Richter magnitude scale
The Richter magnitude scale, also known as the local magnitude (ML) scale, assigns a
single number to quantify the amount of seismic energy released by an earthquake. It is a
base-10 logarithmic scale obtained by calculating the logarithm of the combined horizontal
amplitude (shaking amplitude) of the largest displacement from zero on a particular type of
seismometer (Wood–Anderson torsion). So, for example, an earthquake that measures 5.0 on
the Richter scale has a shaking amplitude 10 times larger than one that measures 4.0. The
effective limit of measurement for local magnitude ML is about 6.8.Magnitudes are still
widely stated on the Richter scale in the mass media, although usually moment magnitudes—
numerically about the same—are actually given; the Richter scale has been superseded by the
moment magnitude scale, which is calibrated to give generally similar values for mediumsized earthquakes (magnitudes between 3 and 7). Unlike the Richter scale, the moment
magnitude scale is built on sound seismological principles, and does not saturate in the highmagnitude range.
Richter magnitudes
The following describes the typical effects of earthquakes of various magnitudes near the
epicenter. The values are typical only and should be taken with extreme caution, since
intensity and thus ground effects depend not only on the magnitude, but also on the distance
to the epicenter, the depth of the earthquake's focus beneath the epicenter, and geological
conditions (certain terrains can amplify seismic signals).
Richter
Description
magnitudes
Earthquake effects
Less than 2.0 Micro
Microearthquakes, not felt.
2.0-2.9
Generally not felt, but recorded.
Minor
3.0-3.9
Often felt, but rarely causes damage.
4.0-4.9
Light
5.0-5.9
Moderate
6.0-6.9
Strong
7.0-7.9
Major
8.0-8.9
Great
9.0-9.9
10.0+
Epic
Noticeable shaking of indoor items, rattling
noises. Significant damage unlikely.
Can cause major damage to poorly constructed
buildings over small regions. At most slight
damage to well-designed buildings.
Can be destructive in areas up to about 160
kilometres (100 mi) across in populated areas.
Can cause serious damage over larger areas.
Can cause serious damage in areas several
hundred miles across.
Devastating in areas several thousand miles
across.
Never recorded; see below for equivalent
seismic energy yield.
Frequency of
occurrence
About 8,000
per day
About 1,000
per day
49,000 per year
(est.)
6,200 per year
(est.)
800 per year
120 per year
18 per year
1 per year
1 per 20 years
Extremely rare
(Unknown)
Great earthquakes occur once a year, on average. The largest recorded earthquake was the
Great Chilean Earthquake of May 22, 1960 which had a magnitude (MW) of 9.5.[6]
The following table lists the approximate energy equivalents in terms of TNT explosive
force[7] – though note that the energy is that released underground (i.e. a small atomic bomb
blast will not simply cause light shaking of indoor items) rather than the overground energy
release. Most energy from an earthquake is not transmitted to and through the surface;
instead, it dissipates into the crust and other subsurface structures.
Approximate
Richter
TNT for
Joule
Approximate
Seismic Energy equivalent
Magnitude
Yield
0.0
63 kJ
0.5
0.07kg (0.16 oz) .35 MJ
1.0
0.43kg (0.95 lb) 2.0 MJ
1.5
2.42kg (5.34 lb) 11.2 MJ
2.0
30 lb
63 MJ
2.5
168 lb
354 MJ
3.0
952 lb
2.0 GJ
3.5
2.67 metric tons 11.2 GJ
4.0
15 metric tons 63 GJ
4.5
84.2 metric tons 354 GJ
5.0
476 metric tons 2.0 TJ
5.5
2.6 kilotons
11.2 TJ
6.0
15 kilotons
63 TJ
6.5
84 kilotons
354 TJ
6.7
168 kilotons
707 TJ
6.9
333 kilotons
1.4 PJ
7.0
476 kilotons
2.0 PJ
7.1
666 kilotons
2.8 PJ
7.5
2.67 megatons
11.2 PJ
Example
Large hand grenade
Construction site blast
WWII conventional bombs
Late WWII conventional bombs
WWII blockbuster bomb
Massive Ordnance Air Blast bomb
Chernobyl nuclear disaster, 1986
Small atomic bomb
Seismic yield of Nagasaki atomic bomb
(Total yield including air yield 21 kT, 88 TJ)
Lincolnshire earthquake (UK), 2008
Little Skull Mtn. earthquake (NV, USA),
1992
Alum Rock earthquake (CA, USA), 2007
2008 Chino Hills earthquake (Los Angeles,
USA)
Double Spring Flat earthquake (NV, USA),
1994
Caracas (Venezuela), 1967
Rhodes (Greece), 2008
Eureka Earthquake (Humboldt County CA,
USA), 2010
Northridge earthquake (CA, USA), 1994
San Francisco Bay Area earthquake (CA,
USA), 1989
Java earthquake (Indonesia), 2009
2010 Haiti Earthquake
Energy released is equivalent to that of Tsar
Bomba (50 megatons, 210 PJ), the largest
thermonuclear weapon ever tested
1944 San Juan earthquake
Kashmir earthquake (Pakistan), 2005
7.8
7.5 megatons
31.6 PJ
8.0
15 megatons
63 PJ
8.5
84.2 megatons
354 PJ
8.8
238 megatons
1.0 EJ
9.0
476 megatons
2.0 EJ
9.2
9.3
9.5
10.0
947 megatons
1.3 gigatons
2.67 gigatons
15 gigatons
3.98 EJ
5.6 EJ
11.22 EJ
63 EJ
13.0
476 teratons
2.0 YJ
From Wikipedia
Antofagasta earthquake (Chile), 2007
Tangshan earthquake (China), 1976
Hawke's Bay earthquake (New Zealand),
1931)
April 2010 Sumatra earthquake (Indonesia)
San Francisco earthquake (CA, USA), 1906
Queen Charlotte earthquake (BC, Canada),
1949
México City earthquake (Mexico), 1985
Gujarat earthquake (India), 2001
Chincha Alta earthquake (Peru), 2007
Sichuan earthquake (China), 2008
1894 San Juan earthquake
Toba eruption[citation needed] 75,000 years ago;
the largest known volcanic event
Sumatra earthquake (Indonesia), 2007
Chile earthquake, 2010
Lisbon Earthquake (Lisbon, Portugal), All
Saints Day, 1755
Anchorage earthquake (AK, USA), 1964
Indian Ocean earthquake, 2004
Valdivia earthquake (Chile), 1960
Never recorded by humans
Yucatán Peninsula impact (causing
Chicxulub crater) 65 Ma ago (108 megatons =
100 teratons; almost 5x1030 ergs = 500
ZJ).[8][9][10][11][12]