Context:.Recent earthquakes, in and around Delhi (12 since May, most powerful 3.4 magnitude) have triggered discussions on the possibility of increased seismicity around Delhi, and fears of an impending big earthquake sometime soon. None of these apprehensions have any scientific basis.
Is it unusual?
- Scientists are unequivocal in asserting that no unusual seismic activity is taking place around Delhi in the last few months.
- According to the earthquake catalogue, 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 sometimes you would expect to see a higher number of earthquakes as well.
- Detection of earthquakes, depends on the number of seismic recorders installed in that area. The area around Delhi has the most dense concentration of seismometers anywhere in the country, even more than the Himalayan region which is seismically much more active.
Do these small earthquakes foretell a bigger one?
- Earthquakes of magnitude four 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.
- And, they certainly do not signal any big upcoming event.
- The concept of foreshocks tells that when a big event happens, all the smaller earthquakes that have occurred in that region in the near past are classified as foreshocks.
So all this talk of these being foreshocks of a big earthquake in Delhi have no basis at all. However, a big earthquake might still occur, no one can rule it out. But they cannot be predicted.
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.
- Predicting earthquakes in a region like Delhi is all the more difficult because the place does not lie on any fault lines.
- Some special earthquakes, the ones that are triggered by volcanic activity, can be predicted to some extent.
Chances of a big earthquake coming to the 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.
- But 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.
- The argument that the smaller quakes are helping release the energy bit by bit so that a big one would not be necessary also does not hold.
- No one knows whether a big earthquake is going to hit Delhi or not, but a more relevant question is what even if we knew.
- Prediction is not going to make us safe against earthquakes.
- The need of the hour is
- To make our structures earthquake resistant,
- To follow prescribed drills when an event happens,
- Everyone must know what is the best place to run to when we are in the office, or at home, or in open spaces.
So a big earthquake is very much possible in Delhi. But they will come unannounced. Hence, pre and post-disaster preparedness is what is required.
- An earthquake is shaking or trembling of the earth’s surface, caused by the seismic waves or earthquake waves that are generated due to a sudden movement in the earth’s crust or upper mantle, due to the sudden release of energy.
- The instrument used to detect and record earthquakes is called a seismograph or seismometer.
Earthquake prone zones in India: