P and S waves' paths through Earth

The speed of P waves and S waves increases as they travel deeper into the Earth’s mantle.

They travel through the Earth in curved paths, but they change direction suddenly when they pass through the boundary between substances in different states.

The diagrams show what happens when P waves and S waves pass through the Earth.

P waves

  • Longitudinal
  • Fast moving
  • Travel through liquids and solids
Diagram showing the curved path of P waves through the Earth. They travel through the mantle, the liquid outer core and the solid inner core.P waves can pass through the Earth's core

S waves

  • Transverse
  • Slower moving than P waves
  • Travel through solids only
Diagram showing the curved path of S waves through the Earth. They travel through the mantle but cannot pass through the liquid outer core.S waves do not pass through the Earth's core

S waves cannot pass through the liquid outer core, but P waves can. The waves are refracted as they travel through the Earth due to a change in density of the medium. This causes the waves to travel in curved paths. When the waves cross the boundary between two different layers, there is a sudden change in direction due to refraction.

Question

Compare the properties of P waves, S waves and surface seismic waves.

A surface wave travels along the surface of the Earth. It is the slowest of the three types of seismic wave. Surface waves usually have larger amplitude than the other waves and cause the most damage.

A P wave is a longitudinal wave and travels the fastest. It can travel through solids and liquids.

An S wave is a transverse wave and travels slower than a P wave, thus arriving after the P wave. S waves can only travel through solids, and as a result do not travel through the liquid core of the Earth.