Earthquakes in Kolka

Kolkata, the cultural capital of India, is known for its rich heritage, architectural beauty, and vibrant urban life. Unlike cities located directly along earthquake-prone fault lines, Kolkata is not usually considered a high-seismic zone. However, in recent decades, the city has experienced several mild to moderate tremors caused by regional seismic activity. Scientists warn that the city remains vulnerable due to its geographical location, soil characteristics, population density, and aging infrastructure. Understanding Kolkata’s earthquake risk is essential to strengthen safety measures and reduce future damage.

Earthquakes in Kolkata: Risks, History, and Preparedness

1. Geographical Setting and Seismic Background

Kolkata lies in eastern India, close to the boundaries of several major seismic zones. The city itself falls under Seismic Zone III, which represents moderate earthquake risk. Although this is not as dangerous as Zones IV or V, it still poses significant hazards due to the following reasons: a. Proximity to Active Seismic Regions Kolkata is influenced by seismic activity from: The Himalayan belt, one of the most active tectonic zones in the world The Shillong plateau, known for generating powerful quakes The Gangetic basin, with soft alluvial soil that amplifies tremors The Sundarbans region, where tectonic shifts occasionally cause mild tremors Major earthquakes in Nepal, Bhutan, Assam, or even Bangladesh can send shockwaves all the way to Kolkata. b. The Soft Soil Problem Kolkata is built on deep layers of alluvial deposits—soft soil that behaves like jelly during a quake. This type of soil: Amplifies seismic waves, making tremors feel stronger Increases the risk of liquefaction, where soil behaves like liquid Causes buildings to sway more intensely As a result, even a moderate earthquake can produce noticeable shaking in the city.

2. Historical Earthquakes Affecting Kolkata

Although Kolkata has not experienced a large, direct earthquake in recent history, several major quakes in the region have significantly impacted the city. a. The Great Bengal Earthquake of 1897 One of the most severe earthquakes in the region’s history, the Shillong Plateau quake (Magnitude 8.1), shook Kolkata violently. Buildings, chimneys, and bridges developed cracks, and the city's infrastructure sustained serious damage. b. The Bihar–Nepal Earthquake of 1934 This massive Magnitude 8.0 earthquake affected Kolkata even though its epicenter was far away. Many old buildings, including colonial structures, were damaged. c. The 1950 Assam Earthquake A Magnitude 8.6 quake—one of the largest worldwide—caused intense tremors in Kolkata. People rushed out of homes and offices as structures shook for several seconds. d. Recent Earthquakes Felt in Kolkata In the last decade, strong earthquakes in Nepal (2015), Myanmar (2016), Assam (2021), and the Bay of Bengal have caused noticeable tremors in Kolkata. These quakes: Lasted several seconds Caused mild panic Led to evacuation of high-rise buildings Produced cracks in a few old structures These repeated experiences remind residents of the city's vulnerability.

3. Why Kolkata Is at Risk Even Without a Local Fault Line

Kolkata is often mistaken as a low-risk city because no major fault lies directly under it. However, scientists have identified several hidden dangers. a. Outdated and Weak Buildings Many structures in Kolkata—especially old buildings in north and central parts—are: 70 to 150 years old Built without earthquake-resistant design Made of brittle brick masonry These buildings are more likely to collapse or crack during a strong tremor. b. Rapid Urbanization New neighborhoods with: High-rise buildings Narrow lanes Congested residential areas often lack proper disaster planning. c. Underground Infrastructure Kolkata has: Deep metro tunnels Old sewage systems Water pipelines High-rise foundations Earthquakes can cause underground shifts, leading to flooding, road collapse, or pipe bursts. d. Population Density With nearly 15 million people in the metropolitan area, even a moderate quake can cause: Panic Stampedes Injuries Disruption of essential services

4. Potential Impact of a Large Earthquake

Although no major quake has struck Kolkata directly in modern times, scientists warn that a strong regional earthquake could cause widespread damage. a. Building Collapse Older buildings, particularly in north Kolkata’s heritage zones, are highly vulnerable. Poorly maintained structures can collapse even during moderate seismic activity. b. Damage to Transportation Systems Earthquakes may disrupt: Metro services Flyovers and bridges Tramlines Ferries and jetties Airport operations Even temporary disruption can paralyze the city. c. Flooding Risk Liquefaction or pipeline damage can lead to: Sudden waterlogging Burst water lines Contamination of drinking water Kolkata, already a low-lying city, becomes more vulnerable. d. Economic Loss The city is an economic hub. Earthquakes can impact: IT parks Industries Banking and finance centers Tourism Large-scale tremors can result in billions of rupees in damage.

5. Preparedness and Safety Measures

To minimize risk, Kolkata must strengthen earthquake preparedness at multiple levels. a. Government Initiatives Introducing strict earthquake-resistant building codes Retrofitting old bridges, flyovers, and essential buildings Regular structural auditing of vulnerable buildings Training police, NDRF, and civic staff for emergency response Expanding early-warning systems b. Public Awareness Residents should be educated on: Safe evacuation methods Identifying weak building structures Emergency kits with water, first aid, torch, and documents Avoiding elevators during quakes Schools and offices must conduct mock drills regularly. c. Infrastructure Improvements Strengthening high-rise foundations Upgrading underground pipelines Designing quake-resistant metro corridors Ensuring open spaces for evacuation d. Technology and Monitoring Installing more: Seismic sensors GPS-based monitoring Automated warning systems can provide essential seconds of advance notice.

6. What To Do During an Earthquake
If Indoors

Drop, Cover, and Hold Stay away from windows and glass Take shelter under sturdy furniture Avoid stairs and elevators If Outdoors Move to open ground Stay away from trees, electric poles, and buildings If In a Vehicle Stop safely Do not park under bridges or flyovers Conclusion Kolkata may not lie directly on a major fault line, but its soft soil, aging buildings, and proximity to active seismic zones make it vulnerable to earthquake damage. Past experiences show that even distant earthquakes can create strong tremors in the city. Preparing Kolkata for potential seismic events is not just a scientific necessity but a crucial step toward protecting millions of lives.