In this post, you’ll read about why and where earthquakes happen. Learn how scientists measure earthquakes and what the “magnitude” of an earthquake actually means and what an “epicenter” is. You’ll discover the connection between earthquakes and the theory of plate tectonics, and learn about the boundary types along which severe earthquakes most commonly occur.
For Teachers: If you’re an educator planning to teach earthquakes or plate boundary movement, great learning resources are key to deepening understanding! I think you and your students will love my complete Plate Tectonics Unit. The information and images in this post come from the unit, and the unit is also packed with diagrams, readings, and activities covering earthquakes, volcanoes, Earth’s layers, boundary types, and more (plus you’ll support my blog with your purchase! ❤️)
What is an earthquake?
An earthquake is ground shaking caused by a sudden release of energy stored within the crust. This energy is supplied by plate tectonic forces. Ground shaking during earthquakes may damage structures, roadways, and other human infrastructure. Earthquakes can also trigger other hazards like tsunamis and landslides.
Where do earthquakes happen?
Earthquakes can happen anywhere different forces are applied on either side of a fault. Earthquakes are most common along plate boundaries. Severe earthquakes occur along transform boundaries and at convergent boundaries with subduction.
Why do earthquakes happen?
We know that earthquakes usually happen at tectonic plate boundaries. But why? It all starts when forces, supplied by tectonic plate movement, are applied to a fault. A fault is a crack or fracture in the bedrock. First, the rocks on either side of the fault must experience different forces. But even when different forces are applied on either side of a fault, the friction between the rocks prevents movement. This causes strain to build.
When the strain becomes too great, it overcomes the friction, and the rocks move rapidly along the fault. This produces ground movement and shaking – what we experience during an earthquake. Think of it like slowly overstretching a rubber band – eventually it will break and rapidly snap back, releasing stored energy. Look at the example below, which shows how forces applied to different sides of faults create an earthquake.
How are earthquakes measured?
The ground movement during an earthquake is caused by seismic waves. Scientists can measure these waves by measuring the ground’s movement up and down or side to side. By measuring seismic waves at different locations, scientists can pinpoint the focus of an earthquake – that is, the exact spot within the ground where the seismic waves are coming from. The epicenter of an earthquake is directly above the focus, on the Earth’s surface.
In addition to finding the location of an earthquake’s focus and epicenter, scientists also measure and compare the size of earthquakes. Often, we rank earthquakes using a number called the magnitude. Lower magnitude earthquakes are common and usually cause minimal damage. Higher magnitude earthquakes are less common but may cause serious damage.
How can we protect ourselves from earthquakes?
In areas at risk of severe earthquakes, people take steps to protect themselves. For example, engineers design buildings that are earthquake-resistant. During an earthquake, the ground under the building rapidly moves back and forth, which makes the building bend and sway. To withstand this, buildings must be made from strong, flexible materials that can bend without breaking or cracking. One good material is steel, but there are other options as well.
Individual people and families can also take measures to protect themselves from earthquakes. Know the earthquake risk in your area. If your area is at risk, make a family earthquake plan for what to do and where to go if an earthquake happens.
Continue Reading…
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There’s no need to scramble to put together the perfect earthquakes lesson – I’ve already created it for you, and you’ll find it within my complete Plate Tectonics Unit! This set includes all the printable materials you need for studying this subject.
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If you enjoyed this post, I know you will love trying my other science and nature units in your classroom too!
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References and Further Reading
- British Geological Survey (n.d.). What causes earthquakes? Available: https://www.bgs.ac.uk/discovering-geology/earth-hazards/earthquakes/what-causes-earthquakes/
- Michigan Tech (n.d.) Why do earthquakes happen? UPSeis. Available: https://www.mtu.edu/geo/community/seismology/learn/earthquake-cause/
- C.C. Plummer, D.H. Carlson, and L. Hammersley (2019). Physical Geology. McGraw-Hill Education. (Chapters 1, 4, 16, and 19)
- Thompson, A. (2023). How to Engineer Buildings That Withstand Earthquakes. Scientific American. Available: https://www.scientificamerican.com/article/how-to-engineer-buildings-that-withstand-earthquakes/