What Causes Earthquakes? Discover the Shocking Truth About Earth’s Moving Crust [2025]

The Earth Is Always Changing

The Earth is over 4 billion years old.  That is really, really old!  The Earth is still changing, though.  When volcanoes erupt, land falls apart, or the earth shakes and quakes, we know that things are changing. Huge chunks of rock move under the ground during an earthquake, making the ground shake.  Around the world, earthquakes happen all the time.  A lot of the time, people can't even feel them, but sometimes ones are really big.  These things can do a lot of damage.

How the Earth’s Crust Causes Earthquakes

Earth's crust, which is its top shell, changes when it shakes. The crust is made up of plates, which are groups of about a dozen rocks that are always moving.  They slide past each other, move apart, or crash into each other in different places.  A lot of pressure builds up over time because of this movement.  When the pressure gets too high, the rock chunks move quickly along a fault, which is a crack in the crust.

 Waves: The Energy Behind the Shake

Shock waves are the energy that the moving rocks give off.  The waves went all the way through the rock and caused an earthquake.  People thousands of miles away from the epicenter of the strongest earthquakes can feel the ground shake. A small number of earthquakes are caused by other things, either natural or human.  An earthquake can be caused by the movement of molten rock below a volcano.  Small quakes can be caused by the pressure that builds up when huge dams hold back a lot of water.  Mines and nuclear blasts that happen underground can do the same thing. 

Earth's surface may change when an earthquake is strong enough to push up hills and make huge holes in the ground. A lot of damage can be done to buildings, bridges, railroads, and other things by earthquakes.  Avalanches and other Earth movements are often caused by the strong shaking that happens during earthquakes.  When earthquakes happen in or near the ocean, they can send huge, destructive waves inland. These waves are called tsunamis. 

The Ring of Fire and Global Earthquake Zones

Most earthquakes happen where the edges of the Earth's crustal plates meet.  A big ring of earthquakes goes around the Pacific Ocean and along the hilly west coasts of North and South America. It also goes through Asia's island regions.  The Ring of Fire is what it is called.  Part of this belt is the widely known San Andreas Fault in California.  There is a second, less active belt in the Mediterranean between Europe and North Africa that covers certain areas of Asia.  There are a few quakes that occur inside rocks and not along their edges. 

How Scientists Measure Earthquakes

A seismograph is a tool that scientists use to record the shock waves that an earthquake sends out. There are different ways to figure out how strong an earthquake is.  Earthquakes are ranked on the Richter scale by how much energy they release.  Earthquakes that are very weak are close to zero on the scale, and earthquakes that are very strong are about nine.  On a scale from 1 to 12, the Mercalli scale shows how much damage an earthquake does.