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Richter scale
Richter scale
The system used to measure the energy in an earthquake (see: Table right). Developed by Charles Richter, an American, in 1935.
(See also: Magnitude and Modified Mercalli scale.)
Rift, rift valley
A large trench in the crust usually caused by tension. Rift valleys
are common where the crust is spreading. Parallel normal faults allow some blocks to sink between others and form valleys. Volcanoes often form as magma rises up along fault lines. The East African Rift Valley is the world’s largest continental rift valley. (See also: Rifting.)
Rifting
The process of crustal stretching that causes blocks of crust to sink, creating rift valleys.
Ring of Fire
(See: Pacific Ring of Fire.)
Rock
The solid material on the Earth’s surface. Rocks are classified into igneous (formed from magma), metamorphic (formed by great
heat and pressure), and sedimentary (formed as layers laid down mostly on ocean floors). (See also: Erosion.)
Horst
Horst
 Rift valley – As the crust is broken by pressure or tension along parallel lines, slabs of rock can rise or fall to create rift valleys (graben) or block mountains (horsts).
The Richter scale
This is a scale for measuring the intensity of an earthquake. It was developed by American scientist Dr Charles F. Richter. It is a measure of the energy released by an earthquake.
The Richter scale is not an even scale. Each unit on it is ten times bigger than the one below it. This allows a huge range of values to be placed on one scale.
Earthquake magnitudes are not very closely connected to the effect of the earthquake. The effect depends on the kind of rock in which the earthquake occurred.
Magnitudes
Less than 3.5 3.5–5.4 5.5–6.0
6.1–6.9 7.0–7.9 8+
Effects
Generally not felt, but recorded. Often felt, but rarely causes damage.
Can cause major damage to poorly constructed buildings; has little effect on well-constructed buildings.
Can be destructive in areas up to about 50 kilometres from the focus. Major earthquake. Can cause serious damage over larger areas.
Great earthquake. Can cause serious damage in areas more than 100 kilometres from the focus.
The table below describes the energy in an earthquake in terms of an equivalent amount of TNT explosive (after USGS).
Richter TNT for seismic
scale magnitude
-1.5 18 grams
1.0 15 kilogrammes 1.5 150 kilogrammes 2.0 1 tonne
2.5 4.6 tonnes
3.0 29 tonnes
3.5 73 tonnes
4.0 1,000 tonnes
4.5 5,100 tonnes
5.0 32,000 tonnes 5.5 80,000 tonnes 6.0 1 million tonnes 6.5 5 million tonnes 7.0 32 million tonnes
7.5 160 million tonnes 8.0 1 billion tonnes 8.5 5 billion tonnes 9.0 32 billion tonnes
10.0 1 trillion tonnes 12.0 160 trillion tonnes
Example
Energy yield (approximate)
Breaking a rock on a lab table Large blast at a construction site
Large quarry or mine blast
Small nuclear weapon Average tornado (total energy)
Little Skull Mtn., NV, Quake, 1992 Double Spring Flat, NV, Quake, 1994 Northridge, CA, Quake, 1994 Hyogo-Ken Nanbu, Japan, Quake, 1995; Largest thermonuclear weapon Landers, CA, Quake, 1992
San Francisco, CA, Quake, 1906 Anchorage, AK, Quake, 1964
Chilean Quake, 1960
(San Andreas type fault circling Earth) (Sunlight received by the Earth every day)
Graben
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