Headline : Why are quakes happening at Palghar?
- Maharashtra’s Palghar district has been hit by a series of low-intensity earthquakes since November last year.
- The National Centre for Seismology (NCS) has categorised these unusual tremors as an ‘earthquake swarm’.
What is Earthquake swarm?
- In ‘earthquake swarms’, numerous earthquakes occur locally over an extended period without a clear sequence of foreshocks, main quakes and aftershocks.
- When seismic energy piles up inside the Earth and is released in small amounts from certain points, such a series of earthquakes can occur.
- The development of an earthquake swarm over time is just as difficult to predict as earthquakes are in general.
- Many earthquake swarms occur in regions with complex contiguous fracture systems.
- The theory is that they are related to the movement of fluid gases and liquids in the Earth’s crust.
Note: If earthquake swarm is followed by a big earthquake, then it is considered as a foreshock.
- Palghar has been witnessing an unusual frequency of earthquakes since November, 2018.
- Researchers have concluded that the swarms were related to the monsoon, and were attributable to a phenomenon called “hydro-seismicity.”
- Hydro-seismicity: When water from heavy rainfall enters small fractures in rocks, this raises the pressure. This pressure is released in earthquake swarms.
- In 2007, a study by researchers from IIT-Bombay suggested that swarm activity along the west coast was due to a major fault parallel to it. However, more evidence is needed to determine the extent of this fault and how active it is.
- In general, earthquakes are caused by geological faults, or cracks in the earth’s crust across which rocks get displaced and there are plenty of faults along the Konkan coast of India (where Palghar lies), although how many of these are active isn’t known.
- Thus, It is still not clear whether these earthquakes are swarms only or a series of foreshocks before a major earthquake.
- In areas of high seismicity, buildings construction should be based upon Bureau of Indian Standards (BIS) codes, which are likely to survive swarms and even larger quakes. So, it is crucial for the code to be implemented stringently.