Transmission of seismic waves: Seismic waves are the route taken by the tremor of the earthquake during the its occurrence. These waves are of three types. Primary, secondary and surface waves. Based oh the seams and motion of seismic waves, the information about the inner parts of the Earth is found. These waves move straight in the same density part.
But by marking these waves on the earthquake centers, it came to be known that these waves do not move in a straight direction but reflect the shape of the curved path. It proves that the density of the inner parts gets varied. As a result, their path also turns curved. Since the density towards the internal part increases, these waves (P and S) in the core become concave towards tjie surface.
S waves do not pass through liquid and they become extinct at more than 2900 km depth. It proves that the depth more than 2900 km is in a liquid state, which is broad around the center. With varying density of rocks, there is more difference in the speed of the waves at three places.
This motion of seismic waves and the variations found in them are depicted through the following picture: