Why do seismic waves travel a curving path through the Earth?
If there were no changes with depth, seismic waves would travel a straight path to the other side of the Earth. But wave arrivals to distant seismic stations have taught us that there are layers. Seismic waves through the Earth follow the same laws of refraction and reflection as any other wave at interfaces. When they encounter boundaries between different media, the wave will react according to Snell’s law, and the angle of refraction across the boundary will depend on the velocity of the second media relative to the first.
- The Earth has boundary changes deep within the earth
- Seismic waves are refracted and reflected at the boundaries and return to the surface
- The boundaries were determined by seismic wave arrivals to distant sttions