Context:

A magnitude 4.0 earthquake struck Delhi on February 17, 2025, with its epicenter near Dhaula Kuan, highlighting the city's ongoing earthquake risk. Delhi lies in Seismic Zone IV, meaning it is a high-risk area for earthquakes. While it is not located on an active tectonic plate boundary, fault lines and geological factors contribute to its seismic activity.

Causes and Effects

Unlike Himalayan earthquakes caused by plate movements, the recent earthquake was an intra-plate event due to “in-situ material heterogeneity.” This occurs when differences in rock type, density, and fluid presence create stress in the Earth’s crust, leading to localized earthquakes.

Effects of In-Situ Heterogeneity on Faults:

·        Stress Accumulation: Variations in underground materials create pressure in fault zones, increasing earthquake chances.

·        Localized Tremors: These earthquakes do not involve major tectonic shifts but can cause strong shaking near the epicenter.

Fault Lines Affecting Delhi

Himalayan Seismic Belt

·        Though Delhi is far from the Himalayas, earthquakes from this region often affect the city.

·        Main Central Thrust (MCT) and Main Boundary Thrust (MBT) are key fault lines responsible for major Himalayan earthquakes.

·        Powerful quakes like the 1905 Kangra earthquake and the 2015 Nepal earthquake (both 7.8 magnitude) were strongly felt in Delhi.

Delhi-Haridwar Ridge & Aravalli Fault System

·        The Delhi-Haridwar Ridge extends beneath the city, making it prone to intra-plate earthquakes (those occurring within a tectonic plate rather than at plate boundaries).

·        The Aravalli-Delhi Fault System is a deep underground fault line responsible for past earthquakes in and around Delhi.

Indo-Gangetic Plain & Soil Amplification

Delhi sits on the Indo-Gangetic Plain, which consists of soft alluvial soil. Unlike hard rock, this soil amplifies earthquake waves, making tremors feel stronger and increasing the risk of structural damage.

Understanding Seismic Zones

A seismic zone indicates an area’s earthquake risk based on past activity and geological studies. India is divided into four seismic zones:

·        Zone II – Low risk

·        Zone III – Moderate risk

·        Zone IV – High risk (Delhi falls in this category)

·        Zone V – Highest risk

Being in Zone IV means:

·        Delhi has a high chance of strong shaking during an earthquake.

·        The expected earthquake intensity is around MSK-8, which means significant structural damage is likely.

·        Buildings in Delhi should be designed to withstand strong tremors.

Shallow Earthquakes and Their Impact

The National Center for Seismology reported that the Delhi earthquake occurred at a depth of 5 km, making it a shallow earthquake.

·        Shallow earthquakes (0-70 km depth) cause more damage because they release energy close to the surface.

·        Intermediate (70-300 km) and deep earthquakes (300-700 km) lose energy before reaching the surface, making their impact weaker.

Conclusion

Delhi’s dense population, aging buildings, and soft soil make it highly vulnerable to earthquakes. To reduce risks, strict building regulations, retrofitting old structures, earthquake awareness programs, and strong disaster response systems are essential. Proactive measures will help protect lives and infrastructure from future earthquakes.