Resource Library

ENCYCLOPEDIC ENTRY

ENCYCLOPEDIC ENTRY

Earthquakes

Earthquakes

Earthquakes happen everyday around the world. Often, people can’t feel them, but sometimes they cause great devastation.

Grades

5 - 8

Subjects

Earth Science, Geology

Image

Woman Awaiting Aid after Earthquake

While most earthquakes are barely noticeable, others can be devastating. Major earthquakes—magnitude 7.0-7.9—and great earthquakes—magnitude of 8.0 or higher—can destroy buildings and kill people and other animals.

Photograph by ARKO DATTA/AFP

Hundreds of earthquakes occur on Earth everyday. Most of them are small, barely detectable by most people. But occasionally there is a much more significant quake. On average, a major earthquake—one with a magnitude of 7.0-7.9—strikes somewhere on the planet more than once a month. A great earthquake—with a magnitude of 8.0 or higher—occurs about once a year.

An earthquake can happen anywhere. However, the vast majority of earthquakes occur at the boundaries between tectonic plates. Continental and oceanic plates may move toward each other, scrape past each other, or pull apart as they move slowly across the planet's upper mantle. This movement of the plates, and the pressure that is built up at the boundaries, can result in earthquakes.

The boundaries between plates contains systems of deep cracks, called faults. Most earthquakes occur along these faults. Within a fault, rock masses on either side of the break are pushed by geologic forces in opposite directions. Friction, however, holds the rocks in place, causing stresses to build. Finally, the mounting pressure overcomes the friction and a sudden movement occurs along the fault, releasing a large amount of energy. This is an earthquake.

While the vast majority of earthquakes occur along faults at Earth's plate boundaries, occasionally, a quake occurs in the middle of a plate, far from any boundary. Such quakes make up less than 10 percent of all earthquakes. While these intraplate quakes are not completely understood, scientists theorize that they may result from weaknesses within Earth’s crust from long ago. Although rare and not well understood, these earthquakes are no less devastating than those that occur along plate boundaries. Earthquakes along the New Madrid Fault, along the Mississippi River in the United States, in 1811–1812 were among the strongest quakes ever recorded. More recently, in 2001, an intraplate earthquake in the Gujarat region of northwesternn India killed more than 20,000 people.

Believe it or not, earthquakes aren’t just Earth-bound phenomena. Astronauts who traveled to the moon in the late 1960s and early 1970s installed seismographs, devices used to measure and record vibrations, on the lunar surface. The data radioed back to Earth showed that “moonquakes” occur and can be fairly strong and last much longer than quakes on Earth!

Media Credits

The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit. The Rights Holder for media is the person or group credited.

Director
Tyson Brown, National Geographic Society
Author
National Geographic Society, National Geographic Society
Production Managers
Gina Borgia, National Geographic Society
Jeanna Sullivan, National Geographic Society
Program Specialists
Sarah Appleton, National Geographic Society, National Geographic Society
Margot Willis, National Geographic Society
Producer
Clint Parks,
other
Last Updated

May 20, 2022

For information on user permissions, please read our Terms of Service. If you have questions about licensing content on this page, please contact ngimagecollection@natgeo.com for more information and to obtain a license. If you have questions about how to cite anything on our website in your project or classroom presentation, please contact your teacher. She or he will best know the preferred format. When you reach out to him or her, you will need the page title, URL, and the date you accessed the resource.

Media

If a media asset is downloadable, a download button appears in the corner of the media viewer. If no button appears, you cannot download or save the media.

Text

Text on this page is printable and can be used according to our Terms of Service.

Interactives

Any interactives on this page can only be played while you are visiting our website. You cannot download interactives.

Related Resources