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Monday, December 5, 2011

After the devastating quake on Haiti on January 10/2010, and similar recent large magnitude quakes such as the Indian Ocean in 2004 which triggered a massive tsunami and the recent 2010 Chile quake (8.8 M), it is interesting to see how these events are measured, and what the relative meaning is for the numbers that we hear used (Magnitude, Impact). This posting presents theRichter Scale with its measures and examples.

*List o’ Largest Earthquakes link*

Richter Magnitude Test Scale: Named for Dr. Charles Francis Richter, and developed in 1935. For each whole number jump the impulse (shaking) increases 10-fold, but the energy increases 31.6227769 fold. As an example, an 8.7 magnitude quake generates an amplitude 890.2439024 times greater than a 5.8 quake, but releases an incredible 22,387.2113 times the energy.

Richter MagnitudeApproximate TNT equivalentImpulseExample
0.01 kg (2.2 lb)0.1
0.55.62 kg (12.4 lb).55Large hand grenade
1.032 kg (70 lb)1 (not felt)Construction site blast
1.5177.83 kg (392 lb)5.5WWII conventional bombs
2.01 metric ton10 (very minor, generally not felt)Late WWII conventional bombs
2.55.236 metric tons55WWII blockbuster bomb
3.031.62 metric tons100 (minor, often felt)Massive Ordnance Air Blast bomb
3.5177.83 metric tons550Chernobyl nuclear disaster, 1986
4.01 kiloton1,000 (light, noticeable shaking)Small atomic bomb
4.55.62 kilotons5,500
5.031.62 kilotons10,ooo (moderate, moderate damage)Nagasaki atomic bomb (actual seismic yield was negligible since it detonated in the atmosphere); Lincolnshire earthquake (UK), 2008
5.4125.89 kilotons46,0002008 Chino Hills earthquake (Los Angeles, United States)
5.517883 kilotons55,000Little Skull Mtn. earthquake (NV, USA), 1992; Alum Rock earthquake (CA, USA), 2007
6.01 megaton100,000 (strong, destructive up to 100 miles)Double Spring Flat earthquake (NV, USA), 1994
6.55.62 megatons550,000Rhodes (Greece), 2008; Eureka Earthquake (Humboldt County CA, USA), 2010
6.711.22 megatons730,000Northridge earthquake (CA, USA), 1994
6.922.38 megatons910,000San Francisco Bay Area earthquake (CA, USA), 1989
7.031.62 megatons1 MM (major, destructive up to a few 100 miles)Java earthquake (Indonesia), 2009; 12 January 2010 earthquake (Haiti)
7.144.67 megatons1.9 MMEnergy released is equivalent to that of Tsar Bomba, the largest thermonuclear weapon ever tested.
7.5177.83 megatons5.5 MMKashmir earthquake (Pakistan), 2005; Antofagasta earthquake (Chile), 2007
7.8501.12 megatons8.2 MMTangshan earthquake (China), 1976
8.01 gigaton10 MM (great, destructive up to several 100 miles)Toba eruption 75,000 years ago; the largest known volcanic event; 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 (initial estimate: 7.8)
8.55.62 gigatons55 MMSumatra earthquake (Indonesia), 2007

Vallenar, Chile November 10, 1922

9.031.62 gigatons100MM (rare, destructive up top 1000′s of miles)off the coast of Kamchatka peninsula, Russia November 4, 1952
9.144.67 gigatons190 MMIndian Ocean earthquake, 2004 (40 ZJ in this case
9.263.1 gigatons280 MMAnchorage earthquake (AK, USA), 1964
9.5177.823 gigatons550 MMValdivia earthquake (Chile), 1960
10.01 teraton1 billion (inconceivable global impact)Never recorded
13100 teratons500 ZJYucatán Peninsula impact of asteroid hitting the earth (causingChicxulub crater) 65 M yrs ago.
Source: Richard E.J. Driskill, Electromagnetic Spectrum Authority/ retired

Note that directly the Richter scale is not highly reliable for quakes under 2 or above 8.3 in size. The Richter scale is an open-ended scale. From magnitude 1 through 9, there are roughly 3,341,138 earthquakes each year around the globe.

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