Modified Mercalli Intensity Scale

A twelve-degree scale rating the intensity of ground shaking and damage an earthquake produces AT A PARTICULAR PLACE, distinct from a magnitude scale's single reading of the earthquake's own released energy. Giuseppe Mercalli published a ten-degree intensity scale in 1902, building on the earlier Rossi-Forel scale; Harry Wood and Frank Neumann revised, translated and condensed it into English in 1931 as the modified Mercalli scale, and Charles Richter, the seismologist the magnitude scale is named for, revised it again in 1956. Because intensity is read off felt and observed effects at a given site, one earthquake produces one magnitude but many different Mercalli intensities depending on distance, ground conditions and building stock, which is why the scale still matters for a quake, such as the 1755 Lisbon earthquake, that struck long before any instrument could record a magnitude directly.