Tremors in Delhi vs. Himalayan Earthquakes

Syllabus:

GS 1: Earthquakes

Why in the News?

A magnitude 4 earthquake struck Delhi near Dhaula Kuan, making it the strongest in five years. Delhi’s seismic activity and its location in Zone 4 highlight the need for earthquake preparedness and monitoring.

Tremors in Delhi vs. Himalayan Earthquakes

Earthquake in Delhi: A Rare Event

  • Delhi has experienced earthquakes before, but the one on Monday was different.
  • Most tremors in the city come from distant regions, such as Afghanistan or the Himalayas.
  • This time, the magnitude 4 earthquake originated within Delhi, near Dhaula Kuan.
  • It was the strongest earthquake to have originated in Delhi in the past five years.
  • A second earthquake of similar magnitude occurred in Siwan, Bihar, a few hours later.
  • Since magnitude 4 earthquakes are mild, no major damage was reported.

Seismic Activity in Delhi

  • Delhi lies in a seismically active region and is prone to earthquakes.
  • Several small earthquakes with magnitudes between 2 and 3 occur in and around the city regularly.
  • These minor quakes are usually detected only by seismometers.
  • According to the National Centre of Seismology, Delhi falls in Zone 4, a high-risk category in India’s earthquake hazard map.
  • Zone 4 regions are expected to experience MSK-8 level intensity during an earthquake.

Understanding MSK Intensity Scale

  • The MSK (Medvedev-Sponheuer-Karnik) scale measures earthquake intensity, not magnitude.
  • It assesses how an earthquake affects buildings and infrastructure.
  • Delhi’s classification under MSK-8 means it is prone to major structural damage.
  • The most earthquake-prone areas in India fall under Zone 5, which corresponds to MSK-9 or higher intensity.

Delhi’s Geology: Aravalli-Delhi Fold Belt

  • Delhi is part of the Aravalli-Delhi Fold Belt, a seismically active region stretching across Rajasthan, Haryana, and Delhi.
  • This belt consists of ancient deformed rock layers that have undergone folding due to geological processes over millions of years.
  • These deformations cause stress, which can sometimes be released as earthquakes.
  • Unlike the Himalayan region, where earthquakes are caused by tectonic plate collisions, the Aravalli-Delhi Fold Belt has slowed in activity over time.
  • Although less active today, some faults remain, leading to occasional mild quakes.

Comparing Earthquakes in Delhi and the Himalayas

  • Himalayan Earthquakes: Result from the Indian tectonic plate pushing under the Eurasian plate, building up stress that leads to major earthquakes.
  • Delhi’s Earthquakes: Caused by residual stress in the Aravalli-Delhi Fold Belt, leading to occasional mild tremors.
  • The Himalayan region experiences frequent high-magnitude quakes, while Delhi’s seismic activity is significantly weaker.

Frequency of Earthquakes in Delhi

  • On average, about 25 earthquakes of magnitude 5 or higher occur in and around Delhi annually.
  • Among these, around five earthquakes reach a magnitude of 5.
  • Most of these are too weak to be felt by people and are recorded only by seismometers.

Unusual Sound During the Earthquake

  • Many Delhi residents reported hearing a peculiar sound during Monday’s earthquake.
  • Earthquakes generate energy waves that travel through the Earth, causing vibrations.
  • These vibrations sometimes produce low-frequency sounds that are inaudible to humans.
  • Larger earthquakes may generate audible sounds, though this is rare.
  • Sounds associated with earthquakes are often mistaken for structural vibrations from buildings and infrastructure.

Historical Earthquakes in Delhi

  • Historical records mention a strong earthquake in Delhi around 1720.
  • Another major earthquake was reported in 1803, believed to have damaged Qutub Minar.
  • However, new research suggests that the 1803 earthquake likely originated in Srinagar-Devprayag (Uttarakhand) and was merely felt in Delhi.
  • Unlike the Himalayan region, Delhi has not witnessed truly destructive earthquakes in recent history.

Risk of a Major Earthquake in Delhi

  • Delhi has a history of seismic activity but lacks evidence of high-magnitude earthquakes.
  • Scientists believe that Delhi’s tectonic setup does not support large earthquakes.
  • The region does not have the necessary energy accumulation or stress required for a devastating quake.
  • However, if a major earthquake does occur in a nearby region like the Himalayas, Delhi could experience strong tremors.
  • The dense population and urban infrastructure make even moderate earthquakes potentially dangerous.

Earthquake Preparedness in Delhi

  • Given Delhi’s high seismic risk, it is crucial to implement earthquake-resistant construction practices.
  • Older buildings should be retrofitted to withstand tremors.
  • Public awareness campaigns should educate people on earthquake safety.
  • Emergency response plans should be strengthened to handle potential disasters.

Conclusion

Delhi experiences frequent mild earthquakes due to its location in the Aravalli-Delhi Fold Belt. While the risk of a major earthquake is low, preparedness, strict building regulations, and continuous seismic monitoring remain crucial for minimizing potential damage and ensuring safety.

Source:

Indian Express

Mains Practice Question:

Discuss the seismic vulnerability of Delhi in comparison to the Himalayan region. How do their geological features influence the frequency and intensity of earthquakes?