The
European Macroseismic
Scale was introduced in 1998 in order to simplify a description of an
earthquake's effects into a single number.
The sensors for measuring earthquakes are usually based on one (or more) of four groups.
- Living things - people and animals. As intensity increases, a greater proportion of people or animals (a) notice the shaking, and (b) are frightened by it.
- Ordinary objects. As intensity increases, greater numbers of ordinary domestic items (crockery, books, etc) begin to shake and then be upset or thrown down.
- Buildings. As intensity increases, buildings become progressively more severely damaged.
- The natural environment. As intensity increases, there is an increasing likelihood of effects such as cracks in embankments, rockfalls, and so on.
The European Macroseismic Scale is based on three of these four (excluding the natural environment) and is the standard in most European countries for describing the intensity of earthquakes.
The EMS scale was drawn up by a working group ('Macroseismic Scale') of the European Seismological Commission. It took 9 years from the original proposal and over 30 people to draw up the scale (for a full list of contributors see http://www.gfz-potsdam.de/pb5/pb53/projekt/ems/eng/contributors/contrib.htm)
EMS DEFINITION DESCRIPTION
1 Not felt Not felt, even under the most favourable
circumstances.
2 Scarcely felt Vibration is felt only by individual
people at rest in houses, especially on
upper floors of buildings.
3 Weak The vibration is weak and is felt indoors
by a few people. People at rest feel a
swaying or light trembling.
4 Largely observed The earthquake is felt indoors by many
people, outdoors by very few. A few
people are awakened. The level of
vibration is not frightening. Windows,
doors and dishes rattle. Hanging
objects swing.
5 Strong The earthquake is felt indoors by most,
outdoors by few. Many sleeping people
awake. A few run outdoors. Buildings
tremble throughout. Hanging objects
swing considerably. China and glasses
clatter together. The vibration is
strong. Top heavy objects topple over.
Doors and windows swing open or shut.
6 Slightly damaging Felt by most indoors and by many
outdoors. Many people in buildings are
frightened and run outdoors. Small
objects fall. Slight damage to many
ordinary buildings e.g.; fine cracks
in plaster and small pieces of plaster
fall.
7 Damaging Most people are frightened and run
outdoors. Furniture is shifted and
objects fall from shelves in large
numbers. Many ordinary buildings
suffer moderate damage: small cracks
in walls; partial collapse of chimneys.
8 Heavily damaging Furniture may be overturned. Many
ordinary buildings suffer damage:
chimneys fall; large cracks appear in
walls and a few buildings may
partially collapse.
9 Destructive Monuments and columns fall or are
twisted. Many ordinary buildings
partially collapse and a few collapse
completely.
10 Very destructive Many ordinary buildings collapse.
11 Devastating Most ordinary buildings collapse.
12 Completely devastating Practically all structures above and below
ground are heavily damaged or destroyed.
Sources :
http://www.gfz-potsdam.de/pb5/pb53/projekt/ems/eng/index_eng.html
http://www.quakes.bgs.ac.uk
http://www.quakes.bgs.ac.uk/hazard/ems1.htm