The earliest earthquake measurements were simple descriptions called intensity ratings. These results were unreliable depending on the distance between the quake's source (epicenter), and the people evaluating the event.

A more systematic approach was developed by an Italian seismologist, Guiseppe Mercalli in 1902. He gauged earthquake intensity by measuring the damage done to buildings. The United States Coast and Geodetic Survey adapted his method, which they called the modified Mercalli Scale, dividing the measurements into 12 categories: level II was "felt by persons at rest," but at level VII it was "difficult to stand." Level X caused most buildings to collapse, and level XII, the most intense, combined ground fissures with tsunamis (tidal waves) and almost total destruction. Despite the specific detail of descriptions, this method, like the intensity ratings, was influenced by the measurement's distance from the earthquake's epicenter. Seismologists needed a way to determine the size...