Seismic moment

Summary

The seismic moment $M_0$ of an earthquake is a product of three factors. They are the shear modulus of the rock, the area of the fault that slipped, and the average slip. It measures the size of an earthquake by its physical source, not by the reading of an instrument. It is the size of the force couples equivalent to the slip, and it is measured in newton metres. The moment magnitude scale is defined from it.