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An Earthquake of 6.4 magnitude hit Assam on April 28th, 2021. It caused sufficient damage to buildings and property but fortunately, no fatalities were reported. The northeastern region has a peculiar record of experiencing earthquakes at regular intervals due to its unique geographical location. The state of Assam itself witnessed two great earthquakes (Magnitude >8) in 1897 and 1950.
In this article, we will try to ascertain the reasons behind the occurrence of earthquakes, their brutal impacts, and the vulnerability of the northeast region that converts it into a disaster. Further, we will try to find out what rational measures should be taken for developing robust earthquake resilience.
How does an earthquake occur?
- Firstly, an earthquake occurs when there is a sudden release of energy in the Earth’s lithosphere that creates seismic waves.
- Secondly, the release of energy occurs along a fault. A fault is a sharp break in the crustal rocks.
- Thirdly, rocks along a fault tend to move in opposite directions. As the overlying rock strata press them, the friction locks them together. However, their tendency to move apart at some point in time overcomes the friction.
- Fourthly, as a result, the blocks get deformed, and eventually, they slide past one another abruptly. This causes a release of energy, and the energy waves travel in all directions.
Read More – Basics of Earthquake
- Focus: The point where the energy is released is called the focus of an earthquake. It is also called the hypocentre.
- Epicentre: The energy waves travelling in different directions reach the surface. The point on the surface, nearest to the focus, is called the epicentre.
- Recently an earthquake of magnitude 6.4 on the Richter scale hit Assam. It occurred near Dhekiajuli in the Sonitpur district of Assam, 80 kilometres northeast of Guwahati.
- Following the main tremors, six aftershocks (of magnitude ranging from 3.2 to 4.7) also occurred within two-and-a-half hours.
- The National Centre for Seismology (NCS) recently mentioned that these tremors were attributed to the Kopili Fault Zone.
About Kopili Fault Zone
- It is a 300-km northwest-southeast trending fault. It extends from the western part of Manipur to the tri-junction of Bhutan, Arunachal Pradesh, and Assam.
- The zone has witnessed many seismic activities in the past. This includes the 1869 earthquake (7.8 magnitude) and the 1943 earthquake (7.3 magnitude).
- The zone is located closer to Himalayan Frontal Thrust (HFT).
- It is a geological fault along the boundary of the Indian and Eurasian tectonic plates.
History of Earthquakes in the Northeast Region
- The North-Eastern part of the country continues to experience moderate to large earthquakes at frequent intervals. This includes the two great earthquakes -1897 Shillong (Magnitude – 8.7) and 1950 Assam-Tibet (Magnitude – 8.6).
- On average, the region experiences an earthquake with a magnitude greater than 6.0 every year.
Vulnerability of Northeast Region to Earthquake
- High Seismicity Level: Northeast is located in the highest seismological zone. The Kopili Fault Zone is a seismically active area, so it falls into the highest Seismic Hazard Zone V. It is associated with collisional tectonics because the Indian Plate is subducting beneath the Eurasian Plate.
- Nature of Soil: Kopili fault zone and its neighbouring areas are characterized by alluvial soils. These alluvial soil have a higher potential of trapping seismic waves. Thus making the region the most earthquake-prone zone in North East India.
- Terrain: The region has a significant amount of mountainous terrain that demands explosions for building a tunnel, road, etc. infrastructure. This enhances the probability of earthquakes.
- Untapped Potential: The region has not seen robust development like the rest of India. Thus, a greater number of development projects like mining, dam construction, etc. in the region are under planning. It may enhance earthquake probability in the future.
- High-technology equipment and tools: There has been an increase in the use of high-technology equipment and tools in the manufacturing and service industries. This has made them susceptible to disruption even by moderate ground shaking.
- Unscientific Buildings: Many buildings in the cities of Shillong, Gangtok etc. are constructed on the sloping ground. That too by excavating some part of the hill.
- The open ground storey, heavy overhangs, heavy rooftops, and irregular plan shapes are common in buildings that make them seismically more vulnerable.
- Policy gap: There is a considerable knowledge and policy gap regarding earthquakes in the Northeast. Even a good knowledge about the Kopili fault did not result in disaster reduction policies.
Earthquake Zonation in India
- India has been divided into four seismic zones (II, III, IV, and V) based on scientific inputs relating to seismicity, earthquakes that occurred in the past and the tectonic setup of the region.
Source: National Institute of Disaster Management
General reasons behind the occurrence of earthquakes
- Firstly, Tectonic Activities: Sliding of rocks along a fault plane can cause sudden shaking of the ground, resulting in an earthquake.
- Secondly, Volcanic activities: A special class of tectonic earthquakes is sometimes recognized as a volcanic earthquake. However, these are confined to areas of active volcanoes.
- Thirdly, Human-Induced: Minor earthquakes and tremors that are caused by human activity like mining, large-scale petroleum extraction, artificial lakes (reservoirs), nuclear tests, etc.
- Collapse Earthquakes: In the areas of intense mining activity, sometimes the roofs of underground mines collapse causing minor tremors.
- Explosion Earthquakes: Ground shaking may also occur due to the explosion of chemical or nuclear devices. Such tremors are called explosion earthquakes.
- Reservoir-induced: The earthquakes that occur in the areas of large reservoirs are referred to as reservoir-induced earthquakes.
Impact of Earthquake
- Loss of Human Lives: The earthquakes have eaten up thousands of precious human lives across the world.
- Around 1,542 deaths occurred in Assam during the 1897 Great Earthquake.
- Infrastructural Damage: Several houses and buildings were damaged after an earthquake of magnitude 6.4 hit Assam.
- Similarly, the great Assam earthquake (1897) reduced all masonry buildings to debris within a region of northeastern India. This is roughly the size of England.
- Initiating another disaster: The 1950 Assam earthquake caused huge landslides. These landslides in turn blocked many rivers in the mountainous region and caused floods.
- Land Degradation: The recent Kolipi Fault zone earthquake caused cracks in a paddy field situated in Tatkal Basti village of Misamari, a town on the Assam-Arunachal Pradesh foothills.
- Economic Losses: A significant amount is spent on reconstructing the lost infrastructure, rehabilitation of masses, and providing relief support to the impacted people.
- Firstly, the government has to fix the knowledge and policy gap regarding earthquakes in North East India.
- Secondly, the government has to build an effective Earthquake mitigation plan. This would involve constructing resilient infrastructure among other things.
- For instance, the Delhi Metro pillar can easily withstand an earthquake of magnitude 9.
- Thirdly, an integrated disaster management plan should be developed for the North East. This plan will help in tackling these types of high-intensity earthquakes.
- Fourthly, due adherence to Environmental impact assessment must be observed before initiating mining or dam construction.
- Fifthly, more funding should be given to Earthquake planning and mitigating agencies to improve disaster management potential.
- For instance, the National Centre for Seismology has developed ‘India Quake’. An App for Earthquake Parameter Dissemination
Being in the seismic zone 5, earthquakes are bound to occur in the northeast region. The government is incapable of stopping their occurrence. Although it can definitely curtail their adverse impact by developing robust resilience in consonance with Sendai Framework for Disaster Risk Reduction 2015-2030.