S-wave shadow zone
Topic: Interior of the Earth: Earthquakes, Volcanoes and the Layered Earth · NCERT: Class 11, Ch 3 "Interior of the Earth"
Meaning
The S-wave shadow zone is the whole area more than about 105° from the epicentre where no S-waves arrive. It covers a little over 40 per cent of the earth's surface. S-waves pass through solids only. When they reach the outer core, which starts at about 2,900 km depth, they stop. The missing S-waves are the main proof that the outer core is liquid. Every earthquake has its own shadow zone, which moves with the epicentre.
Example
For the Bhuj earthquake of 2001 in Gujarat, stations on the far side of the earth, in the south-east Pacific, recorded P-waves but no S-waves at all.
Don't confuse with
- P-wave shadow zone: this is only the band between 105° and 145°, caused by P-waves bending at the core. P-waves come back to the surface beyond 145°, but S-waves never do.