Compare and contrast primary (P) and secondary (S) waves. How are they used to determine the nature of the land?

We know the speeds they travel through different rocks from lab experiments, so we can infer from their arrival times—and often from the difference in arrival times or S minus P time—what types of rocks they have traveled through to move from source to detector. P waves are longitudinal or compression waves that oscillate in the direction of their motion (like a worm). S waves are transverse waves that oscillate perpendicular to their direction of travel (like a snake).

Primary (P) waves are compressional waves that travel through solids and liquids, while secondary (S) waves are shear waves that only travel through solids. P waves are faster than S waves. Seismic waves help determine the Earth's interior composition and detect subsurface structures, revealing information about the nature of the land. P waves provide data on overall density and composition, while S waves help identify the material's rigidity. The combination of P and S wave data assists in mapping subsurface layers and understanding geological characteristics.