Cost overruns and budget cuts suspended drilling in 1988 Other deep holes are planned. Volcanic activity Materials are brought up from below. High pressure laboratory experiments to determine which minerals can exist at high pressures like that of the great depths of the mantle. Study of seismic waves generated by earthquakes and nuclear explosions - This is the most important method of determining the internal structure of the Earth. Wave velocity depends on the density and elasticity of the rock.
Seismic waves travel faster in denser rock.
The velocity of seismic waves increases with depth . P-waves can travel through all of the layers of the Earth because they can travel through both solids and liquids . On the other hand, S-waves can travel through the Earth' s crust and mantle, but they STOP when they reach the Earth's core. The size of the shadow zone gives us a good idea of the size and depth of the Earth's outer liquid core.