Earthquake Size (Magnitude)

Earthquakes have complex and variable rupture processes and seismic wave forms. In addition, seismometer technologies are always evolving, becoming more sensitive to movements within the Earth. Because of this, there are different methods for measuring
the magnitude of an earthquake and each returns a slightly different number when used to estimate the energy released in an earthquake.

The Modified Mercalli is the oldest of the three, and uses a subjective rating system based on the shaking felt and damages incurred during an earthquake. The Richter Scale measures the amplitude, or maximum extent of vibration, of an earthquake. This scale is only really accurate for small to medium earthquakes within 600km from a recording station. The last scale, the Moment Magnitude Scale, is the most precise of the three and has the capability to measure much larger and more distant earthquakes. This scale allows us to equate the magnitude of the earthquake to actual energy released from an earthquake. The chart below can be use for comparison of the three scales.

Modified Mercalli Scale and the Richter Magnitude scale