The correct option is The entire zone beyond 105° from the epicentre does not receive S-waves..
Explanation
Earthquake waves are recorded by seismographs located at various distances from the epicentre. However, due to the varying density and state (solid/liquid) of the Earth's interior layers, waves are reflected or refracted. This creates specific areas on the Earth's surface where waves are not recorded, known as the 'shadow zone'.Statement-wise Analysis:
- Statement The shadow zone for P-waves is larger than that for S-waves. is Incorrect. The shadow zone of S-waves is significantly larger than that of P-waves. While the P-wave shadow zone is restricted to a specific band, the S-wave shadow zone covers a vast portion of the globe.
- Statement The entire zone beyond 105° from the epicentre does not receive S-waves. is Correct. S-waves (Secondary waves) cannot travel through liquid materials. Since the Earth's outer core is liquid, S-waves are stopped at the core-mantle boundary. Consequently, the entire zone beyond 105° from the epicentre does not receive S-waves.
- Statement The shadow zone of S-waves covers less than 20 % of the earth's surface. is Incorrect. The shadow zone of S-waves covers slightly more than 40 % of the Earth's surface, which is much larger than the 20 % stated.
- Statement P-waves are not recorded in the zone between 105° and 180°. is Incorrect. The shadow zone for P-waves is specifically located between 105° and 145° from the epicentre. Beyond 145°, P-waves are recorded again because they are refracted (bent) through the liquid outer core and solid inner core. Thus, P-waves are indeed recorded between 145° and 180°.
Key Takeaway:
The S-wave shadow zone extends continuously beyond 105° because S-waves cannot pass through the liquid outer core. The P-wave shadow zone is a specific band between 105° and 145° caused by the refraction of P-waves.