As Turkey and Syria deal with the aftermath of a deadly earthquake which hit the countries earlier this month and killed thousands of people, the answer to the question 'how prone is India to earthquakes?' is being sought.
According to the Ministry of Earth Sciences, approximately 59% of India's land mass is vulnerable to earthquakes of varying magnitude. Cities and towns in eight states and union territories are in seismic zone-5 and are vulnerable to the most powerful earthquakes. Even the National Capital Region is classified as zone-4, the second-highest level.
What are these seismic zones?
Beneath the Earth's surface, there are massive, irregularly shaped slabs of solid rock known as tectonic plates. These tectonic plates are always slowly moving, but they get stuck at their edges due to friction. When the stress on the edge overcomes the friction, there is an earthquake that releases energy in waves that travel through the earth's crust and is felt as the shake on the Earth's surface. These edges of the plates where the stress builds up are most prone to earthquakes and are known as seismic zones. The United States Geological Survey defines seismic zones as an area where earthquakes tend to focus.
In India, the National Centre for Seismology, which comes under the Ministry of Earth Sciences, is in charge of researching earthquake mechanisms and changes in seismic activity. It operates 115 observatories across the country and published a government report in 2021 that classified India into four seismic zones: zone five (the most dangerous), zone four, zone three, and zone two (least fatal).
Which parts of India come under these zones?
According to the report shared by the Ministry of Earth Sciences, approximately, "11% area of the country falls in zone V, 18% in zone IV, 30% in zone III and remaining in zone II".
Zone five includes parts of northeastern India, parts of Jammu and Kashmir, Himachal Pradesh, Uttaranchal, Rann of Kutch in Gujarat, part of North Bihar, and Andaman & Nicobar Islands. Zone four includes the remaining parts of Jammu & Kashmir and Himachal Pradesh, Union Territory of Delhi, Sikkim, northern parts of Uttar Pradesh, Bihar, and West Bengal, parts of Gujarat, and small portions of Maharashtra near the west coast and Rajasthan.
Zone three includes Kerala, Goa, Lakshadweep islands, remaining parts of Uttar Pradesh, Gujarat, and West Bengal, parts of Punjab, Rajasthan, Madhya Pradesh, Bihar, Jharkhand, Chhattisgarh, Maharashtra, Orissa, Andhra Pradesh, Tamil Nadu, and Karnataka. Zone two, the least seismic-prone zone, covers the remaining parts of the country.
Speaking to BOOM, V K Gahalaut, chief scientist at National Geophysical Research Institute, Hyderabad explained that the regions like Jammu and Kashmir, Assam, Andaman and Nicobar and Northern Bihar lie on the edges of the plates and hence are highly prone to earthquakes. "The regions lying in the rest of the three zones are closer to the center of the plates and hence not very vulnerable to high-intensity earthquakes," he said.
For instance, Assam, which lies in the easternmost projection of the Indian Plate, has had a history of natural disasters which include landslides, floods and earthquakes. The State experienced two major earthquakes in the years 1897 and 1950. The intensities of these two earthquakes were 8.7 and 8.5 on the Richter scales respectively. Gahalaut explained, "Assam is surrounded by many tectonic provinces – Eastern Himalayas to the north, Indo-Myanmar to the south-east and the Shillong Plateau to the south. Each of these tectonic provinces has numerous faults which makes it seismologically active and as a result, we get frequent earthquakes."
Similarly, Andaman and Nicobar islands are highly prone to earthquakes because of their geological location. Most earthquakes originate in the margins of the Great Nicobar Islands. The region is located in the Himalayan collision zone and is in the highest seismic-hazard zone. "The Andaman–Nicobar subduction system, which runs north-south, meets its onshore continuation, the Indo-Burmese arc, in the north. The Sumatra-Andaman and Indian subduction zones meet at the Indo-Burmese range, which is structurally complex and seismically active down to a depth of around 150 km," Gahalaut said, explaining the geology of the seismically active zone.
On December 26, 2004, an earthquake with a moment magnitude of 9.3 occurred along Northern Sumatra and the Nicobar and Andaman Islands which also resulted in a catastrophic tsunami.
Talking about the seismic activity in Kashmir, C P Rajendran, adjunct professor at the National Institute of Advanced Studies Bangalore, told BOOM, that the majority of Jammu and Kashmir is located in high seismic Zones IV and V which makes earthquakes a risk there. The geological past of this region suggests that it was formed when the Indian tectonic plate collided with the Eurasian plate. "As the tectonics is still actively shaping the topography and geology of the region, the occurrence of earthquakes in the area is potentially unavoidable," he said.
Exceptional cases: Delhi and Kutch
Though Delhi does not lie on the edge of a plate, it is still vulnerable to earthquakes. This is because it is not only affected by earthquakes in the Himalayan region but also has fault lines closer to it, Rajendran said. The Delhi-NCR region has several faults or weak zones that include the Delhi-Haridwar Ridge, Mahendragarh-Dehradun Subsurface Fault, Moradabad Fault, Sohna Fault, Great Boundary Fault, Delhi-Sargodha Ridge, Yamuna River Lineament, Ganga River Lineament and the Jahazpur Thrust.
Explaining the situation, Gahalaut said that the Delhi-Aravalli range was formed due to the collision of the Indian tectonic plate with the Eurasian plate and is older than the Himalayas. In the case of the Delhi-Aravalli range — also known as the Aravalli-Delhi Fold Belt — such tectonic movement in recent times may not give rise to new hills or mountains but may cause minor earthquakes.
Similarly, Kutch in Gujarat is not on the edge of a plate but still is a part of seismic zone five. Gahalaut said, "the region is highly complex because it is characterised by a number of East-West trending fault lines that act as seismic sources and periodically release continuously accumulating tectonic stresses that cause earthquakes". The main fault lines in the region include Kutch Mainland Fault (KMF), South Wagad Fault (SWF), Gedi Fault (GF), and Island Belt Fault (IBF) are seismically active. The region was devastated when a powerful earthquake of 7.7 magnitude hit Bhuj in 2001.
The domino effect
Based on the geology of a region, earthquakes may have other effects. For instance, Assam has seen many floods over the years. One major reason behind this could be the 1950 earthquake which jolted the region. Gahalaut explained the phenomena. "The earthquake and subsequent landslides, which followed over the years, led to a heavy deposition of sediments in the Brahmaputra river. As a result, the river bed rises and the width of the river increases, every time this happens," he said.
The Andaman and Nicobar Islands have also developed a heavily folded topography, over the years, in the aftermath of the earthquakes.
Infrastructure and earthquake
The Building Materials and Technology Promotion Council (BMTPC) is mandated to promote resource-efficient, climate-resilient, disaster-resistant construction practices including emerging building materials and construction technologies in India. It laid down guidelines for the construction of infrastructure in regard to Earthquake risk management and mitigation, in 2001. The guidelines have been revised over the years.
"The government has laid down the guidelines but they are not necessarily followed by the private constructors. The guidelines are mostly diluted by them to make up for exceeding construction costs," said Rajendran.
Speaking about the resilience of Indian infrastructures to earthquakes, Gahalaut said, "Infrastructures can never be strong enough in the face of massive earthquakes. However, we can reduce risks and damage if guidelines are followed properly".
Can we predict earthquakes?
Post the Turkey-Syria earthquake, there has been some scare-mongering predicting an even more devastating earthquake for India. Debunking the rumors, both experts said that while scientists have carried out research to identify regions that may be more prone to earthquakes, there is still no technology to predict their timings or magnitude.
Rajendran said, "Maybe in the coming years, with the help of satellites or other technology, we could predict their occurrence but as of now, this is not possible".