In the study of natural disasters — be they tornadoes, hurricanes, snowpacolyses or Florida on a weekday — the event’s magnitude is just as vital to our understanding as its duration and frequency. Hurricanes and tornadoes are measured by class, blizzards along the Winter Wonderland-Killstorm demarcation. Earthquakes, of course, are measured by how much energy they release — a system better known as the Richter Scale.
How It Works
Officially known as the Richter magnitude scale, the Richter scale is used to measure the strength of a quake and assign it a single quantifiable number indicating its relative magnitude. The system operates on a base-10 logarithmic scale, measuring the amplitude of seismic waves recorded upon a seismograph. Basic seismographs, or seismometers, use a dampened inertial mass held in place relative to the rest of the instrument (think: a hanging pendulum, suspended over a recording surface). This weight is less likely to move when the ground trembles on account of its inertia so seismologists can measure the motion of the ground by comparing the movement of the frame versus the weight along three axis — North-South, East-West and vertical.
For the rest of the story: http://www.gizmodo.com.au/2013/05/tracking-tremors-a-brief-history-of-the-richter-scale/