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Modified Mercalli Scale
The Modified Mercalli Scale (MMS) gives an indication of the intensity of an earthquake while the Richter Scale refers to its magnitude.
The intensity of an earthquake at a particular locality is a measure of the violence of earth motion produced there by the earthquake. It is determined from reported effects of the tremor on human beings, furniture, buildings, geological structure etc. Unlike the magnitude which has a unique value for a particular earthquake, the intensity of an earthquake at a place depends on the distance of that place from the epicentre, the depth of the focus, the intervening and local earth structures and the type of fault motion that caused the earthquake.
Many places, including Hong Kong, have adopted the Modified Mercalli Intensity Scale (MM) which classifies earthquake effects into twelve grades.
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Scale definition |
Picture description |
| Scale I
Not felt except by a very few |
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| Scale II
Felt only by a few persons on upper floors |
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| Scale III
Felt indoors |
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| Scale IV
Hanging objects swing |
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| Scale V
Felt outdoors |
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| Scale VI
Felt by all, many frightened & run outdoors |
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| Scale VII
Difficult to stand |
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| Scale VIII
Damage slight in specially designed structures |
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| Scale IX
Damage considerable in specially designed structures |
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| Scale X
Ground cracked, rail bent |
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| Scale XI
Bridges destroyed, broad fissures in ground |
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| Scale XII
Damage total |
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