The Richter Scale is used by scientists to measure the
magnitude of earthquakes. It was developed by an American
seismologist Charles Richter in 1935.
The seismic ways of an earthquake that is a 6.0 on the scale
are 10 times the amplitude of an earthquake that measures 5.0 on the
scale. In terms of energy released a 6.0
earthquake releases 32 times more energy than a 5.0
earthquake. Since every increase of one on the
Richter scale has an increased amplitude of 10, the
Richter scale is a logarithmic scale rather than a linear one. Earthquakes
that are under two on the richter scale are barely felt on
the surface. About 8 000 of these occur in the world
every day. Earthquakes between 2.0 and 2.9 are
minor earthquakes, but are not really felt but are recorded
by seismographs. There are around 1 000 earthquakes like
this every day around the world. Earthquakes between 3.0
and 3.9 on the Richter scale are often felt
but do little damage globally. There are an estimated 49 000 earthquakes like
this a year. Earthquakes between 4.0 and 4.9 on the
Richter scale are considered to be light earthquakes.
They will shake things that are indoors but not cause much damage.
There are about 6200 earthquakes like this a year.
Earthquakes between 5.0 and 5.9 are considered moderate.
If a building is poorly constructed an earthquake like this can cause
significant damage. But they make little impact on modern
earthquake-proof buildings. There are about 800
earthquakes a year of this magnitude. Earthquakes between 6.0 and 6.9 are
considered to be strong earthquakes These can be very destructive over a
large area. There are around 120 earthquakes of this
magnitude globally every year. Earthquakes between 7.0 and 7.9 on the Richter
scale are considered major quakes. These can cause serious damage over even
large areas. There are about 18 earthquakes of this magnitude
globally every year. Earthquakes between 8.0 and 8.9 on the Richter scale are
considered great earthquakes. Earthquakes of this magnitude can cause
serious damage over several hundred kilometres.
Generally there is one earthquake of this magnitude every year.
For example the devastating Sichuan earthquake of May 12th 2008
had a magnitude of 8.0 and killed 87 000 people.
Earthquakes between 9.0 and 9.9 on the Richter
scale can devastate regions for thousands of kilometers.
Generally there is an earthquake of this magnitude once
every 20 years, but in the early 21st century
the world has twice been shaken by earthquakes of this magnitude.
On boxing day 26 December 2004 a 9.3 magnitude earthquake at a depth of
30 kilometres off the west coast of northern Sumatra
generated tsunami waves between 15 and 30 meters.
The resulting wave traveled across the Indian Ocean
causing over 227 000 deaths and enormous destruction across many countries.
On February 2012 a 9.1 magnitude
earthquake of Japan's Pacific coast at a depth of 29 kilometres also
generated a massive tsunami that resulted in over 20 thousand people
dead or missing. Earthquakes at 10.0 or above scale
have never been recorded by living people. However
such an earthquake of this size may theoretically be caused by a massive
asteroid strike - an extinction level event.
It must be noted that the magnitude of an earthquake is not the only factor in
determining how devastating it is felt on the surface.
The depth of where an earthquake takes place in the proximity of the
earthquake's focus to populated areas has a significant
bearing on how much damage it will do. Earthquakes at depths less than 70
kilometres from the surface are considered shallow earthquakes.
Earthquakes with an epicenter between 70 to 300 kilometres are considered to have
an intermediate depth, and earthquakes with an epicenter over
300 kilometres below the surface are considered to be deep earthquakes.
The Christchurch earthquake of 22nd February 2011 was 6.3 on the Richter
scale and did far more damage to life and
property than the larger Darfield earthquake of 4th
September 2010, which measured a 7.1.
The reason for this was the geographic proximity of the aftershock's epicenter to Christchurch.
The Christchurch quake was just five kilometres deep
and directly below the Heathcote valley, a suburb of Christchurch.
The Darfield quake was 40 kilometres
west of Christchurch and 10 kilometres deep.
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