It is related to the energy released during the earthquake. This scale is an improvement of the Richter magnitude scale, which American seismologist Charles F. Richter invented in 1935. In both scales, the stronger the earthquake is, the higher is the magnitude. The Richter and moment magnitudes are nearly identical for most earthquakes with a magnitude less than 7. However, moment magnitude measures the strongest earthquakes more accurately.
Scientists can determine moment magnitude in two ways.
In the first method, they measure the length and depth of the earthquake fault and the movement of rock at the fault. A fault is a fracture in the earth's rocky outer shell where sections of rock repeatedly slide past each other. In the second method, scientists use data from a seismograph, a device that records ground movements. Richter magnitude is based on seismographic data. The main difference between the two scales lies in the frequencies of the movements that are recorded.