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Delhi Earthquakes

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June 09, 2020

What is the issue?

  • An earthquake of magnitude 2.1 was detected near Delhi on June 08, 2020.
  • This is the eleventh minor earthquake that is being recorded in and around Delhi since May.

What are the discussions?

  • These recent earthquakes have triggered discussions on the possibility of increased seismicity around Delhi.
  • They have also triggered fears of an impending big earthquake soon.
  • None of these apprehensions has any scientific basis.

Is it unusual for Delhi to experience so many earthquakes?

  • Nothing unusual - Scientists assert that no unusual seismic activity is taking place around Delhi in the last few months.
  • Delhi and its surrounding areas usually experience between two and three earthquakes of magnitude 2.5 and above every month.
  • But there are monthly and annual variations as well.
  • Geological and seismological processes are not very smooth.
  • So nothing special has happened in Delhi in the last couple of months.
  • Detection - Detection of earthquakes, especially those of smaller magnitude, being recorded in an area also depends on the number of seismic recorders installed in that area.
  • The area around Delhi has the densest concentration of seismometers in the country, even more than the seismically active Himalayan region.
  • Out of the 115 detectors installed in India, 16 are in or around Delhi.
  • As a result, even the earthquakes of smaller magnitude are recorded, and this information is publicly accessible.

Do these small earthquakes foretell a bigger one?

  • Scientifically - Earthquakes of magnitude 4 or below hardly cause any damage anywhere and are mostly inconsequential for practical purposes.
  • Thousands of such earthquakes are recorded around the world every year, and most of them are uneventful.
  • They certainly do not signal any big upcoming event.
  • Foreshocks -Foreshocks are post-event definitions, which is something that is largely applied in hindsight.
  • When a big event happens, all the smaller earthquakes that have occurred in that region in the near past are classified as foreshocks.
  • The description does not exist before any big earthquake has happened.
  • So, the talk of these being foreshocks of a big earthquake in Delhi have no basis at all.
  • Reality - A big earthquake might still occur, which no can rule out. But they cannot be predicted.
  • So to say that these small earthquakes are precursors to the big one is totally unscientific.

What is a signal to an upcoming earthquake?

  • Scientists have been working for years to identify “precursors” to an earthquake, but have so far met with no success.
  • Some special earthquakes, triggered by volcanic activity, can be predicted to some extent but nothing else.
  • Predicting earthquakes in a region like Delhi is all the more difficult because the place does not lie on any fault lines.
  • We know a little bit about the tectonics in the Himalayan region, where two tectonic plates are meeting each other.
  • But Delhi is located on a single plate, and the seismic activity is generated by internal deformities.
  • Therefore, predicting earthquakes in advance is out of the question.

Is a big earthquake coming to the Himalayan region?

  • Scientists say that the Himalayan region is due for a big earthquake, of magnitude 8 or even higher.
  • That is because they have been able to measure the energy that is getting trapped under the surface as a result of one tectonic plate trying to move beneath the other one.
  • Even here, scientists have no idea when this big earthquake will occur.
  • The prediction about the big one is based only on the estimate of the energy that is ready to be released.
  • An earthquake of magnitude 6 is typically associated with the kind of energy that was released by the atom bomb in Hiroshima.
  • An earthquake of magnitude 8 would be almost 1,000 times more powerful than a magnitude 6 event.
  • Even the argument that the smaller quakes are helping release the energy bit by bit so that a big one would not be necessary does not hold.
  • 1,000 earthquakes of magnitude 4 are needed to release the energy equivalent of a magnitude 6 earthquake. These arguments have no basis.

Is a big earthquake coming to Delhi?

  • No one knows, but a more relevant question is what even if we knew.
  • Prediction is not going to make us safe against earthquakes.
  • It is important that we need to make our structures earthquake resistant, we need to follow prescribed drills when an event happens.
  • These kinds of discussions are the meaningful ones.
  • No one is ruling out a possibility of a big earthquake in Delhi.
  • But they would occur when they have to.

 

Source: The Indian Express

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