Our transcription: Earthquakes aren't the only source of seismic waves.
People sometimes create their own earthshaking devices.
Seismic waves can be generated artificially at the Earth's surface by explosions or by devices which pound on the Earth's surface.
The waves then transfer through the Earth.
This is very similar to X-rays.
For example, when we X-ray a human body, the X-rays, instead of being destructive to the body, are used as a source of energy which can penetrate to the interior of the body and then scatter and reflect off bones or internal organs and then can be documented on a film or some other kind of sensor.
We can then see the interior of the human body.
Similarly, we see the interior of the Earth from the information that comes back from seismic waves.
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