Whenever a major earthquake is in the news, you’ll probably hear about its Richter scale rating. You might also hear about its Mercalli Scale rating, though this isn’t discussed as often. These two ratings describe the power of the earthquake from two different perspectives. The Richter magnitude scale is a scale of numbers used to tell the size of earthquakes. Charles Richter developed the Richter Scale in 1935. His scale was based on theseismogram measured by a particular type of seismometer at a distance of 100 kilometres (62 mi) from the earthquake.
Earthquakes 4.5 or higher on the Richter scale can be measured by tools all over the world.
The scale is logarithmic, with a base of 10. The amplitude of an earthquake that scores 3.0 is about 10 times the amplitude of one that scores 2.0. The energy that is released increases by a factor of about 32.
A majority of quakes register less than 3 on the Richter scale; these tremors, called microquakes, aren’t even felt by humans. Only a tiny portion — 15 or so of the 1.4 million quakes that register above 2.0 — register at 7 or above, which the threshold for a quake being considered major [source: USGS]. The biggest quake in recorded history was the 9.5 quake that struck Chile in 1960. It killed nearly 1,900 people and caused about $4 billion in damage in 2010 dollars [source: USGS]. Generally, you won’t see much damage from earthquakes that register below 4 on the Richter scale.
Richter Magnitude number
Damage caused by the earthquake
Frequency of occurrence
Less than 2.0
Micro (very small) earthquakes, people cannot feel these.
About 8,000 each day
People do not feel these, but seismographs are able to detect them.
About 1,000 per day
People often feel these, but they rarely cause damage.
About 49,000 each year
Objects inside houses are disturbed, causing noise. Nothing is damaged.
About 6,200 each year
Buildings that are not built well may be damaged. Light objects inside a house may be moved.
About 800 per year
Moderately powerful. May cause a lot of damage in a larger area.
About 120 per year
Can damage things seriously over larger areas.
About 18 per year
Massive damage is caused. Heavy objects are thrown into the air and cracks appear on the ground, as well as visible shockwaves. Overhead highways may be destroyed, and buildings are toppled.
About 1 per 20 years
There are no records of anything of this size. The vibration is about the same as that of a 15 mi meteor.
(Adapted from U.S. Geological Survey documents)
The earthquake with the biggest recorded magnitude was the Great Chilean Earthquake. It had a magnitude of 9.5 (approximately 9.5 on the Richter scale) and occurred in 1960. About 6,000 people died because of the earthquake.
Richter ratings only give you a rough idea of the actual impact of an earthquake, though. As we’ve seen, an earthquake’s destructive power varies depending on the composition of the ground in an area and the design and placement of man-made structures. The extent of damage is rated on the Mercalli scale. Mercalli ratings, which are given as Roman numerals, are based on largely subjective interpretations. A low intensity earthquake, one in which only some people feel the vibration and there is no significant property damage, is rated as a II. The highest rating, a XII, is applied to earthquakes in which structures are destroyed, the ground is cracked and other natural disasters, such as landslides or tsunamis, are initiated.
Richter scale ratings are determined soon after an earthquake, once scientists can compare the data from different seismograph stations. Mercalli ratings, on the other hand, can’t be determined until investigators have had time to talk to many eyewitnesses to find out what occurred during the earthquake. Once they have a good idea of the range of damage, they use the Mercalli criteria to decide on an appropriate rating
Approximate Richter Magnitude number
Seismic energy equivalent: Amount of TNT
Large hand grenade
Large Bomb used in WWII
5.6 metric tons
178 metric tons
Chernobyl accident, 1986
Small atomic bomb
2008 Chino Hills earthquake (Los Angeles, United States)
Little Skull Mtn. earthquake (NV, USA), 1992
Double Spring Flat earthquake (NV, USA), 1994
Energy released is equivalent to that of Tsar Bomba, the largest thermonuclear weapon ever tested
Sichuan earthquake (China), 2008 (initial estimate: 7.8)
Indian Ocean earthquake, 2004 (40 ZJ in this case)
108 megatons = 100 teratons
Harris, Tom, and Patrick J. Kiger. “How Earthquakes Work” 16 January 2001. HowStuffWorks.com. <http://science.howstuffworks.com/nature/natural-disasters/earthquake.htm> 03 January 2016.