Discuss how do scismic waves suggest …

• Seismic waves can tell us a lot about the internal structure of the Earth because these waves travel at different speeds in different materials.
• Reflection causes P and S waves to rebound whereas refraction makes waves move in different directions.
• The variations in the direction of these waves are inferred with the help of their record on seismograph.
• Change in densities greatly varies the wave velocity. By observing the changes in velocity, the density of the earth as a whole can be estimated. By the observing the changes in direction of the waves (emergence of shadow zones), different layers can be identified.
• For both kinds of waves, the speed at which the wave travels also depends on the properties of the material through which it is traveling.
• Scientists are able to learn about Earth’s internal structure by measuring the arrival of seismic waves at stations around the world.
• For example, we know that Earth’s outer core is liquid because s-waves are not able to pass through it; when an earthquake occurs there is a “shadow zone” on the opposite side of the earth where no s-waves arrive.
• Similarly, we know that the earth has a solid inner core because some p-waves are reflected off the boundary between the inner core and the outer core.
• By measuring the time it takes for seismic waves to travel along many different paths through the earth, we can figure out the velocity structure of the earth.
• Abrupt changes in velocity with depth correspond to boundaries between different layers of the Earth composed of different materials.

The structure of Earth’s deep interior cannot be studied directly. But geologists use seismic (earthquake) waves to determine the depths of layers of molten and semi-molten material within Earth. Geologists are now using these records to establish the structure of Earth’s interior.