What happens when seismic waves hit a boundary between faster and slower layers?
This introduction to seismic wave behavior describes Snell's Law and how it applies to layers in the earth. It addresses reflected, refracted, critically refracted, and head waves. And ends with a quiz about which path is the fastest to seismic stations 30-100 meters away. Seismic waves travel at different speeds through different materials. In this 2-layer model two wave fronts leave an impact at the same time but the lower layer is faster.
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Snells Law describes how seismic ray paths bend as they travel from one material into another.
- They bend toward vertical when going from fast to slow; and
- bend toward horizontal when going from a slower to a faster material.
- When the rays are refracted 90 degrees from normal, they travel along the boundary in the fast layer.