Here's why:
* Seismic waves travel through the Earth's interior. There are two main types: P-waves (primary waves, compressional) and S-waves (secondary waves, shear).
* P-waves can travel through solids and liquids, while S-waves can only travel through solids.
* The Earth's core is mostly liquid. When P-waves reach the liquid outer core, they refract (bend) and continue traveling through the core. However, S-waves cannot travel through the liquid outer core and are stopped.
* This creates a "shadow zone" on the opposite side of the Earth from the earthquake's epicenter. This zone does not receive any direct S-waves and only receives refracted P-waves, which arrive later and with less intensity.
This shadow zone is crucial for understanding the Earth's interior structure. By studying the patterns of seismic waves, scientists have been able to deduce the presence of the liquid outer core and the solid inner core.
