Earthquakes and Tsunamis: Causes and Indian Vulnerability

TOPIC CLASSIFICATION

Subject: Physical Geography & Disaster Management Sub-area: Natural Hazards - Earthquakes, Tsunamis Difficulty: Medium Weightage: Moderate (1-2 Prelims + Mains on DM)

EXAMINER REASONING

1. Trap: Thinking all tsunamis are caused by earthquakes (they can also be caused by underwater volcanic eruptions, landslides, and meteor impacts).
2. Most confused: Epicentre vs Hypocentre (Focus) - epicentre is point on surface directly above focus.
3. Key anchor: Plate tectonics - Indian plate moving north at ~5 cm/year → constant stress against Eurasian plate.
4. Current affairs hook: Turkey-Syria earthquake (Feb 2023) - 50,000+ dead; Nepal earthquakes (2015, 2023); Japan tsunami (2011); India's NDMA guidelines for earthquake preparedness.
5. Mains hinge: "India's vulnerability to earthquakes and tsunamis is shaped by its geological setting. Discuss the mitigation strategies adopted and their limitations."

Core Concept

Causes of Earthquakes

• Plate Tectonics: Earth's lithosphere divided into plates - movement along plate boundaries releases energy
• Faulting: Sudden slip along a fault → seismic waves (P-waves, S-waves, Surface waves)
• Types of Boundaries: Convergent (collision), Divergent (spreading), Transform (slipping)
• Induced Seismicity: Reservoir-triggered (Koyna), mining, geothermal, hydraulic fracturing

Measuring Earthquakes