Why Earthquakes Happen
Explain how sudden movement of rocks underground releases energy that shakes the ground
What a learner can do afterwards
- Explain that earthquakes are caused by rocks underground suddenly moving
- Describe how this movement sends shaking through the surrounding ground
- Distinguish between the underground cause and the surface effects of an earthquake
1 · Read
You know an earthquake makes the ground shake suddenly. Underground rocks may stick while forces keep pushing or pulling them. The rocks slowly bend and store energy. When they suddenly slip along a crack, or break, they release energy. That energy travels through the ground as shaking. A slip can happen along a crack that is already there.
Rocks slip underground near a town. The sudden movement sends energy through the ground. People in the town feel shaking. Another town farther away may feel it too. Shaking usually weakens as it travels farther, though the kind of ground also affects it. The rock movement is the cause. The shaking people feel is an effect.
Ask two questions: What moved underground? What did people feel at the surface?
Earthquakes start when underground rocks suddenly move or break, sending shaking out through the ground around them.
Reading and flashcards written for this learning dataset.
More to read
Before and After a Rock Slip
Earth's outer rocky layer is called the crust. A fault is a crack in rock along which the rocks can move.
Rocks beside a fault may stick while forces keep acting on them. They can slowly bend and store energy. During a sudden slip, some stored energy is released and travels through the ground as earthquake waves.
The fault may have been there long before this earthquake. A fresh crack does not have to form each time rocks slip. People can feel the waves at the surface without a crack opening beside them.
2 · Watch
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