# What is the seismic moment of an earthquake and what is it used for?

May 27, 2016

Seismic moment is measure of the size of an earthquake and it is used in order to calculate moment magnitude.

#### Explanation:

Seismic moment is an important value for earthquake magnitude determination. Seismic moment , ${M}_{0}$, is related with the rigidity of the eartquake source region, $\mu$, area of the fault plane, $A$ and average displacement, $D$. Equation of ${M}_{0}$ can be seen as below,

${M}_{0} = \mu A D$

By using ${M}_{0}$ moment magnitude, ${M}_{w}$ can be calculated,

${M}_{w} = \frac{2}{3} \log \left({M}_{0}\right) - 10.7$.

Determining ${M}_{w}$ is important since, ${M}_{w}$ cannot saturate unlike other magnitude scale. This property of ${M}_{w}$ comes from the feature of ${M}_{0}$. Other magnitude types are depended with certain part of seismic records. Seismic records, however, can satured if the magnitude of the earthquake is bigger than a certain magnitude. Because of that ${M}_{0}$ has a vital role on modern seismology.

The seismic moment can be also interpreted in terms of the strain energy released in earthquakes.