Body wave magnitude
) 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 the speed of sound, 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 - 6.5mb, with the figure staying the same even when the moment magnitude may be higher.