle beneath them.
- When these plates move, they can cause stress on the Earth's crust.
- If the stress becomes too great, it results in faults (cracks in the Earth’s crust) along which the plates slide, releasing energy in the form of seismic waves, which causes an earthquake.
- Primary waves (P-waves): Fastest waves, travel through solids and liquids, and are the first to be detected.
- Secondary waves (S-waves): Slower than P-waves, only travel through solids and move perpendicularly.
- Surface waves: These are the slowest and most destructive waves, moving along the Earth's surface and causing the most damage.
- The point on the Earth's surface directly above where the earthquake begins is called the epicenter.
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