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.

Magnitude	Effects
2.0	Felt only nearby, if at all
less than 3.5	Usually not felt
4.0	Often felt up to 10's of kilometers away from the source
3.5-5.4	Often felt, but rarely causes damage
under 6.0	At most slight damage to well-designed buildings. Can cause major damage to poorly constructed buildings over small regions.
6.1-6.9	Can be destructive in areas up to about 100 kilometers across where people live.
7.0-7.9	Major earthquake. Can cause serious damage over larger areas.
8 or greater	Great earthquake. Can cause serious damage in areas several hundred kilometers across
9.0	1952 Kamchatka
9.1	1957 Andreanof Islands, Alaska
9.2	1964 Prince William Sound, Alaska
9.5	1960 Chile - Largest Recorded Earthquake

     2       E
R = ——— log ———
     3       Eo

log E = 1.5ŚR + 4.8   or equivalently:

E = 101.5ŚR + 4.8

Since detonation of 1 ton of TNT releases 4.184Ś10⁹ Joules; we can convert these units to equivalent tons of TNT.

Copyright © 2004, Stephen R. Schmitt