A seismic wave is the transfer of energy through elastic earth materials by way of particle oscillation/vibration.
![](https://www.geometrics.com/wp-content/themes/geometrics/images/FAQs/seismic_wave+ray.jpg)
A seismic ray, or “wave front normal”, is an arrow drawn perpendicular to the seismic wave front to indicate the propagation direction at that point on the wave front. It is a convenient tool to help understand wave propagation through layered media; it is not something that exists in a physical sense.