medium · Enhanced ACT reading
Seismic P-waves are longitudinal waves that can travel through both solids and liquids, while S-waves are transverse waves that can only travel through solids. When an earthquake occurs, P-waves are detected on the opposite side of the Earth, but S-waves are not.
What does this evidence primarily reveal about the Earth's internal structure?
- S-waves are actually faster than P-waves, but they get reflected back to the surface by the crushing gravity near Earth's very center.
- The Earth contains a liquid layer, such as the outer core, that acts as a barrier to S-waves while allowing P-waves to pass through to the other side.
- The Earth is composed entirely of solid granite, but S-waves lose all of their energy within the first ten kilometers of the Earth's outer crust.
- Earthquakes only produce S-waves when tectonic plates happen to shift horizontally along a fault, which explains why they are missing from some detections.
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