Seismic waves - Higher
Shock waves travelling through the Earth, usually caused by an earthquake. are produced by earthquakes in the Earth鈥檚 crust. They can cause damage to structures on the Earth鈥檚 surface, as well as A large destructive wave caused by earthquakes, volcanic activity or landslides under water..
Properties of seismic waves
There are two types of seismic wave:
- P waves, which are A wave that moves in the same direction as the way in which the particles are moving.
- S waves, which are A wave that moves in a direction at right angles to the way in which the particles are vibrating.
P waves and S waves have different properties. The table summarises these properties:
| P waves | S waves | |
| Type of wave | Longitudinal | Transverse |
| Relative speed | Faster | Slower |
| Can travel through | Solids and liquids | Solids only |
| Type of wave | |
|---|---|
| P waves | Longitudinal |
| S waves | Transverse |
| Relative speed | |
|---|---|
| P waves | Faster |
| S waves | Slower |
| Can travel through | |
|---|---|
| P waves | Solids and liquids |
| S waves | Solids only |
Investigating the Earth's 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 using A machine that detects seismic waves caused by earthquakes.. Their paths are usually curved 鈥 this is due to the fact that the waves are Process by which a wave changes speed and sometimes direction upon entering a denser or less dense medium, eg a light ray changes direction when refracted by a lens. as they meet the gradually changing density of the layers within the Earth.
S waves are not detected on the opposite side of the Earth 鈥 this suggests that the mantle has solid properties, but the The Earth's outer core is a fluid layer that sits above the solid inner 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 鈥 the size and positions of these shadow zones indicate there is a solid inner core.