Japan Meteorological Agency seismic intensity scale

The Japan Meteorological Agency (JMA) Seismic Intensity Scale (known in Japan as the Shindo seismic scale) is a seismic intensity scale used in Japan to categorize the intensity of local ground shaking caused by earthquakes.

The JMA intensity scale differs from magnitude measurements like the moment magnitude (Mw ) and the earlier Richter scales, which represent how much energy an earthquake releases. Similar to the Mercalli scale, the JMA scale measures the intensities of ground shaking at various observation points within the affected area. Intensities are expressed as numerical values called shindo (震度, "seismic intensity"); the higher the value, the more intense the shaking. Values are derived from ground acceleration and duration of the shaking, which are themselves influenced by factors such as distance to and depth of the hypocenter (focus), local soil conditions, and nature of the geology in between, as well as the event's magnitude; every quake thus entails numerous intensities.

Intensity data is collected from 4,400 observation stations equipped with "Model 95 seismic intensity meters" that measure strong ground motion. The agency provides authorities and the general public with real-time reports through the media and Internet giving event time, epicenter (location), magnitude, and depth followed by intensity readings at affected localities.

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