According to the data compiled by USA’s National Oceanic Atmospheric Administration, the frequency of earthquakes around the world is increasing every year. However, the data also indicates that the frequency of high-intensity earthquakes is decreasing frequently. Over the years there has been advancement in both earthquake detection technology and earthquake-resistant technology, especially in places such as Japan where high-intensity earthquakes are frequent.
India is generally considered a stable region. A significant portion of India, especially the Deccan plateau is in the low-risk zone. In India, earthquakes are more common around tectonic plate boundaries and the western coastal regions. In the last few years, natives of the Delhi-NCR region experienced frequent earthquakes, some even occurring in the span of a week. Now, why do earthquakes occur in the first place? And why has their frequency increased in the last couple of years?
Why do earthquakes occur?
There are several different causes of earthquakes. Let’s break them down one by one.
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Tectonic earthquakes- Earthquakes caused by the movement of tectonic plates are known as tectonic earthquakes. They commonly occur worldwide at the boundary of the tectonic plates. When the tectonic plates of the Earth’s crust and the upper mantle collide, they lock when they move past one another building pressure which when released causes earthquakes.
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Volcanic earthquakes- As the name suggests, volcanic earthquakes are caused when a volcano erupts releasing a large amount of embedded pressure which then generates seismic waves that cause the earth to shake. Volcanic earthquakes are neither as common nor as strong as tectonic earthquakes.
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Man-made earthquakes- Man-made earthquakes or induced earthquakes are earthquakes caused by mining and extraction of natural resources-related disasters. Induced earthquakes are also caused by creating artificial lakes and the overfilling of dams.
Seismic Zoning of India
The Geological Survey of India has published a seismic zoning map of the country which is based on the amount of damage suffered by the different regions of India because of earthquakes. The impact of earthquakes in each zone is calculated using the Modified Mercalli scale. This map is used by the Department of Disaster Management as it helps them prepare and plan for earthquakes. The following are the seismic zones of the nation-
Zone II- Zone II is the least active seismic zone. Parts of eastern Punjab and Haryana, the western part of Rajasthan, the northern half of Madhya Pradesh, the southern part of Uttar Pradesh, Chhattisgarh, Odisha, Telangana, Andhra Pradesh, Karnataka, and Tamil Nadu are included in Zone II.
Zone III- Zone III experiences mild to moderate seismic action. Zone III includes the state of Kerala, Goa, the coast of Andhra Pradesh, Karnataka, Maharashtra, Gujrat, and West Bengal, the central part of Uttar Pradesh, the northern half of Jharkhand, and the rest of the states of Haryana, and Punjab
Zone IV- Zone IV is considered the zone which experiences high seismic action. Zone IV includes parts of Maharashtra, Gujrat, West Bengal, Bihar, Uttar Pradesh, New Delhi, Uttarakhand, Himachal Pradesh, Sikkim, Ladakh, Jammu and Kashmir, and the northernmost part of Punjab and Haryana.
Zone V- Zone V is the zone with the highest seismic activity. Gujrat, Jammu & Kashmir, Himachal Pradesh, Uttarakhand, Bihar, Meghalaya, Assam, Manipur, Arunachal Pradesh, Nagaland, Tripura, and Mizoram are a part of Zone V.
Why is India Prone to Earthquakes?
The National Disaster Management Authority of India says that “India’s increasing population and extensive unscientific constructions mushrooming all over, including multi-storied luxury apartments, huge factory buildings, gigantic malls, supermarkets as well as warehouses and masonry buildings keep-India at high earthquake risk.”
It adds, “The increase in earthquake risk is due to a spurt in developmental activities driven by urbanization, economic development, and the globalization of India’s economy. The increase in the use of high-technology equipment and tools in manufacturing and service industries has also made them susceptible to disruption due to relatively moderate ground shaking.”
Other than just man-made earthquakes, India is also prone to high frequency and intensity of earthquakes because the Indian tectonic plate is moving towards the Eurasian tectonic plate at a rate of approximately 50 mm/year. India experiences the most severe tectonic earthquakes around the Himalayan belt.
The Himalayan belt is the place of a lot of tectonic activities because the Indo-Austral plate collides with the Eurasian and Burma plate there. Dr. Sandip Som, the deputy general of the Geological Survey of India says that “Main strain and stress build-up areas have been noted along the convergence zone between Indian and Eurasian plates. Due to continuous plate movement, stresses build up in this area. Moreover, there are around 30 water reservoirs along the WGE (Western Ghat Escarpment). Enhanced water load in the reservoirs increases pore pressure and stress, triggering earthquakes,”
The Geological Survey of India has deployed 30 permanent GPS stations to monitor tectonic plate movement and identify potential hazardous zones. The coastal area of India is the next most prone part of India. Earthquakes caused in the coastal region take place because of seafloor displacement and underwater volcanic activities. Delhi and the general NCR region experience frequent earthquakes because Delhi is located on three active seismic fault lines: the Sohna fault line, the Delhi-Moradabad fault line, and the Mathura fault line.
In India, the earthquakes experienced in the last few years, which were of small magnitudes, have mainly occurred due to foreshocks and swarms. According to the Geological Survey of India, the series of earthquakes or mild tremors preceding earthquakes indicate the release of tectonic stress and strain caused during the continuous deformation process. Many studies show that these activities can also predict the eventuality of a significant seismic event.
List of Major Earthquakes in India
Although seismic activity is frequent in India, it is generally not of high intensity. However, in the past, there have been several earthquakes that have caused large-scale devastation.
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The Indian Ocean (2004)- The biggest earthquake to date occurred in 2004 in the Indian ocean. The death toll exceeded 280,000.
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Kashmir (2005)- With a magnitude of 7.6, the epicenter of this earthquake was Muzaffarabad, Kashmir (Pakistan). Approximately 130,000 lost their lives.
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Bihar (1934)- The epicenter of this earthquake was the southernmost part of Mount Everest. Tremors of magnitude 8.7 were felt across Bihar and Nepal and led to the death of 30,000 people.
