GARY HINCKS / SCIENCE PHOTO LIBRARY GARY HINCKS / SCIENCE PHOTO LIBRARY
Seismic waves. Artwork of the movement of seismic (shock) waves through the Earth from an earthquake's focus beneath the Peruvian Andes (far left). From the focus, shock waves travel through the mantle and core of the Earth. Primary (P) body waves can travel through the core (yellow), but secondary (S) body waves can only travel through the mantle (red). Due to refraction of the waves there is an area (dark, lower right), called the shadow zone, which the waves will not reach. The point on the ground above the focus of the earthquake is called the epicentre. The intensity of the earthquake is shown by isoseismal lines moving outward on the Earth's surface.
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