Introduction
Residents of Delhi and surrounding areas were jolted awake by strong tremors from an earthquake of magnitude 4.0 on the Richter scale. Despite the relatively low magnitude, the intensity of the tremors was significant, leading many to rush out of their homes in panic. Fortunately, there were no reports of casualties or damage to properties. However, this raised a crucial question—why did a moderate earthquake cause such strong tremors in the national capital?
Understanding Earthquake Magnitudes and Tremors
In general, earthquakes below 2.5 magnitude are not felt by people, and those between 2.5 to 5.4 magnitude usually cause only minor tremors without structural damage. A 4.0 magnitude earthquake is considered moderate and unlikely to cause severe damage. However, several factors contribute to the intensity of tremors felt on the surface, such as depth, location, and local geological conditions.
Key Reasons Behind Strong Tremors in Delhi
1. Epicentre Located in Delhi
One of the primary reasons for the strong tremors was that the epicentre of the earthquake was within Delhi itself. According to seismologists, the intensity of an earthquake is most strongly felt near its epicentre. The quake, which struck near Dhaula Kuan, caused intense shaking because the seismic energy was released directly beneath the city. This area has experienced minor tremors in the past, with a 3.3 magnitude earthquake recorded in 2015 and a 4.7 magnitude tremor in 2007.
2. Shallow Depth of the Earthquake
The earthquake originated at a shallow depth of about 5 km below the surface. Shallow earthquakes tend to cause more noticeable shaking compared to deeper ones because the seismic energy has less distance to travel before reaching the surface. The US Geological Survey (USGS) explains that high-frequency vibrations from shallow earthquakes create a short-period seismic wave motion that can lead to a booming sound, intensifying the perception of the quake’s impact.
3. Dense Urban Infrastructure
Delhi’s dense urban infrastructure also played a role in amplifying the tremors. Seismic waves travel faster in areas with heavy construction, as buildings and other structures act as conduits for the energy, causing vibrations to be felt more intensely. Skyscrapers, high-rise apartments, and closely packed residential complexes contribute to the amplification of tremors in urban settings.
4. Delhi’s Seismic Vulnerability
Delhi is located in Seismic Zone IV, which is classified as a high-risk zone for earthquakes. The Delhi Disaster Management Authority states that earthquakes in this zone generally range between magnitudes 5 to 6, with occasional occurrences of even stronger quakes. The national capital is also at risk due to its proximity to the Himalayan fault lines, where the Indian tectonic plate is colliding with the Eurasian plate. This tectonic activity continuously builds pressure, which is periodically released in the form of earthquakes.
5. Plate Tectonics and Seismic Activity
The seismicity of North India, particularly in Delhi, is driven by the ongoing collision between the Indian plate and the Eurasian plate. This movement causes the plates to bend and store energy, similar to a compressed spring. When the built-up energy is suddenly released due to plate slippage, it results in an earthquake. Since Delhi is located on an alluvial plain with soft soil, seismic waves can be amplified, increasing the intensity of shaking.
Why Did People Hear a Booming Sound?
Many residents reported hearing a loud rumbling noise during the quake. The USGS explains that shallow earthquakes often generate high-frequency vibrations that reach the surface quickly, creating a sound wave that is audible. This phenomenon is similar to sonic booms produced by fast-moving objects in the air. The closer the epicentre to the surface, the louder the sound that accompanies the shaking.
What Experts Say
According to the National Centre for Seismology (NCS), there is no cause for alarm. Minor earthquakes are a natural occurrence in seismic zones, and aftershocks are expected but will likely be of lesser magnitude.
A senior NCS official stated:
“Delhi has been experiencing minor earthquakes. This earthquake occurred in Dhaula Kuan. In 2007, an earthquake of 4.7 magnitude had occurred there. There is nothing to worry about. It is a seismic zone there… The earthquake occurred due to in-situ material heterogeneity. After a 4.0 magnitude quake, the aftershock will be 1.2 magnitudes less. It is natural as the ground adjusts itself.”
Precautionary Measures for Future Earthquakes
Despite the reassurances from experts, Delhi residents should remain prepared for potential seismic activity. Some essential safety measures include:
- Developing an Emergency Plan: Households should have a clear action plan in case of a significant earthquake, including evacuation routes and emergency contacts.
- Securing Heavy Objects: Tall furniture and heavy household items should be securely fastened to prevent falling during tremors.
- Creating an Emergency Kit: A kit containing essentials like bottled water, non-perishable food, first aid supplies, and flashlights should be kept handy.
- Identifying Safe Spots: Residents should identify safe areas in their homes, such as under sturdy tables or near interior walls, to take cover during an earthquake.
- Staying Informed: Monitoring updates from seismological agencies and disaster management authorities can provide critical information on earthquake risks and safety measures.
Conclusion
The 4.0 magnitude earthquake in Delhi felt much stronger than expected due to multiple factors, including its shallow depth, the location of its epicentre, and the city’s dense infrastructure. While there was no reported damage, the tremors served as a stark reminder of Delhi’s vulnerability to seismic activity. As a city located in Seismic Zone IV, preparedness and awareness are crucial in mitigating risks associated with future earthquakes.
