Question

P and S waves originate at earthquake focus and travel through the earth. Which of the following statements for these waves is/are correct?

• A. S-wave shadow zone is 154° wide
• B. P-wave shadow zones are 49° wide
• C. P-wave velocity abruptly increases downward at mantle-core boundary
• D. P-wave velocity abruptly drops downward at mantle-core boundary

Hint:

Seismic wave velocities change abruptly at boundaries like the mantle-core boundary due to the change in material state, which affects wave propagation.

Answer 1

The Correct Option is A, D

Step 1: Understanding the question.
The question asks about the characteristics of P and S waves and their behavior as they travel through the Earth’s layers.
Step 2: Analyzing the options.
(A) S-wave shadow zone is 154° wide: Correct — The S-wave shadow zone is approximately 154°, which is the region where S-waves cannot be detected due to their inability to travel through the liquid outer core.
(B) P-wave shadow zones are 49° wide: Incorrect — The P-wave shadow zone is typically wider, about 103°, due to the refraction of P-waves as they pass through the liquid core.
(C) P-wave velocity abruptly increases downward at mantle-core boundary: Incorrect — P-wave velocity actually decreases at the mantle-core boundary due to the transition from solid mantle to liquid outer core.
(D) P-wave velocity abruptly drops downward at mantle-core boundary: Correct — P-wave velocity significantly drops at the mantle-core boundary as the P-waves transition into the liquid outer core.
Step 3: Conclusion.
The correct answer is (A), (D), as these statements are correct based on seismic wave behavior at the core-mantle boundary.