What scale measures the intensity of earthquake shaking?

The Mercalli scale measures the intensity of earthquake shaking. More precisely, the modern version commonly used in the United States is the Modified Mercalli intensity scale, which records the observed effects of an earthquake at a particular location.

Unlike a magnitude scale, Mercalli intensity can vary from place to place during the same earthquake. It is based on what people feel and what happens to buildings, objects, and the ground. Intensity I means the earthquake is generally not felt, while the highest categories describe extreme damage and major ground effects.

Local conditions strongly influence the result. Distance from the epicentre, earthquake depth, soil type, building design, and the direction of energy release can all change the shaking experienced by a community. Soft sediments, for example, may amplify motion compared with solid bedrock.

The main mix-up is with the Richter or moment magnitude scales. Magnitude describes the earthquake’s overall size at its source; Mercalli describes its effects at a specific site. Giuseppe Mercalli developed an early ten-degree scale in 1902, and later revisions produced the twelve-level Modified Mercalli system.