GARY HINCKS / SCIENCE PHOTO LIBRARY GARY HINCKS / SCIENCE PHOTO LIBRARY
Secondary seismic waves. Artwork showing the form of secondary (S) seismic (shock) waves during an earthquake. An earthquake is caused by the sudden movement of rocks in the Earth's crust. The initial tremor of an earthquake can be likened to shaking a piece of rope up and down. This sets up transverse waves within the rope, which oscillate up and down at right angles to the direction of travel (arrowed). S waves travelling through a body of rock cause it to shear. S waves arrive at the surface after the faster primary (P) waves. S waves can travel through the solid crust and mantle of the Earth, but not through its liquid core. See E360/009 for a diagram of P waves.
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