For NDA & CDS 2 2026 aspirants, Plate Tectonics and Earthquakes are among the most important topics in Physical Geography. Questions are frequently asked about the Earth’s structure, tectonic plates, seismic waves, earthquake zones, and volcanic activity. A strong understanding of these concepts helps candidates tackle both static GK and geography-based current affairs questions.
NDA & CDS 2 2026 Exam GK – Geography – Plate Tectonics & Earthquake
The Earth’s surface is not a single solid piece but is divided into several large and small plates that are constantly moving. The scientific theory explaining these movements is known as the Theory of Plate Tectonics. The movement of these plates causes earthquakes, volcanic eruptions, mountain building, and the formation of ocean basins.
Understanding plate tectonics is essential for studying the dynamic nature of the Earth and the occurrence of natural disasters such as earthquakes and tsunamis.
Interior Structure of the Earth
The Earth consists of three major layers:
1. Crust
- The outermost solid layer.
- Thickness varies from about 5 km beneath oceans to 70 km beneath continents.
- Continental crust is mainly composed of silica and aluminium (SIAL).
- Oceanic crust is rich in silica and magnesium (SIMA).
2. Mantle
- Extends up to about 2,900 km below the surface.
- Composed of dense silicate rocks.
- Contains the semi-molten Asthenosphere on which tectonic plates move.
3. Core
- Divided into Outer Core and Inner Core.
- Outer core is liquid and mainly composed of iron and nickel.
- Inner core is solid due to immense pressure.
- Responsible for Earth’s magnetic field.
Theory of Plate Tectonics
The Plate Tectonic Theory was developed in the 1960s and explains that the Earth’s lithosphere is broken into several rigid plates that float over the semi-fluid asthenosphere.
Major Tectonic Plates
- Pacific Plate
- Eurasian Plate
- North American Plate
- South American Plate
- African Plate
- Antarctic Plate
- Indo-Australian Plate
Minor Plates
- Arabian Plate
- Caribbean Plate
- Nazca Plate
- Philippine Plate
- Cocos Plate
- Scotia Plate
The Indian Plate, a part of the Indo-Australian Plate, is moving northward and colliding with the Eurasian Plate, resulting in the formation of the Himalayas.
Types of Plate Boundaries
1. Divergent Boundary
- Plates move away from each other.
- New crust is formed.
- Associated with mid-ocean ridges.
Examples:
- Mid-Atlantic Ridge
- East African Rift Valley
2. Convergent Boundary
- Plates move towards each other.
- One plate may subduct beneath another.
- Causes mountain formation, volcanoes, and powerful earthquakes.
Examples:
- Himalayas
- Andes Mountains
3. Transform Boundary
- Plates slide past each other horizontally.
- Produces frequent earthquakes.
Example:
- San Andreas Fault (California)
Continental Drift Theory
Proposed by German scientist Alfred Wegener in 1912.
Main Idea
- All continents were once joined into a supercontinent called Pangaea.
- Pangaea later split into:
- Laurasia (Northern landmass)
- Gondwanaland (Southern landmass)
Evidence
- Matching coastlines.
- Similar fossils found on different continents.
- Geological similarities.
- Paleoclimatic evidence.
Though initially rejected, Wegener’s theory laid the foundation for modern plate tectonics.
Earthquakes
An earthquake is the sudden shaking of the Earth’s surface caused by the release of energy within the Earth’s crust.
Important Terms
Focus (Hypocenter)
The point inside the Earth where the earthquake originates.
Epicenter
The point on the Earth’s surface directly above the focus.
Fault
A fracture in the Earth’s crust along which rocks move.
Causes of Earthquakes
1. Tectonic Causes
- Movement of lithospheric plates.
- Most common cause.
2. Volcanic Causes
- Associated with volcanic eruptions.
3. Collapse Causes
- Collapse of underground caves and mines.
4. Human-Induced Causes
- Mining activities.
- Reservoir-induced seismicity.
- Nuclear testing.
Seismic Waves
Earthquakes generate waves that travel through the Earth.
1. Primary Waves (P-Waves)
- Fastest seismic waves.
- Travel through solids, liquids, and gases.
- Reach first at seismic stations.
2. Secondary Waves (S-Waves)
- Travel only through solids.
- Slower than P-waves.
- Cannot pass through the liquid outer core.
3. Surface Waves (L-Waves)
- Travel along the Earth’s surface.
- Cause maximum destruction.
Measurement of Earthquakes
Richter Scale
- Measures the magnitude of an earthquake.
- Developed by Charles Richter.
- Logarithmic scale.
Mercalli Scale
- Measures intensity based on observed damage and effects.
Earthquake Zones of India
India is divided into four seismic zones:
Zone II
- Low damage risk.
Zone III
- Moderate risk.
Zone IV
- High risk.
Zone V
- Very high risk.
Areas in Zone V
- Jammu & Kashmir
- Himachal Pradesh
- Uttarakhand
- Northeast India
- Andaman & Nicobar Islands
- Parts of Gujarat
Why India is Earthquake-Prone
- Continuous collision between the Indian Plate and Eurasian Plate.
- Presence of active fault zones.
- Himalayan region is geologically young and unstable.
Tsunami and Earthquakes
A tsunami is a series of giant sea waves generated by undersea earthquakes, volcanic eruptions, or landslides.
Key Features
- Travels at very high speeds in deep oceans.
- Height increases near coastlines.
- Causes extensive coastal destruction.
Major Example
- Indian Ocean Tsunami (2004)
Earthquake Safety Measures
Before an Earthquake
- Prepare emergency kits.
- Identify safe places indoors.
During an Earthquake
- Drop, Cover, and Hold.
- Stay away from windows and heavy objects.
After an Earthquake
- Check for injuries.
- Avoid damaged buildings.
- Follow official advisories.
Important Facts for NDA & CDS Exams
- Alfred Wegener proposed Continental Drift Theory.
- Pangaea was the ancient supercontinent.
- Himalayas were formed by the collision of Indian and Eurasian Plates.
- P-waves travel through solids, liquids, and gases.
- S-waves travel only through solids.
- Surface waves cause maximum destruction.
- Richter Scale measures magnitude.
- Mercalli Scale measures intensity.
- India falls within seismic Zones II to V.
- Northeast India and the Himalayan region are highly earthquake-prone.
