Question 6 of 9intermediate💡 UnderstandShort Answer2 marks

Why do earthquake waves develop shadow zone?

Correct Answer

Earthquake waves develop shadow zones because they travel through materials with different densities inside the Earth. As the waves propagate, their velocity changes and their direction changes through reflection or refraction when they encounter materials with varying densities.

This causes certain waves to not reach specific areas. For S-waves, the entire zone beyond 105° from the epicentre does not receive them, creating a large shadow zone. For P-waves, a band between 105° and 145° from the epicentre forms the shadow zone. Thus, different types of waves create different shadow zones due to their varying propagation characteristics through the Earth's interior.

Exercise: EXERCISES | Q: 2(iii) | (Page 9)
For More Understanding

Explanation

The textbook explains that shadow zones develop because earthquake waves interact differently with materials of varying densities inside the Earth. The context states that 'The velocity of waves changes as they travel through materials with different densities' and 'Their direction also changes as they reflect or refract when coming across materials with different densities.' This differential behaviour of P-waves and S-waves creates distinct shadow zones. S-waves cannot travel through liquid, creating a larger shadow zone beyond 105°, while P-waves create a band-shaped shadow zone between 105° and 145° from the epicentre.

Solution Steps

  1. Step 1: Identify that waves travel through materials with different densities inside the Earth.

  2. Step 2: Explain that velocity and direction of waves change through reflection and refraction.

  3. Step 3: Conclude that this causes certain areas (shadow zones) to not receive specific waves.

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