Seismology

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.

Step 1: Understanding the Richter Scale.
The Richter scale is logarithmic. This means that each increase of 1 unit on the scale corresponds to a tenfold increase in the amplitude of the earthquake. Additionally, the intensity of an earthquake is proportional to the square of the amplitude. Therefore, the intensity of an earthquake increases by a factor of 100 for each unit increase in magnitude.
Step 2: Calculation of Intensity Ratio.
For magnitude 8 and 5, the difference in magnitude is . Using the formula for the intensity ratio based on the Richter scale: Step 3: Conclusion.
The intensity of an earthquake of magnitude 8 is 1000 times greater than the intensity of an earthquake of magnitude 5.

Step 1: Understanding Shear Waves.
Shear waves (S-waves) are a type of seismic wave that move through the Earth’s interior. They can only travel through solid materials, not liquids.
Step 2: Analyzing the options.
(A) upper continental crust: Incorrect — S-waves can travel through the solid upper continental crust.
(B) upper mantle: Incorrect — The upper mantle is solid and S-waves can travel through it.
(C) lower mantle: Incorrect — The lower mantle is solid and S-waves can also travel through it.
(D) outer core: Correct — The outer core is liquid, and S-waves cannot travel through liquids.
Step 3: Conclusion.
The correct answer is (D) outer core, as shear waves cannot travel through liquids.