Topic Menu

Cyber-chess a chess instruction site

The Richter Scale

When you hear about an earthquake happening somewhere in the world its magnitude (how big and destructive it is) is usually given on the Richter Scale.

The magnitude value is proportional to the logarithm of the amplitude of the strongest wave during an earthquake.

A recording of 7, for example, indicates a disturbance with ground motion 10 times as large as a recording of 6, and 100 times the recording for a recording of 5.

The energy transferred to the surroundings by an earthquake is affected by the amplitude of the wave. It increases by a factor of 30 for every unit increase in the Richter scale.

The table below gives the frequency of earthquakes and the effects of the earthquakes based on this scale.

Richter scale no. No. of earthquakes per year Typical effects of this magnitude
< 3.4 800 000 Detected only by seismometers
3.5 - 4.2 30 000 Just about noticeable indoors
4.3 - 4.8 4 800 Most people notice them, windows rattle.
4.9 - 5.4 1400 Everyone notices them, dishes may break, open doors swing.
5.5 - 6.1 500 Slight damage to buildings, plaster cracks, bricks fall.
6.2 - 6.9 100 Much damage to buildings: chimneys fall, houses move on foundations.
7.0 - 7.3 15 Serious damage: bridges twist, walls fracture, buildings may collapse.
7.4 - 7.9 4 Great damage, most buildings collapse.
> 8.0 One every 5 to 10 years Total damage, surface waves seen, objects thrown in the air.

 

The effects indicated in the table assume that the earthquake is a shallow earthquake in a populated area. Earthquakes of large magnitude do not necessarily cause the most intense surface effects. The effect in a given region depends to a large degree on local surface and subsurface geologic conditions. An area of unstable ground (sand, clay, or other unconsolidated materials), for example, is likely to experience much more noticeable effects than an area equally distant from an earthquake's epicentre but underlain by firm ground such as granite.

This information was taken from the Matter Project (1999) by Liverpool University