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.