The Richter scale is a logarithmic scale used to measure the destructive
power of an earthquake. It was devised by Charles F. Richter in
1935 for measurement of the strength of local earthquakes in southern
California. It is a measure of the amplitude of the seismic waves
produced by an earthquake. An increase of one unit on the Richter
scale, say from magnitude 2.4 to 3.4, corresponds to a 10-fold increase
in the amplitude of the seismic waves that shake the ground. The
Richter magnitude is also related to the energy radiated from the
earthquake source as seismic waves. An increase of one unit corresponds
to approximately a 30-fold increase in the total energy released.
Some of the effects we may observe are tabulated below.
|Felt only nearby, if at all
|less than 3.5
|Usually not felt
|Often felt up to 10's of kilometers
away from the source
|Often felt, but rarely
|At most slight damage to well-designed
buildings. Can cause major damage to poorly constructed buildings
over small regions.
|Can be destructive in areas up
to about 100 kilometers across where people live.
|Major earthquake. Can cause serious
damage over larger areas.
|8 or greater
|Great earthquake. Can cause serious
damage in areas several hundred kilometers across
|1957 Andreanof Islands, Alaska
|1964 Prince William Sound, Alaska
|1960 Chile - Largest Recorded Earthquake