Measuring
the Strength of Earthquakes
When
earthquakes happen, the vibrations in the Earth are recorded
on very sensitive instruments called seismographs. The seismograph
records the movement with zig zag lines. The strength of an
earthquake is measured by looking at the zig zag lines on
the seismograph and measuring their size. A special mathematical
formula is used to convert the size of the lines into a number.
This method was developed by Charles Richter and is known
as the Richter magnitude scale. This scale represents the
strength of an earthquake using a whole number and decimal
fraction (a magnitude 6.3 for example). Each whole number
increase in magnitude represents an increase of 10 times in
the size of the lines recorded by the seismograph. You would
think then that a magnitude 7.3 earthquake would release 10
times more energy than a magnitude 6.3 earthquake. Actually,
because of the nature of the scale, a 7.3 earthquake releases
about 31 times more energy!
Below
is a general description of the relative strength of earthquakes
ranging from a magnitude 1 (not felt) to a magnitude 9 (EXTREMELY
strong). There is not upper limit to the scale (which means
there could be magnitude 10 or more earthquake) but none have
been measured larger than the magnitude 9.5 in Southern Chile
in 1960.
Richter Magnitude Scale
Definitions
| M=1
to 3 |
Usually
not felt but recorded. |
| M=3
to 4 |
No damage,
but often felt. |
| M=5 |
Some damage,
felt a lot. |
| M=6 |
A lot of
damage, old buildings destroyed. |
| M=7 |
Big earthquake
causes serious damage, usually happens in Taiwan, Turkey,
Japan and California. |
| M=8 |
Great earthquake
destroys lots of buildings. Earthquakes felt over an area
of about 1000 km. |
| M=9 |
Dangerous
earthquake, big damage, destroys large region, earthquakes
measures larger than 1000 km. |
