Modified Mercalli intensity scale

A twelve-level scale describing earthquake shaking and damage at a location from observed effects, rather than instrumental measurements.

Mercalli intensity: A measure of earthquake shaking at a particular place, inferred from its effects on people, buildings, and the landscape. The scale is a standardized version of this location-specific measure.
Richter magnitude scale: A logarithmic scale originally developed to quantify earthquake size from seismograph recordings. Unlike this scale, it assigns one magnitude to an earthquake rather than local shaking levels.
Earthquake engineering: The study and practice of designing structures to withstand earthquake ground motion. Intensity observations help relate actual shaking to structural performance.
Giuseppe Mercalli: An Italian volcanologist and seismologist who devised an earthquake intensity scale published in 1902. His original scale provided the basis for later revisions.
Macroseismic intensity: An estimate of earthquake effects derived from observations rather than direct instrumental records. This broader practice supplies the evidence the scale classifies.
Moment magnitude scale: A logarithmic measure of earthquake size based on seismic moment. It measures the source's overall size, not observed effects at an individual location.
Earthquake early warning system: A system that detects an earthquake and sends alerts before strong shaking reaches some locations. Intensity reports can help assess impacts after warnings and shaking occur.
Modified Mercalli intensity scale (1931): The 1931 revision of the Mercalli intensity scale by Harry O. Wood and Frank Neumann. This revision established the form from which the modern scale developed.
Intensity scale: A system for classifying earthquake effects at locations using ordered descriptive levels. The scale assigns its twelve levels through descriptions of observed effects.
Peak ground acceleration: The maximum acceleration recorded at a site during ground motion. It is an instrumental measurement, unlike the scale's descriptive assessment.

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