Earthquake
Magnitude - John Seach
Magnitude is measure of the strength
of an earthquake or strain energy released by it, as determined by seismographic
observations. This is a logarithmic value originally defined by Charles
Richter (1935). An increase of one unit of magnitude (for example, from
4.6 to 5.6) represents a 10-fold increase in wave amplitude on a seismogram
or approximately a 30-fold increase in the energy released. In other words,
a magnitude 6.7 earthquake releases over 900 times (30 times 30) the energy
of a 4.7 earthquake - or it takes about 900 magnitude 4.7 earthquakes to
equal the energy released in a single 6.7 earthquake! There is no beginning
nor end to this scale. However, rock mechanics seems to preclude earthquakes
smaller than about -1 or larger than about 9.5. A magnitude -1.0 event
release about 900 times less energy than a magnitude 1.0 quake. Except
in special circumstances, earthquakes below magnitude 2.5 are not generally
felt by humans.
Magnitude
(Richter Scale)
|
Effects
|
Number per year
|
|
less than 2
|
Not felt by
humans. Recorded by instruments only. |
Numerous
|
|
2-3
|
Felt only
by the most sensitive. Suspended objects swing |
300,000
|
|
3-4
|
Felt by some
people. Vibration like a passing heavy vehicle |
49,000
|
|
4-5
|
Felt by most
people. Hanging objects swing. Dishes and windows rattle and may break |
6,200
|
|
5-6
|
Felt by all;
people frightened. Chimneys topple; furniture moves |
800
|
|
6-7
|
Some panic.
Buildings may suffer substantial damage |
120
|
|
7-8
|
Widespread
panic. Few buildings remain standing. Large landslides; fissures in ground |
18
|
|
8-9
|
Complete devastation.
Ground waves |
1 every few years
|
    
Earthquake Magnitude
www.volcanolive.com
Copyright John Seach
|