How often do earthquakes happen?

 Earthquake Frequency

Earthquakes in the magnitude of one range are called micro quakes. Millions of current around the world every year but they are rarely ever felt.

Magnitude two earthquakes are very minor and are felt slighted by some people but don’t cause any damage. Over a million of these occur every year. These can easily be mistaken for a large vehicle driving nearby.

Earthquakes in the three range are considered minor earthquakes. Around the world over 100,000 of these earthquakes occur every year. They are often felt by people, but very rarely cause any damage. The shaking of objects is most noticeable. The movement could be mistaken for a large construction vehicle operating nearby. The energy released by a low 3-range earthquake is equivalent to a large lightning bolt. 

A light earthquake is in the magnitude 4-range. These earthquakes are more noticeable with the shaking of indoor objects and rattling noises. They are felt by most people in the affected area, but they cause for very little if any damage. It is in this range that most people realize it was an earthquake they felt. The most damage that occurs are usually objects falling off shelves or be knocked over. Around the world 10,000 to 15,000 of these earthquakes occur every year. A high a magnitude four earthquake releases the same energy has an average tornado.

The moderate earthquake category is in the 5 range. 1000 to 1500 of these earthquakes occur around the world every year. These earthquakes cause damage to poorly constructed buildings. Slight or no damage occurs to other buildings, and these earthquakes are felled by everyone in the area.

The magnitude 6 range earthquakes are considered strong earthquakes. The strong earthquakes can cause moderate damage to well-built structures, however earthquake resistant structures have little to moderate damage. These earthquakes are felt throughout much wider area, up to hundreds of miles away from the epicenter. In the epicenter area there is strong to violent shaking. 100 to 150 strong earthquakes occur around the world every year. A low 6-range earthquake releases the same amount of energy has the atomic bomb dropped on Hiroshima.

A major earthquake is in the magnitude 7-range. These earthquakes cause damage to most buildings, with some partially or completely collapsing are receiving severe damage as a result. These earthquakes are felt over significant distances and can cause damage over 100 miles away. Around the world 10 to 20 of these earthquakes occur each year. When Mount St. Helens erupted it released as much energy as a high magnitude 7 earthquake.

Village after 2004 earthquake caused tsunami damage in Sumatra

The magnitude eight and nine earthquakes are considered great. And eight range earthquake will cause major damage to buildings, destroying many structures, and causing moderate to heavy damage to even earthquake resistant buildings. Normally only one magnitude eight range earthquake occurs around the world every year. The world’s largest nuclear test, performed by the Soviet Union, released the energy equivalent of a magnitude 8 earthquake.

On average one magnitude nine or greater earthquake will occur somewhere around the world every 10 to 50 years. Extreme damage and shaking occurs in a very wide area, and near 12 destruction occurs in immediate area. These great earthquakes cause permanent changes to the ground topography.

In the following list,

  • ML refers to Moment Magnitude range
  • Category is how earthquakes in the range are classified
  • MM is the Mercalli Intensity Scale range
  • Average earthquake effects are what you might expect to feel or see, or the damage that can occur.
  • Average frequency is the average number of earthquakes in the range recorded each year.

ML    1.0–1.9
Category    Micro
MM        I
Average earthquake effects: Micro-quakes are rarely felt, but are recorded by seismographs.
Average frequency: Millions / year

ML    2.0–2.9
Category    Micro
MM        I to II
Average earthquake effects: Some people may slightly feel, but no damage occurs to buildings.
Average frequency: 1 million+ / year

ML    3.0–3.9
Category    Minor
MM        III to IV
Average earthquake effects: Most people feel this, but they rarely cause damage. Objects can be seen shaking.
Average frequency: 100,000+ / year

ML    4.0–4.9
Category    Light
MM        IV to VI
Average earthquake effects: Shaking objects and rattling noises are seen and heard. Most people will feel these quakes when indoors, although the shaking is less noticeable outside. Usually causes very little damage to structures. Most damage is caused by objects falling off shelves or being knocked over.
Average frequency: 10,000 to 15,000 / year

ML    5.0–5.9
Category    Moderate
MM        VI to VII
Average earthquake effects: Poorly constructed buildings will receive varying degrees of damage. Little to no damage to other buildings. Everyone in the area feels these quakes.
Average frequency: 1,000 to 1,500 / year

ML    6.0–6.9
Category    Strong
MM        VIII to X
Average earthquake effects: Damage increases to well-built structures, with slight to moderate damage to earthquake-resistance structures. Moderate to severe damage occurs on poorly constructed buildings. In the epicenter area there is strong to violent shaking, and the earthquake can be felt hundreds of miles away.
Average frequency: 100 to 150 / year

ML    7.0–7.9
Category    Major
MM        X to XII
Average earthquake effects: Most buildings will receive at least partial damage, with poorly designed and built structures having severe damage or collapse. 
Average frequency: 10 to 20 / year

ML    8.0–8.9
Category    Great
MM        X to XII
Average earthquake effects: Earthquake-resistant structures may receive moderate to heavy damage. Major damage to other buildings with many likely destroyed. These quakes are felt across large regions.
Average frequency: 1 / year

ML    9.0--
Category    Great
MM        X to XII
Average earthquake effects: Complete or near total destruction. Intense shaking and heavy damage across a large area. Can cause permanent ground topography changes.
Average frequency: 1 every 10 to 50 years


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