How does shadow zone emerge?

Explanation

Earthquake waves get recorded in seismographs located at far off locations. However, there exist some specific areas where the waves are not reported. Such a zone is called the .shadow zone.. The study of different events reveals that for each earthquake, there exists an altogether different shadow zone. Seismographs located at any distance within 105° from the epicentre, recorded the arrival of both P and S-waves. However, the seismographs located beyond 145° from epicentre, record the arrival of P-waves but not that of S-waves. Thus, a zone between 105o and 145° from epicentre was identified as the shadow zone for both the types of waves. Figures given below show the shadow zones of P- and S-waves.

The entire zone beyond 105° does not receive S-waves. The shadow zone of S-wave is much larger than that of the P-waves. The shadow zone of P-waves appears as a band around the earth between 105° and 145° away from the epicentre. The shadow zone of S-waves is not only larger in extent but it is also a little over 40 per cent of the earth surface.