How Do We Know about Layers Deep within Earth?
ES0402  Locating Layers
Jennifer Loomis, TERC
Here is a model that contains more than one layer. Recall that P waves move through both solids and liquids, but S waves can’t move through liquids.

  !   Click the image to begin the animation. Click and drag the slider back and forth to help you analyze the wave patterns.

6. Observe the path taken by P and S waves in the model planet. Sketch the layers on your diagram and indicate if they are solid or liquid.

Notice how the P and S waves break apart when they hit the central layer, or core, of the model. In a similar manner, Earth's core affects P and S waves' paths on their way through the planet. Consequently, some areas on the side of Earth opposite from the earthquake do not receive P or S waves. The area where P and S waves do not arrive is called the shadow zone.

  !   Play the animation again. Examine the frames near the end of the animation to identify the areas where no P or S waves are received. Try to visualize the doughnut-shaped area of the shadow zone on Earth’s surface.


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