Can anyone explain why seismic waves travel through the earth on curved paths?
I will try to explain this in simple terms, but I can expand the answer if you request me to. The seismic velocity of the Earth generally increases with depth, so for this explanation I will consider a laterally homogeneous Earth that has layers of increasing velocity as depth increases. For a raypath of a downward going wavefront from a point source leaving a angle a1 through a layer with velocity v1, we can calculate the ray parameter, p, as p=sin(a1)/v1. Ray parameter is a constant. Now the wavefront encounters a layer of higher velocity, v2. Since p is constant, p= sin(a1)/v1=sin(a2)/v2; this means that for a down going wave a2 must be greater than a1. When a2=90 degrees the wavefront will be traveling horizontally before it travels back up to the Earth’s surface. |\ | \ v1 | \ |a1\ | \ <--raypath ____\_________________________________… | \ v2 layer2 | \ | a2 \ | \ Raypaths curve in the Earth due to the increase of velocity with depth. For more detailed information you can look up
