Skip links

Earthquakes Causes, Effects and Facts For Kids


In order to understand what earthquakes are, it is important to first understand that the Earth is constructed in a sphere made up of concentric layers. Beginning from the innermost layer of the planet, the inner core, the earth is wrapped in the outer core, the mantle, upper mantle and finally, the crust. It is within the crust, the thinnest layer that the root of earthquakes rests.

The earth’s topmost layer contains what are called tectonic plates. Some plates are quite large, covering entire continents and oceans, while others are very small, covering only one country in the Middle East or one part of the Pacific Ocean. From largest to smallest, the main tectonic plates include the Pacific Plate (at 103 million square kilometers), the African Plate (at 78 million square kilometers), the North American Plate (at 76 million square kilometers), the Eurasian Plate (at 68 million square kilometers), the Antarctic Plate (at 61 million square kilometers), the Indo-Australian Plate (at 47 million square kilometers) and the South American Plate (at 44 million square kilometers).

The lines along which the boundaries of the tectonic plates meet can be classified into three categories. The first is called a Convergent boundary. At this joint, two plates are pushed together against one another, resulting in the formation of a ridge–like mountain. Alternately, when two plates are pushed against each other at a Convergent boundary, one plate can slide underneath the other plate, destroying the earth below, but avoiding the formation of any mountains. A Divergent boundary is one in which the two tectonic plates are pulled away from each other, leaving a crack or crevice in the Earth’s layers. Transform boundaries are those meeting points in which tectonic plates slide against each other, neither pushing against and pulling away from the other.

Originally, it was not known why earthquakes occurred, although they have been recorded throughout history for thousands of years. In 1871, a Japanese geologist, Bunjiro Koto, first began to study why these natural disasters took place. He was the first scientist on record who believed that earthquakes were caused by fault lines in the Earth’s crust. In 1906, San Francisco experienced a horrific earthquake. Henry Reid studied the quake and, in conjunction with Koto’s idea, explained earthquakes as energy being released as a result of strain that causes a fault line to rupture.

2. Can earthquakes be predicted?

Earthquakes are unable to be predicted. Scientists have tried for more than 100 years to discover ways to work out the exact science behind figuring out when these natural disasters will happen, but as of yet, remain unsuccessful.

3. Where did the 10 largest earthquakes take place during the 20th and 21st centuries (magnitudes below in parentheses)?

1. Chile (9.5)
When was the Chile Earthquake: May 22, 1960

2. Prince William Sound, Alaska (9.2)
When was the Prince William Sound Earthquake: March, 28, 1964

3. Andreanof Islands, Aleutian Islands (9.1)
When was the Andreanof Islands Earthquake: March 9, 1957

4. Kamchatka, Russia (9.0)
When was the Kamchatka Earthquake: November 4, 1952

5. Sumatra, Indonesia (9.0)
When was the Sumatra Earthquake: December 26, 2004

6. Ecuador (8.8)
When was the Ecuador Earthquake: January 31, 1906

7. Maule, Chile (8.8)
When was the Maule Earthquake: February 27, 2010

8. Rat Islands, Aleutian Islands (8.7)
When was the Rat Islands Earthquake: February 4, 1965

9. Northern Sumatra, Indonesia (8.7)
When was the Northern Sumatra Earthquake: March 28, 2005

10. Border of India and China (8.6)
When was the Earthquake: August 15, 1950

4. How are earthquakes measured?

Earthquakes are measured with the use of a seismograph, a device that scientifically records the magnitude of the shaking. A basic seismograph suspends a pen attached to a weight, attached to a solid base. When the base is ruptured as a result of an earthquake, the pen begins to draw squiggly lines of varying size on a piece of paper that scrolls along where the pen is hanging. The varying size of the resulting squiggle determines the magnitude of an earthquake.

In 1935, Charles Richter thought that there was a need to develop a scale to measure the readings of a seismograph, thus allowing further study of large quakes versus smaller tremors. The scale is based on a loose range of 0-10. Earthquakes measuring less than 2 on the Richter scale are called microearthquakes, and cannot even be felt by humans. These are very common, occurring up to 10,000 times per day all over the world. Earthquakes measuring between 2.0 and 3.9 on the Richter scale can be felt by humans, but are not alarming enough to be recorded or cause any damage. These tremors occur around 100 to 1000 times daily. Light earthquakes measure between 4.0 and 4.9, and are felt quite distinctly. Rattling items within buildings can be heard, but often there is no significant damage. These are still quite common, at over 6,000 annually. Moderate earthquakes measure between 5.0 and 5.9 on the Richter Scale and can cause major damage in poorly developed areas with unstable buildings. These happen almost 1,000 times annually, or around 3 times per day. Strong earthquakes measure between 6.0 and 6.9 on the Richter scale and happen around once every 3 days, or 120 times per year. Major earthquakes are extremely destructive, and measure between 7.0 and 7.9 on the scale. Great earthquakes measure between 8.0 and 9.9 on the scale. Those in the 8 range happen around one time annually, while those reaching into the 9 range happen only once every decade or two.

5. How long do earthquakes last?

Earthquakes, although they have no set length, typically last between a few seconds and around 30 seconds. Aftershock earthquakes can occur after the first original quake, but these are recorded as separate occurrences.

6. Different Levels of Earthquakes

Instrumental
Richter Magnitude <2
Mercalli Intensity I
Moment Magnitude 1.0 – 3.0
TNT Equivalent < 1 ton
Frequency of Occurence About 8,000 per day
Actual Observation of the Earthquake Microearthquakes, usually not felt – detected by instruments

Feeble 
Richter Magnitude 2
Mercalli Intensity II
Moment Magnitude 3.9
TNT Equivalent 1 ton
Frequency of Occurence About 1,000 per day
Actual Observation of the Earthquake Often felt, especially on upper floors – detected by instruments

Slight 
Richter Magnitude 3
Mercalli Intensity III
Moment Magnitude 4
TNT Equivalent 29 tons
Frequency of Occurence 49,000 per year
Actual Observation of the EarthquakeFelt noticeably indoors, vibration like passing vehicles, cars may rock

Moderate
Richter Magnitude 4-Mar
Mercalli Intensity IV
Moment Magnitude 4.9
TNT Equivalent 73 tons
Frequency of Occurence 49,000 per year
Actual Observation of the Earthquake Felt indoors by many, felt outdoors by few. Dishes and doors disturbed, like a heavy truck nearby, walls-cracking sound

Rather Strong
Richter Magnitude 4
Mercalli Intensity V
Moment Magnitude 5
TNT Equivalent 1 kiloton
Frequency of Occurence 6,200 per year
Actual Observation of the Earthquake Felt by most people, slight damage. Some dishes and windows broken, some cracked plaster, trees disturbed

Strong 
Richter Magnitude 5
Mercalli Intensity VI
Moment Magnitude 5.9
TNT Equivalent 5.1 kilotons
Frequency of Occurence 800 per year
Actual Observation of the Earthquake Felt by all, many frightened and run outdoors. Damage minor to moderate

Very Strong
Richter Magnitude 6-May
Mercalli Intensity VII
Moment Magnitude 6
TNT Equivalent 80 kilotons
Frequency of Occurence 800 per year
Actual Observation of the Earthquake Everyone runs outdoors. Much damage to poor designed buildings, some chimneys broken, noticed by people driving cars

Destructive
Richter Magnitude 6
Mercalli Intensity VIII
Moment Magnitude 6.9
TNT Equivalent 1 megaton
Frequency of Occurence 120 per year
Actual Observation of the Earthquake Everyone runs outdoors. Damage moderate to major. Minor damage to well designed structures, major damage in poor designed structures. Chimneys, columns and walls falls. Heavy furniture turned. Well water changes, sand and mud ejected

Ruinous 
Richter Magnitude 7
Mercalli Intensity IX
Moment Magnitude 7
TNT Equivalent 32 megatons
Frequency of Occurence 18 per year
Actual Observation of the Earthquake Can cause serious damage over larger areas. Major damage in all structures, ground cracked, pipes broken, shift foundation

Disastrous
Richter Magnitude 8-Jul
Mercalli Intensity X
Moment Magnitude
TNT Equivalent 160 megatons
Frequency of Occurence 18 per year
Actual Observation of the Earthquake Major damage, most masonry and frame structures destroyed. Ground badly cracked, landslides, water sloshed over river banks, rails bent

Very Disastrous
Richter Magnitude 8
Mercalli Intensity XI
Moment Magnitude
TNT Equivalent 1 gigaton
Frequency of Occurence 1 per year
Actual Observation of the Earthquake Almost all masonry structures destroyed, bridges fall, big fissures in ground, land slumps, rails bent greatly

Catastrophic
Richter Magnitude >8
Mercalli Intensity XII
Moment Magnitude
TNT Equivalent >1 gigaton
Frequency of Occurence 1 per 20 years
Actual Observation of the Earthquake Devastating in areas several thousand miles across. Total destruction, Ground surface waves seen, objects thrown in the air. All constructions destroyed.

Earthquake resources and lesson plans

US Geological Survey – Earthquake Topics and Lessons website

Earthquake Classroom Activities and Lesson Plans website

Quick trivia for kids about earthquakes

Where and when was the greatest earthquake in American history?

The largest earthquake in American history was the Great Alaskan Earthquake of 1964. The quake, on March 28, 1964, had its epicenter near Anchorage and measured a 9.2 on the Richter scale. This is the second highest magnitude ever recorded, behind a 9.5 earthquake in Chile.