Mercalli

Mercalli refers most commonly to the Mercalli intensity scale, a qualitative scale used in seismology to describe earthquake effects on people, structures, and the environment. It is named after Giuseppe Mercalli, an Italian priest and volcanologist (1850–1914), who developed the original scale in the early 20th century.

The original Mercalli intensity scale, published in 1902, used Roman numerals I through XII to categorize observed effects rather than ground motion. In 1931, the scale was revised into the more widely used Modified Mercalli Intensity (MMI) scale by Harry O. Wood and Frank Neumann, adapting descriptions to modern building practices and data collection. The MMI scale remains a standard tool for documenting the intensity of historical earthquakes and for describing their impacts in narrative form.

Each level of the Mercalli scale corresponds to qualitative descriptions of what people experience, how structures perform, and what environmental changes occur during and after an event. Observations can be influenced by distance from the epicenter, local soil and rock conditions, construction quality, and population density, which can lead to variations in assigned intensity for the same earthquake.

While instrumental measures such as magnitude scales quantify energy release, the Mercalli scale provides a complementary, experience-based assessment of seismic impact. Today, MMI remains widely used in historical earthquake reports and applied seismology, particularly when evaluating human and structural effects in lieu of direct instrumental readings.