# Body wave magnitude

Body wave magnitude (${\displaystyle m_{b}}$) is a way of determining the size of an earthquake, using the amplitude of the initial P-wave to calculate the magnitude. The P-wave is a type of body wave that is capable of traveling through the earth at a velocity of around 5 to 8 km/s, and is the first wave from an earthquake to reach a seismometer. Because of this, calculating the body wave magnitude can be the quickest method of determining the size of an earthquake that is of a large distance from the seismometer.

Limitations in the calculation method mean that body wave magnitude saturates at around 6-6.5 ${\displaystyle m_{b}}$, with the figure staying the same even when the moment magnitude may be higher.