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 decrease or change abruptly at boundaries like the mantle-core boundary due to changes in material properties.

Answer 1

The Correct Option is 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: Incorrect — The S-wave shadow zone is typically about 105° wide.
(B) P-wave shadow zones are 49° wide: Incorrect — The P-wave shadow zone is not as narrow as 49°.
(C) P-wave velocity abruptly increases downward at mantle-core boundary: Incorrect — P-wave velocity decreases at the mantle-core boundary.
(D) P-wave velocity abruptly drops downward at mantle-core boundary: Correct — At the mantle-core boundary, the P-wave velocity drops significantly due to the transition from solid mantle to liquid outer core.
Step 3: Conclusion.
The correct answer is (D) P-wave velocity abruptly drops downward at mantle-core boundary, as this is a known property of seismic waves at the core-mantle boundary.