Seismic Wave Behavior: A single boundary refracts & reflects

1min 54s Novice

  • Animation
  • Closed Captioning
Download All 3MB
Optional Files 1

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. 

CLOSED CAPTIONING: .srt file is included with the downloiad. Use appropriate media player to utilize captioning.


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.

Related Animations

Animation shows the race between the direct seismic wave vs. the deeper, longer-path critically refracted seismic wave. Graph records the arrival times.

Animation Novice

Related Lessons

Like other waves, seismic waves obey the laws of physics. In this activity Physics students have the opportunity to apply their understanding of the basic concepts of waves (e.g. reflection, refraction and transmission of energy) as they examine seismic data to determine how far it is from the surface to the bedrock.

Lesson Intermediate