Hi Yurom!

Seismic Waves occurs when earthquake is formed and spreads in all directions through the Earth's Interior which are recorded by the Seismic Stations.

Seismic Velocities depend on the factors of Material Properties such as composition, mineral phase, structure, temperature and pressure through which the Seismic Waves pass.

Below are the layers of the Earth's Interior:

• First Layer is the Crust. It is less dense.
• Second Layer is the Mantle which is also known as the Low Velocity Zone.
• Then comes the Core which is divided as Outer Core and Interior Core.

Hope this is helpful!

All the best!