Maarg Manthan · Topic 3.3

Distribution of Earthquakes and Earthquake Observatories

Geography › Geomorphic Processes and Landform Evolution · Topic 3.3

Earthquakes are not scattered evenly but occur in narrow belts that follow plate boundaries. About 80 per cent occur in the circum-Pacific belt, about 15 per cent in the Alpine-Himalayan (Mediterranean-Asiatic) belt, and the rest along mid-oceanic ridges and in plate interiors. In India, the Himalayan arc, the Indo-Gangetic plain, the Kachchh region and the Andaman and Nicobar Islands are the most vulnerable. Earthquakes are recorded by global and national networks of observatories, such as the National Centre for Seismology in India.

6 min read · UPSC Prelims · Geography · Geomorphic Processes and Landform Evolution

At a Glance

Circum-Pacific belt About 80 per cent of earthquakes
Alpine-Himalayan belt About 15 per cent
Mid-oceanic ridges Shallow, smaller earthquakes
India Four seismic zones, II to V (2016 map)
Indian agency National Centre for Seismology
Exam link UPSC Prelims, Geography: Geomorphic Processes and Landform Evolution

Where Does It Fit?

This topic follows the one on locating epicentres and maps where earthquakes occur. It links the distribution to plate boundaries and then lists the observatories that record them, and it sets up the matching topic on volcanoes. Previous topic: Shadow Zone and Locating an Epicentre. Next topic: Volcanoes: Types (Shield, Composite, Caldera, Flood Basalt, Mid-Ocean Ridge).

Which Are the Three Main Belts?

Belt	Extent	Share and features
Circum-Pacific belt	Rim of the Pacific Ocean	About 81 per cent of the largest earthquakes; most volcanoes; subduction zones; deep earthquakes
Mediterranean-Himalayan (Alpine) belt	From the Mediterranean through Turkey, Iran, the Himalayas and Myanmar to Indonesia	About 15 to 17 per cent of earthquakes; collision zone with fewer volcanoes, except in the Mediterranean (Etna, Vesuvius, Stromboli) and Indonesia
Mid-oceanic ridge belt	Along the Mid-Atlantic, Indian and Pacific ridges	Frequent shallow, weaker earthquakes; mostly submarine volcanism; Iceland, Azores

Additional areas of activity are intraplate: the Hawaiian hotspot, the East African Rift and the Yellowstone region, described in Extrusive Volcanic Landforms: Geysers and Hot Springs and Plate Boundaries: Divergent, Convergent, Transform. Large earthquakes can also happen within old continental interiors, though rarely, as with the 1811-12 New Madrid earthquakes in the USA and the 2001 Bhuj earthquake in India’s Kachchh.

Why Do the Two Phenomena Coincide?

The distribution of earthquakes and of volcanoes follows the same pattern. Earthquakes and volcanoes occur together because both are driven by plate motion. At subduction zones the sinking plate causes earthquakes, as it grinds and bends, and also feeds magma to volcanoes above it. At divergent boundaries, rifting causes shallow earthquakes while magma rises. At transform boundaries there are earthquakes but few volcanoes, and in continental collisions there are strong earthquakes and few volcanoes. This overlap is why a map of earthquake epicentres and a map of volcanoes look almost identical, and why the line of epicentres outlines the plate boundaries, as in Plate Tectonics: Major and Minor Lithospheric Plates.

How Is the World Network of Observatories Organised?

Global Seismographic Network: a worldwide set of digital stations run by universities and the United States Geological Survey, which makes data open.
International Seismological Centre: in the United Kingdom, collects and publishes data from stations of many countries.
United States Geological Survey and the European-Mediterranean Seismological Centre: give rapid reports of large events.
Comprehensive Nuclear-Test-Ban Treaty Organization: runs an International Monitoring System with seismic stations, mainly to detect underground nuclear tests, and the data also record natural earthquakes.
India: the National Centre for Seismology under the Ministry of Earth Sciences, formerly part of the India Meteorological Department, runs the National Seismological Network of about 150 stations. It gives earthquake reports and alerts, and works with the Indian Tsunami Early Warning Centre. The Geological Survey of India and research institutes also study active faults.

The numbers of stations change as networks grow, so the latest figures should be checked on the official sites.

What Is the Situation in India?

India has just one confirmed active volcano, Barren Island in the Andaman Sea, and a dormant volcano, Narcondam Island. The Deccan Traps, Dhinodhar hills and other volcanic features are extinct. However, India has large seismic belts: the Himalayan arc from Jammu and Kashmir to the Northeast, the Indo-Gangetic plain, the Kachchh region of Gujarat and the Andaman and Nicobar Islands. The seismic zones of India are fixed by the Bureau of Indian Standards and are used for building codes. The 2016 code, IS 1893 (Part 1), has four zones, II to V, with Zone V the most severe and covering the Northeast, parts of Jammu and Kashmir, Himachal Pradesh, Uttarakhand, the Rann of Kachchh and the Andaman and Nicobar Islands.

A revised code issued in late 2025 introduced a sixth, higher-risk zone for the entire Himalayan arc, but the Bureau of Indian Standards withdrew it in March 2026, so the four-zone map of 2016 remains the one in force. As an analytical point, the withdrawal shows that seismic zoning involves a balance between hazard science and the cost of construction, and that students should always note the date of a map or code when quoting it.

What Are the Major Earthquake Disasters in India?

Kachchh (Bhuj), 2001: magnitude 7.7, killing about 20,000 people, in the interior of the plate.
Latur, 1993: a shallow earthquake in peninsular India, a stable region.
Kashmir, 2005: magnitude 7.6, in the Himalayan collision zone.
Sikkim, 2011: magnitude 6.9, in the eastern Himalaya.

Peninsular India was long thought to be stable, but the Latur and Bhuj events showed that it also has hazard, mostly from reactivated old faults. Earthquake causes are discussed in Earthquakes: Types, Causes, Effects and Frequency.

How Should the Distribution Be Remembered?

The pattern can be remembered by type of plate boundary. Convergent boundaries and subduction zones have the largest and deepest earthquakes, as around the Pacific, in the Himalaya and in the Mediterranean. Transform boundaries, such as the San Andreas Fault, have shallow, destructive earthquakes. Divergent boundaries, such as the mid-oceanic ridges and the East African Rift, have smaller, shallow ones. The plate boundaries are explained in Plate Boundaries: Divergent, Convergent, Transform. Plate-interior events, such as Latur in 1993 and Bhuj in 2001, are rarer and arise from old, reactivated faults. The causes and measurement of earthquakes are in Earthquakes: Types, Causes, Effects and Frequency. As an analytical point, the map of earthquakes is almost the same as the map of plate boundaries, and that is the best evidence for plate tectonics.

Why Is This Topic Important?

Map Belts are asked
India Zones and major quakes
Agencies Observatories

What Came Next?

The next topic begins the study of volcanoes and their types. Next topic: Volcanoes: Types (Shield, Composite, Caldera, Flood Basalt, Mid-Ocean Ridge).

Key People and Terms

Circum-Pacific belt Ring of earthquakes around the Pacific
Alpine-Himalayan belt Belt from the Mediterranean to Indonesia
Seismic zone Region of similar hazard
NCS National Centre for Seismology
BIS Bureau of Indian Standards
Intraplate earthquake Earthquake within a plate

Exam Corner

Points to Remember

About 80 per cent of earthquakes are in the Pacific belt.
The Alpine-Himalayan belt has about 15 per cent.
India has four zones (II to V) in force.
Bhuj earthquake: 2001, magnitude 7.7.
The NCS is under the Ministry of Earth Sciences.

Do Not Confuse With

Interplate and intraplate earthquakes At boundaries versus inside plates
Zone V and Zone II Highest hazard versus lowest in the current map
NCS and GSI Earthquake monitoring versus geological survey

Memory Hook

Pacific eighty, Alpine fifteen; the plate edges are where shakers are seen.

Mains Angle

Questions link earthquakes with plate tectonics and disaster management. These points add depth.

Pattern Follows plate boundaries
India Himalayan arc and Kachchh
Preparedness Zoning, codes and monitoring

A Question You May Face

An original practice question, not a past paper question.

“Describe the global distribution of earthquakes and discuss the vulnerability of India with reference to its seismic zones.”

How to Answer

Global Three belts.
Reason Plate boundaries.
India Zones and major events.
Response Codes and monitoring.

GS Relevance

Prelims: earthquake belts, Indian seismic zones, observatories and major Indian earthquakes. GS Paper 1: distribution of earthquakes; GS Paper 3: disaster management.

Frequently Asked Questions

Which are the main earthquake belts of the world?

The main earthquake belts are the Circum-Pacific belt, which has about 81 per cent of the largest earthquakes, the Mediterranean-Himalayan belt, with about 15 to 17 per cent, and the mid-oceanic ridge belt, which has frequent but weaker shallow earthquakes.

Why do volcanoes and earthquakes occur in the same areas?

Both are caused by the movement of tectonic plates. Subduction zones cause earthquakes as the plates grind, and also supply magma to volcanoes. As a result the maps of volcanoes and earthquake epicentres closely resemble each other and outline the plate boundaries.

How many seismic zones does India have?

India follows IS 1893 (Part 1) of 2016, which has four seismic zones, II to V, with Zone V the highest risk. A revised code of 2025 added a Zone VI for the Himalayan arc, but it was withdrawn in March 2026.

Which agency monitors earthquakes in India?

The National Centre for Seismology, under the Ministry of Earth Sciences, monitors earthquakes in India through its National Seismological Network of about 150 stations. It reports the time, location and magnitude of events, and works with agencies for tsunami warning, disaster response and research on active faults.

Where do most earthquakes occur in the world?

Most earthquakes, about 80 per cent, occur in the circum-Pacific belt, the Ring of Fire, where oceanic plates sink under continents. About 15 per cent occur in the Alpine-Himalayan belt, which stretches from the Mediterranean through Turkey, Iran and the Himalaya to Indonesia.

PYQ Practice — Statement Analysis

1 The Ring of Fire has about 90 per cent of the world's earthquakes.

True

It follows many subduction zones.

2 Barren Island in the Andaman Sea is an active volcano of India.

True

It is the only confirmed one.

3 Most volcanoes of the world lie in the interior of plates.

False

They lie along plate boundaries.

4 India's current seismic zonation has five zones, II to VI.