As you may have noticed, the Japanese don't generally use the same scale as you may be used to to measure earthquake intensity. Instead of the level of magnitude which we use in the West, they have a system called 震度 "shindo". The main difference is that this scale measures the physical shaking of the surface of the earth at numerous points. This is why the earthquake report maps look like the one to the right (incidentally taken from yesterday's quake), where there is a strength gradient across affected areas.

For a visual representation of what this means, the Japanese Meteorological Agency has this useful graphic (click to enlarge):




And here it is in text:



JMA Seismic Intensity Scale
0
Nobody feels the tremor.
1
Some people indoors may feel a slight tremor.
2
Many people indoors feel the tremor. Hanging fixtures, such as lights, may slightly shake.
3
Most people indoors feel the tremor. Electrical wires may slightly shake.
4
Hanging fixtures shake considerably and dishes in the cupboard may rattle.
Lower 5
Many people feel the need to plan for safety. Dishes in the cupboard and books in the shelves may fall. Items that are not supported well may fall.
Upper 5
There is a sense of extreme danger. Heavy furniture, such as bureaus, may fall over. Many brick walls that are not supported well may topple.
Lower 6
People cannot maintain a standing position. Furniture that is not secured may move or topple over. Many doors will not open. Window glass of buildings will break and fall down.
Upper 6
Impossible to move without crawling. Furniture that is not secured may move or topple over. Most brick walls that are not supported well ill fall.
7
Unable to move or act by will. Most furniture will move, and some may seem to fly.


More detailed information about the effect on buildings etc can be found on the JMA site.

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