The correct answer is option B, moment magnitude scale.
Moment magnitude scale basically measures the magnitude of an earthquake or the energy released by the earthquake.
The energy is measured using thermodynamic phenomenon. The energy released is in the form of elastic energy represented by “dU”. dU is directly proportional to the product of excess pressure (pe) in the magma chamber and volume decrease (−dVc) of the chamber
Thus, dU = −pedV