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:
- A.1 only
- B.2 only
- C.Both 1 and 2
- D.Neither 1 nor 2
Correct answer
Explanation
The correct answer is A, 1 only. The band between 105° and 145° from the epicentre receives neither P-waves nor S-waves, but it is the S-wave shadow zone that is much larger, so statement 2 is wrong.
Seismographs far from an earthquake show where body waves fail to arrive. P-waves travel through solids and liquids, but they bend sharply on entering the liquid outer core, which leaves a ring between about 105° and 145° from the epicentre where they are not recorded. S-waves cannot pass through liquids at all, so they are missing everywhere beyond about 105°. This means the band from 105° to 145° gets neither wave, while the whole area beyond 105° lacks S-waves. The S-wave shadow was the key evidence that the outer core is liquid.
B is wrong because statement 2 reverses the facts: the S-wave shadow zone, covering everything beyond 105°, is far larger than the P-wave shadow zone. C is wrong because statement 2 is false. D is wrong because statement 1 is correct.
Exam tip: P-wave shadow 105°–145°; S-wave shadow everything beyond 105°; S-waves stop at the liquid outer core.
Practice Questions
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