On Tuesday, a powerful 6.6-magnitude earthquake shook the Hindu Kush region of Afghanistan. There were significant tremors felt in Pakistan and northern India as well. The epicentre according to the United States Geological Survey, was in Afghanistan’s Jurm. It is not the first time that this kind of earthquakes has happed in India. In this article, we will try to find out the reason behind it.
Causes of Earthquakes in India
Earthquakes occur due to the movement of tectonic plates in the earth’s crust. When two blocks of the earth’s surface move against each other, it causes an earthquake. India experiences frequent earthquakes in the northern and northeastern regions because some parts of India and Nepal are located on the boundary (fault zones) of two massive tectonic plates. The Indian plate moved towards the Nepalese plate, which led to the formation of the Himalayas. The collision of the two plates also made both countries vulnerable to it.
Why Delhi-NCR is Facing Back-to-Back Earthquakes
Delhi and the National Capital Region are located on several active seismic fault lines, including the Sohna fault line, Mathura fault line, and Delhi-Moradabad fault line. Gurgaon is the most dangerous part of the region since it is situated on no less than seven fault lines. Delhi has always been prone to earthquakes since it is located in the fourth-highest seismic zone out of five classified by the Bureau of Indian Standards. While Delhi has never been the epicentre of any earthquake, it remains vulnerable to seismic activity.
Delhi’s development has been haphazard, characterized by dense construction of residential colonies and rampant illegal construction. Alarmingly, around two-thirds of the city’s population resides in illegally constructed buildings, raising serious concerns about their structural integrity. The collapse of a building in Laxmi Nagar a few years ago, without any seismic activity, has further exposed the poor quality of construction in the city. Moreover, the areas situated along the banks of the Yamuna river in Delhi are particularly susceptible to the highest level of danger.
Impacts of Earthquakes in India
Earthquakes can have severe impacts on people’s lives and property. While in India are generally of low to moderate intensity, they can still cause significant damage, particularly in densely populated areas. The recent earthquakes in Delhi and other northern states have led to panic among people, causing them to evacuate their homes and buildings. It can also lead to the collapse of buildings and infrastructure, resulting in loss of life and property damage.
The risk of earthquakes in India is categorized into four zones, namely Zone-2, Zone-3, Zone-4, and Zone-5, with Zone-2 being the least susceptible and Zone-5 being the most vulnerable. The states in the North-East, Jammu and Kashmir, Uttarakhand, and certain parts of Himachal Pradesh fall under Zone-5, whereas Delhi falls in Zone-4. Central India falls under the relatively safer Zone-3, while most of the southern region falls in the thicker classification of Zone-2 with limited danger.
However, it is important to note that there may be areas in Delhi that are as dangerous as Zone-5, and similarly, some parts of the southern states may pose a higher risk of earthquakes, similar to that of Zone-4 or Zone-5. Additionally, certain areas in Zone-5 may have a lower earthquake risk, making them less hazardous, just as some regions in Zone-2 may be more susceptible to earthquakes. Therefore, it is essential to thoroughly assess the earthquake risk of specific locations rather than relying solely on their zone classification
What is the Richter scale?
The Richter scale is a numerical gauge used to determine the strength of an earthquake. Specifically, it is known as the Richter Magnitude Test Scale, which measures the intensity of seismic waves produced during an earthquake. The scale is relatively small, ranging from one to nine, but it is important to note that there is no upper limit to its measurement, and it is possible for a quake to exceed nine on the scale, although no such occurrence has been recorded to date.
The Richter scale was developed in 1935 by Charles Richter, a scientist who worked alongside Beno Gutenberg at the California Institute of Technology.
Which kind of buildings is safe?
It is commonly believed that buildings erected on pillars are inherently safe during earthquakes. However, it should be noted that merely constructing a building on pillars only offers around 90-95 percent earthquake resistance. In New Zealand, experts are adopting base isolation techniques to retrofit old buildings and make them more earthquake-resistant. This method involves installing a flexible mantle structure around the building’s foundation, which restricts the earthquake’s vibrations to the lower portion of the structure.
According to Chandan Ghosh, a professor at IIT Jammu, buildings not constructed on pillars are at the greatest risk during earthquakes. In contrast, buildings with pillars vibrate simultaneously during seismic activity, whereas those without pillars have individual walls that move separately, causing the entire structure to collapse. Retrofitting such buildings by attaching them to pillars can significantly improve their stability and prevent individual walls from moving independently.
How to construct a house that is earthquake-proof
Constructing an earthquake-proof house involves several critical factors. Retrofitting is a recognized technique that is approved by the Bureau of Indian Standards, and any qualified civil engineer can employ this approach to retrofit an existing building. For buildings that are not constructed on pillars, a retrofitting method involves installing flexible lantern bands above the doors and windows at the roof level. Additionally, the corners of the building’s four walls are joined together using robust iron rods as reinforcement.
According to Professor Vasant Matsagar at IIT-Delhi, retrofitting is a superior method of earthquake-proofing, but it is crucial to retrofit older buildings as well. In Bhuj, various measures have been taken to retrofit older buildings, demonstrating that retrofitting is an effective approach to improve building safety in earthquake-prone areas.