Seismic moment in the context of "Seismologist"

Seismic moment is a quantity used by seismologists to measure the size of an earthquake. The scalar seismic moment ${\displaystyle M_{0}}$ is defined by the equation${\displaystyle M_{0}=\mu AD}$, where

• ${\displaystyle \mu }$ is the shear modulus of the rocks involved in the earthquake (in pascals (Pa), i.e. newtons per square meter)
• ${\displaystyle A}$ is the area of the rupture along the geologic fault where the earthquake occurred (in square meters), and
• ${\displaystyle D}$ is the average slip (displacement offset between the two sides of the fault) on ${\displaystyle A}$ (in meters).

${\displaystyle M_{0}}$ thus has dimensions of torque, measured in newton meters. The connection between seismic moment and a torque is natural in the body-force equivalent representation of seismic sources as a double-couple (a pair of force couples with opposite torques): the seismic moment is the torque of each of the two couples. Despite having the same dimensions as energy, seismic moment is not a measure of energy. The relations between seismic moment, potential energy drop and radiated energy are indirect and approximative.