Seismic waves

Seismic waves are produced by earthquakes in the Earth's crust. They can cause damage to structures on the Earth's surface, as well as producing tsunamis.

Cross-section showing structure of the Earth: the inner core, outer core, mantle and crust.The structure of the Earth

Properties of seismic waves

There are two types of seismic wave:

P-waves and S-waves have different properties. The table summarises these properties.

P-wavesS-wave
Type of waveLongitudinalTransverse
Relative speedFasterSlower
Can travel through Solids and liquidsSolids only

Investigating Earth structure using seismic waves

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.

S waves travelling through the Earth.

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.

P waves travelling through the Earth.P-waves are refracted as they travel through the Earth
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