There are two types of seismic wave:
P-waves and S-waves have different properties. The table summarises these properties.
|Type of wave||Longitudinal||Transverse|
|Can travel through||Solids and liquids||Solids only|
The study of seismic waves provides evidence for the internal structure of the Earth, which cannot be observed directly.
Seismic waves from large earthquakes are detected around the world. Their paths are curved as the waves refract due to the gradually changing density of the layers.
S-waves are not detected on the opposite side of the Earth – this suggests that the mantle has solid properties, but the outer core must be liquid.
P-waves are detected on the opposite side of the Earth. Refractions between layers cause two shadow zones, where no p-waves are detected – the size and positions of these shadow zones indicate there is a solid inner core.