Wednesday, 19 October 2011

The Richter scale - The magnitude of earthquakes

The Richter scale is the best known scale for measuring the magnitude of earthquakes. The magnitude of an earthquake is determined from the logarithm recorded by seismographs. The scale ranges from 0 to 10. Each one-point increase on the scale indicates ten times the amount of shaking and 33 times the amount of energy. For instance an earthquake at Richter scale 6 has a magnitude ten times that at scale 5. Study Fig 4 that shows the magnitude, effects and frequency of earthquakes.

Richter Magnitude
Earthquake Effects
Less than 2.0
Very small earthquakes which are not felt.
2.0 - 2.9
Detected only by seismometers.
3.0 - 3.9
About 49,000 per year
4.0 - 4.9
Everyone notice them e.g. shaking of indoor items, no significant damage.
5.0 - 5.9
Slight damage to well-designed buildings but can cause major damage to poorly constructed buildings.
6.0 - 6.9
Much damage to buildings.
7.0 - 7.9
Can cause serious damage, houses may collapse.
8.0 - 8.9
Cause serious damage, most buildings collapse.
9.0 - 9.9
1 per 20 years
Never recorded