Question

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

Answer 1

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 = 2/3 log(M_0) - 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.