Describe how P-waves and S-waves give scientists enough data to develop a model of Earth's Layers

S - waves travel at a speed of 1 to 8 km/sec usually. The lower values of the speed of S-wave is due to the loose and unconsolidated sediment of earth while the higher values of the speed of S-wave is due to its nearness or existence in the mantle of earth. Also S-wave cannot travel in liquid or gaseous medium due to their inability to transmit shear stress.

The velocity of a p-wave depends on two physical features: a) elastic properties of the medium and b) density of the medium. Thus if we get to know the value of these two property we can estimate the material type of the medium. P wave can travel in solid, liquid and gaseous medium.