World’s Major Earthquake Zones: Understanding the Causes and India’s Seismic Areas

Thousands of earthquakes occur on Earth each year. Some of them are powerful enough to alter the earth and cause damage to buildings, but the majority are so small that we can't even feel them. These seismic events typically occur in specific regions when the Earth's surface shifts and moves. They don't happen at random. Governments can create safer and more robust infrastructure, and scientists can alert the public about potential threats. 

Table of Contents:

• What Causes Earthquakes?
• The World's Major Seismic Zones
• Seismic Zones of India
• Why Is Northeastern India So Vulnerable?
• Earthquake Preparedness in India

What Causes Earthquakes?

Tectonic plates are the huge slabs that make up the outer shell of the Earth. These plates move slowly and continuously. When plates collide, pull apart, or slide past each other, stress builds up along fault lines. When that stress is suddenly released, it sends seismic waves through the earth, an earthquake. The point underground where the earthquake starts is called the focus or hypocenter, and the point on the surface directly above it is the epicentre.

The World's Major Seismic Zones

1. The Pacific Ring of Fire

The Ring of Fire is the most active earthquake area on Earth. It forms a curved, horseshoe-like path around the Pacific Ocean and stretches for about 40,000 kilometres. It passes through places like Alaska, Japan, the Philippines, Indonesia, New Zealand, and the western coasts of North and South America. Approximately 90% of all earthquakes and 80% of the largest earthquakes in the world occur in this area. Parts of the Earth's surface are continuously pushing and sliding beneath one another, causing regular shaking, which is why this location is so active.

2. The Alpide Belt

The Alpide Belt, which stretches from the Atlantic through the Mediterranean Sea, Iran, India, and Southeast Asia, is the second most seismically active region. It accounts for roughly 17% of the world's largest earthquakes. Countries such as Turkey, Iran, Pakistan, and parts of northern India lie within this belt. The catastrophic 2023 Turkey-Syria earthquake occurred along this zone.

3. Mid-Atlantic Ridge

The Mid-Atlantic Ridge runs along the middle of the Atlantic Ocean. It is a place where parts of the Earth slowly move away from each other. This area is important because earthquakes do happen here, and it also causes volcanic activity in places like Iceland. However, the earthquakes in this region are usually not as strong as those in other, more active areas.

4. East African Rift Zone

This area stretches from the Afar Triangle through countries like Kenya, Tanzania, and Mozambique. Here, the African land is slowly pulling apart over time. Earthquakes here are moderate but frequent, and the region experiences significant volcanic activity.

Seismic Zones of India

India is a seismically active country due to the northward drift of the Indian plate, which continues to collide with the Eurasian plate, the same geological force that built the Himalayas. Based on the degree of anticipated earthquake damage, the Bureau of Indian Standards (BIS) has classified India into four seismic zones:

India's Four Seismic Zones at a Glance

Zone II (Least Severe) - MSK Intensity VI or less

Includes portions of Tamil Nadu, Andhra Pradesh, Karnataka, Odisha, and eastern Rajasthan in addition to the majority of peninsular India. The ancient, comparatively stable Deccan Plateau is the location of this area. Earthquakes are infrequent and low-intensity, though not impossible - the 1993 Killari (Latur) earthquake in Maharashtra was a deadly reminder.

Zone III (Moderate) - MSK Intensity VII

Comprises the Andaman and Nicobar Islands, Kerala, Goa, central Maharashtra, portions of Uttar Pradesh, Punjab, and West Bengal. This area has a moderate risk, necessitating basic earthquake-resistant architecture. 

Zone IV (High) - MSK Intensity VIII

Comprises parts of Gujarat, Himachal Pradesh, Uttarakhand, Bihar, Ladakh (apart from the far north), Jammu & Kashmir, and the Delhi-NCR region. The disastrous Bhuj earthquake in Gujarat in 2001 had an impact on this region, highlighting the importance of earthquake preparedness. 

Zone V (Most Severe) - MSK Intensity IX and above

The Rann of Kutch, Jammu & Kashmir (the northern regions close to the Indus-Tsangpo Suture Zone), and all of northeastern India (Assam, Manipur, Meghalaya, Mizoram, Nagaland, Arunachal Pradesh, Sikkim) comprise the highest-risk area. Among the strongest earthquakes in Indian history are the 1950 Assam earthquake (magnitude 8.6) and the 1934 Bihar-Nepal earthquake (magnitude 8.1).

Why Is Northeastern India So Vulnerable?

The major tectonics of the Shillong Plateau, the subduction along the Burma Plate to the east, and the collision of the Indian and Eurasian plates to the north are the three main tectonic interactions that intersect the northeastern region. It is therefore among the continental areas on Earth with the highest seismic activity. 

Earthquake Preparedness in India

• Guidelines for earthquake-resistant buildings are established by the National Disaster Management Authority (NDMA).
• Each zone's structural safety requirements are outlined in the IS 1893 code. 
• Early warning systems and community drills are being expanded, especially in Zone IV and V cities.