There are no P-waves or S-waves received in the P-wave shadow zone because of the Earth's liquid outer core and how seismic waves travel through different materials. S-waves cannot travel through the liquid outer core at all, so they are completely stopped and do not appear beyond the shadow zone. P-waves, on the other hand, can travel through solids and liquids but they slow down significantly and are refracted (bent) when they pass through the liquid outer core. This refraction bends the P-wave paths away from certain regions on the Earth's surface, creating a shadow zone where no direct P-waves arrive. Thus, the P-wave shadow zone appears as a ring on the Earth's surface where no direct body waves (P or S) are detected because S-waves cannot penetrate the liquid outer core and P-waves are bent away due to refraction at the core- mantle boundary. This shadow zone typically ranges from about 103 to 142 degrees away from the earthquake epicenter.
