Magnitude and intensity quick reference

Quick reference

Magnitude and intensity are different measurements with frequently confused values. Magnitude (Richter ML, moment magnitude Mw) is a property of the earthquake as a whole — there is one number per event. Intensity (Modified Mercalli, MMI) is a property of how the earthquake felt and what it damaged at a particular location — there are many MMI values for any one earthquake, varying with distance, soil conditions, and building stock. The values below are summarized from the Modified Mercalli intensity scale article, supplemented by USGS and Wikipedia descriptions of the moment-magnitude framework. The intensity-to-felt-effects mapping is approximate; local geology, building type, and depth of the earthquake all modify the relationship.