Question

In Figures A, B, C is three points on the earth's surface. Analyse their locations with respect to epicenter and shadow zones

Answer 1

A, B, C are the points on the surface of the earth.

1. 'A' point is located with 105° from the epicentre, therefore P waves and S waves reach 'A' point. The seismograph at 'A' point records both waves, therefore 'A' point is not in the shadow zone.
2. 'B' point is in the shadow zone because both the waves do not reach there. P waves pass through all mediums, they experience refraction as they pass on one medium to another. The seismograph records P waves, which is located away from the 'B' point. But P waves are not recorded in an area between 105 and 140° from epicentre. The S waves also do not reach here. Therefore, it is called the 'Shadow zone' of Earthquake waves.
3. 'C' point is in the area of the shadow zone of 'S' waves, that in within 140°. P waves reach beyond 140°. Since 'S' waves do not reach here, it is called the 'Shadow zone of S waves'.