Question

How do seismic waves provide evidence for the earth's structure?

Answer 1

Here's a couple of good previous answers on Socratic:
https://socratic.org/questions/how-are-seismic-waves-used-to-determine-the-structure-of-the-earth

https://socratic.org/questions/how-do-seismic-waves-reveal-the-structure-of-earth-s-interior