There are 3 types of earthquake waves: P, S, and surface waves. The P and S waves are called BODY waves because they travel within the body of the earth. The surface waves include Rayleigh and Love waves.
P-waves, also known as Primary waves and compressional waves, travel fastest. They can move through solids and liquids, like the molten outer core. S-waves, also known as Secondary waves, travel slower and can only move through solid zones within the earth. As these body waves move through the earth, they are refracted (bent) as they travel through rock layers with different densities. The density within the earth increases with depth. As a result of the waves refracting and the presence of a liquid outer core, there is a zone on the earth, ranging from 1030 to 1430 from the earthquake epicenter called the SHADOW ZONE. If there is a seismograph located in this band of shadow, it will not detect an earthquake, no matter how intense it is.
