How Is Earthquake Size Measured?
Earthquakes produce seismic waves, or vibrations, that move through the Earth. These waves vary in strength and stronger seismic activity can cause significant damage, sometimes even destroying human settlements or causing tsunamis. In order to study these vibrations, scientists measure their intensity level by utilizing seismographs. Seismographs provide an up and down pattern that indicates seismic activity that occurs in the ground under the equipment. Some of the most advanced seismographs are able to record seismic activity that occurs at any location around the world.
What Is The Richter Scale?
The Richter Scale was developed in 1935 by 2 seismologists, Charles Richter and Beno Gutenberg. The model was based on a previously used scale known as the Mercalli Intensity Scale, although, this instrument was less accurate and based on the observed effects of an earthquake. The creators of the Richter Scale also relied on the apparent magnitude scale, which was used to measure the brightness of stars. It records earthquake intensity by utilizing a base-10 logarithmic formula that measures seismic wave amplitude against an arbitrary amplitude that is measured at a standard distance from the epicenter.
Richter Scale Measurements
The Richter Scale measures earthquakes by using seven different categories: micro, minor, light, moderate, strong, major, and great. Below is a look at each description:
Micro earthquakes are measured at between 1 and 1.9. This magnitude would be considered a I on the Mercalli intensity scale. These earthquakes are not noticed by the general population, although slight movement is recorded by seismographs. Researchers report that this type of seismic activity is constant with several thousand micro earthquakes occurring on an annual basis.
Minor earthquakes are measured at between 2 and 3.9 on the magnitude scale. On the Mercalli intensity scale, this is can be anywhere from a I to a IV. These earthquakes may be felt by some individuals, though not by the majority of the population. They are not known to cause damage to buildings or other infrastructure systems. Researchers report that seismic activity between 2 and 2.9 occurs at a rate of more than 1 million a year. Earthquakes between 3 and 3.9 occur just over 100,000 times a year.
Light earthquakes are measured at between 4 and 4.9 on the magnitude scale, which is anywhere from a IV to a VI on the Mercalli intensity scale. These earthquakes result in noticeable shaking throughout homes and buildings, with objects rattling and sometimes falling off of shelves and walls. Most people can feel this seismic activity, particularly if they are indoors. Some individuals report feeling light earthquakes while outside. These earthquakes do not cause very significant damage. Researchers report that light earthquakes happen between 10,000 and 15,000 times a year.
Moderate earthquakes are measured at between 5 and 5.9. These earthquakes are felt by people both inside and outside of buildings. They are known to cause damage, particularly to weak or poorly built infrastructure. Moderate earthquakes occur between 1,000 and 1,500 times a year.
Strong earthquakes are registered between 6 and 6.9. These earthquakes are known to cause damage to properly constructed buildings, including even those that are considered earthquake resistant. These earthquakes may be felt hundreds of miles from the epicenter, with violent vibrations close to the epicenter. Researchers report strong earthquakes between 100 and 150 times annually.
Major earthquakes are registered between 7 and 7.9. These earthquakes will cause significant damage to the majority of buildings and even collapsing some. Damage from these earthquakes can occur within the 150-mile radius around the epicenter. Researchers report major earthquakes between 10 and 20 times per year.
Great earthquakes are those between 8 and above. These will destroy most buildings and infrastructure systems including roadways and bridges. The shaking and vibrations will cause damage across wide regions. Those above 9.0 have been known to cause topographic changes as well. Earthquakes between 8 and 8.9 happen once a year. Earthquakes at 9 or above happen only once every 10 to 50 years.
Richter Scale Rankings
|Average frequency of occurrence (estimated)
|Continual/several million per year
|I to II
|Over one million per year
|III to IV
|Over 100,000 per year
|IV to VI
|10,000 to 15,000 per year
|VI to VIII
|1,000 to 1,500 per year
|VII to X
|100 to 150 per year
|VIII or greater
|10 to 20 per year
|VIII or greater
|One per year
|9.0 and greater
|VIII or greater
|One per 10 to 50 years