Q115 / 270 · NDA 2025 (Phase 2) · General Ability
Which of the following statements with reference to shadow zones in an event of an earthquake is/are correct?
1. Zone between 105° and 145° from epicentre was identified as the shadow zone for both P-waves and S-waves
2. The shadow zone of P-waves is much larger than that of the S-waves
Select the answer using the code given below:
1. Zone between 105° and 145° from epicentre was identified as the shadow zone for both P-waves and S-waves
2. The shadow zone of P-waves is much larger than that of the S-waves
Select the answer using the code given below:
- Correct answerA1 only
- B2 only
- CBoth 1 and 2
- DNeither 1 nor 2
Solution
Seismographs located at any distance within $105^{\circ}$ from the epicentre record the arrival of both P-waves and S-waves. However, seismographs located beyond $145^{\circ}$ from the epicentre record the arrival of P-waves, but not S-waves.
Thus, the zone between $105^{\circ}$ and $145^{\circ}$ from the epicentre is identified as the shadow zone for both types of waves. Hence, statement 1 is correct.
The entire zone beyond $105^{\circ}$ does not receive S-waves. The shadow zone of S-waves is much larger than that of P-waves, covering over $40\%$ of the earth's surface. Hence, statement 2 is incorrect.
Answer: 1 only
Thus, the zone between $105^{\circ}$ and $145^{\circ}$ from the epicentre is identified as the shadow zone for both types of waves. Hence, statement 1 is correct.
The entire zone beyond $105^{\circ}$ does not receive S-waves. The shadow zone of S-waves is much larger than that of P-waves, covering over $40\%$ of the earth's surface. Hence, statement 2 is incorrect.
Answer: 1 only
Hence, the correct answer is option: 'A'.