Giuseppe Mercalli - The Intensity Scales Proposed By Mercalli

The Intensity Scales Proposed By Mercalli

Mercalli was the author of two intensity scales. The first of these (Mercalli, 1883), was according to Davison (1921) a mere adaptation of the Rossi–Forel scale. It has six degrees unlike the ten degrees of the Rossi–Forel scale. Nowadays this scale is largely forgotten. Mercalli's second scale (Mercalli, 1902), has ten degrees (unlike the 12 degrees that are wrongly and largely publicited in many internet webpages) and is basically an expansion of the descriptions states in the Rossi–Forel scale.

In 1904 the ten-degree Mercalli scale was expanded to twelve degrees by Italian physicist Adolfo Cancani; he added two extra degrees at the top of the scale (the degrees XI (catastrophe) and XII(enormous catastrophe)). It was later completely re-written by the German geophysicist August Heinrich Sieberg and became known as the Mercalli–Cancani–Sieberg (MCS) scale. The Mercalli–Cancani–Sieberg scale was later modified and published in English by Harry O. Wood and Frank Neumann in 1931 as the Mercalli–Wood–Neumann (MWN) scale. It was later improved by Charles Richter, the father of the Richter magnitude scale. The scale is known today as the Modified Mercalli scale or Modified Mercalli Intensity scale, and abbreviated MM or MMI.