What is the shadow zone in earthquakes.

Question

P and S waves are seismic waves that travel through the earth, as opposed to the surface waves which travel above the earth. P waves, also known as Primary waves travel in compression. S waves, also known as secondary waves, travel slower than P waves and can only move through solids. As any kind of wave travels, it will refract (bend) due to differences in density.

The earth has different zones based on density differences and the way seismic waves refract within them; from the top the zones include lithosphere (crust and rigid mantle), asthenosphere, stiffer mantle, outer core and inner core. These zones become more dense and hotter as depth increases. The outer core has been determined to be composed of melted rock, hence it is liquid and S waves can't travel through the outer core.

The combination of seismic waves bending, and the S-waves stopping at the liquid outer core, results in a zone on the earth where neither P nor S waves can be detected by seismographs. This zone occurs in a band of approximately 103⁰ to 143⁰ from the earthquake epicenter. This is known as the shadow zone.

Answer 1

Yes, the shadow zones are where the seismic waves aren't detected. To expand on the first answer though, the S shadow zone is bigger because those waves can't pass through the liquid outer core, whereas the P waves can.

The 103° to 142° shadow zone is actually the P zone, and the S shadow zone goes from 103° on one side of the epicenter to 103° on the other. That means the P shadow zone is broken into two segment, both 39° wide, whereas the S shadow zone is 154° total.