When an earthquake occurs, the fault movement generates seismic waves of energy that spread outwards through the ground in all directions simultaneously.
Earthquakes create several distinct types of wave with different velocities. When these are measured at seismic observatories, their different travel times help scientists to locate the source of the earthquake.
In geophysics, the refraction or reflection of seismic waves is used for research into the structure of the Earth's interior, and man-made vibrations are often generated to investigate shallow, subsurface structures.
Scientists use wave propagation to determine magnitude , depth and locations of an earthquake. This video from GNS Science explains how it's done.
How fast the earthquake's waves spread depends on the type of wave and the density and elasticity of the ground they are travelling through. Velocity also tends to increase with depth. Research by GNS Science indicates waves may travel at up to approximately 8,000 m/s in the Earth’s crust and around 13,000 m/s in the deep mantle.
Seismic waves are grouped into two types – body waves and surface waves.
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