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Earthquake magnitude is typically a measurement of ground motion, which is then expressed as a value on the Richter scale, developed in 1935 by Charles Richter. It is based on powers of ten, meaning that an earthquake measuring 5 on the Richter scale has a recorded seismograph amplitude ten times greater than one measuring 4. Magnitude can also be translated into the seismic energy released by an earthquake, measured in joules (J). Here an increase of one on the Richter scale represents an over thirty-fold increase in the amount of seismic energy. This enables the power of earthquakes to be compared with other energy sources and vice versa.