Investigating Earth's structure

Infrasound can be used to investigate the internal structure of our planet, just like ultrasound is used for foetal scanning. Earthquakes produce very powerful seismic waves that can be classed as infrasound waves.

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

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 only travel through solids. 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 can travel through solids and liquids. 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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