Earth & Space
Why do earthquakes happen?
The ground can move suddenly. The Wusels explore movement in Earth's crust.
The short answer
Parts of Earth's solid surface move very slowly. Rock can get stuck and then suddenly slip. The released motion spreads as earthquake waves, making the ground shake.
An imagined Wusel scene
Puschel and Flauschi investigate
At the model, Puschel gently pushes two rough pieces of card past each other. First they stick, then slip. Flauschi marks where the movement became sudden. They record: the model shows slipping, but does not predict a real earthquake.
Try explaining it
Which event can set off earthquake waves?
Choose a), b) or c), then explain your choice.
- a)The plates stay still while only the air above them vibrates.
- b)Stuck rock slips suddenly.
- c)Rock keeps sliding evenly without sticking or suddenly slipping.
Show the explanation
Correct: b): Stuck rock slips suddenly.
Parts of Earth's solid surface move very slowly. Rock can get stuck and then suddenly slip. The released motion spreads as earthquake waves, making the ground shake.
Explore in more detail
Here you will find longer explanations and further details. You can explore them together.
Understand step by step
How it works – simply explained
Rock does not move smoothly everywhere
Plates move slowly. Areas may stick along a fault, a break surface, while continued movement builds stress.
Sudden slip releases energy
When the stuck area gives way, rock regions abruptly slide past each other. Released energy travels as seismic waves.
Waves reach surroundings
They can shake the ground. Effects depend on several conditions. A future earthquake’s precise place and time cannot be reliably predicted.
Why slow movement can cause a sudden jolt
Rock may stick along a fault while surrounding movement slowly builds stress. When the stuck area releases, rock slips. Some released energy travels through rock as waves. Earth does not jump as a whole ball; a local rupture and travelling waves are connected.
The key points again
Discovery 1
Earth’s outer solid layer is divided into moving plates.
Source: [1]
Discovery 2
Rock along faults can stick and then suddenly slip, sending out seismic waves.
Source: [1]
Discovery 3
Many earthquakes happen at plate boundaries, but not all. Their exact time and place cannot be predicted reliably.