🔹 What is an Earthquake?

An earthquake is the sudden shaking or vibration of the Earth’s surface caused by the release of energy from within the Earth’s crust.

🔹 Causes of Earthquakes

1. Tectonic Causes (Main Cause)

• Due to movement of tectonic plates
• Occurs along plate boundaries (fault lines)
• Explained by Plate Tectonics

2. Volcanic Causes

• Occur due to volcanic eruptions

3. Human-Induced Causes

• Mining
• Reservoir construction
• Nuclear explosions

🔹 Key Terms

• Focus (Hypocenter): Point inside Earth where earthquake originates
• Epicenter: Point on Earth’s surface directly above the focus
• Seismic Waves: Energy waves that travel through Earth

🔹 Types of Seismic Waves

1. P-Waves (Primary)
   • Fastest
   • Travel through solids, liquids, gases
2. S-Waves (Secondary)
   • Slower than P-waves
   • Travel only through solids
3. L-Waves (Surface Waves)
   • Most destructive
   • Travel on Earth’s surface

🔹 Measurement of Earthquakes

• Measured using Seismograph
• Magnitude scale: Richter Scale
• Intensity scale: Mercalli Scale

🔹 Effects of Earthquakes

• Loss of life and property
• Landslides
• Tsunami
• Soil liquefaction
• Damage to infrastructure

🔹 Earthquake Zones in India

India is divided into 4 seismic zones:

• Zone II – Low risk
• Zone III – Moderate
• Zone IV – High
• Zone V – Very high (e.g., Himalayas, Northeast)

🔹 Earthquake Management

• Construct earthquake-resistant buildings
• Disaster preparedness plans
• Early warning systems
• Public awareness