To what extent does seismic investigation contribute to our understanding of the Earth's interior structure? Analyze its significance in detail.

Seismic investigation sends P and S-waves to understand Earth's interior structure.

→ It helps in understanding the focus and epicentre of the earthquake.

→ It [?that] wherever the waves travel the fastest, that region is a solid and constitutes earth's crust.

→ Wherever waves travel slowly, that region constitutes mantle as it is semi-solid.

Thus, waves help us determine the depth of the crust and the mantle.