The correct option is It appears as a band around the earth between 105° and 145° away from the epicentre.
Explanation
Seismic waves travel through the Earth's interior and are recorded by seismographs. Due to variations in the density and physical state (solid or liquid) of the Earth's layers, these waves undergo reflection and refraction. Specific areas on the Earth's surface where waves from a particular earthquake are not recorded are termed "shadow zones."Detailed
- It appears as a band around the earth between 105° and 145° away from the epicentre. is Correct: The shadow zone for P-waves appears as a distinct band around the Earth between 105° and 145° away from the epicentre. This phenomenon occurs because P-waves are refracted (bent) when they enter and exit the liquid outer core.
- It covers more than 40 % of the earth's surface. is Incorrect: It is the shadow zone of S-waves, not P-waves, that covers more than 40 % of the Earth's surface. The S-wave shadow zone extends continuously over the entire region beyond 105°.
- It is larger than the shadow zone of S-waves. is Incorrect: The shadow zone of S-waves is larger than that of P-waves. S-waves are shear waves and cannot travel through the liquid outer core; therefore, they are not recorded anywhere beyond 105°. P-waves, being compressional, can pass through the core and reappear beyond 145°.
- No P-waves are recorded beyond 105° from the epicentre. is Incorrect: P-waves are recorded beyond 145° from the epicentre. The absence of P-waves is restricted only to the band between 105° and 145°.
Key Takeaway:
The P-wave shadow zone is a specific band (105°-145°) resulting from refraction, whereas the S-wave shadow zone is a vast region (entire area beyond 105°) resulting from the absorption of S-waves by the liquid outer core.