The earliest earthquake measurements were simple descriptions of seismic events and their consequences. These results were unreliable depending on the distance between the earthquake'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 qualitatively rating observer's experiences and the damage done to structures. 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, Mercalli intensity, like the earlier descriptions, was influenced by the measurement's distance from the earthquake's...