The Mercalli Intensity Scale assigns an intensity or rating to measure the effects of an earthquake at a particular location.

The Mercalli Intensity of any one earthquake can be very different from place to place. This is because the amount of damage caused by an earthquake at a particular location depends on the geology of the location The population density and the methods used to construct buildings near the location are also important in the Mercalli scale.

Although it is an opinionated measure of earthquake size, seismologists still mail questionnaires to local residents after an earthquake asking them to rate the effects of the earthquake at their home.

Earthquake intensities are rated with Roman numerals ranging from I (not felt) to XII (buildings nearly destroyed). This Mercalli scale is from the Loma Prieta earthquake in the Santa Cruz mountains in California.