How do seismic wave speeds change with depth, and what does this imply about Earth's interior?

How do seismic wave speeds change with depth, and what does this imply about Earth's interior?

• A. Wave speeds generally increase with depth due to increasing rigidity and density.
• B. Wave speeds decrease with depth due to cooling.
• C. P-waves slow while S-waves speed up with depth.
• D. Seismic wave speeds remain constant with depth.

Answer: (A)

Seismic wave speeds rise with depth because increasing pressure makes rocks denser and much stiffer (elastic moduli increase). That combination speeds up both P-waves and S-waves as you go deeper, especially through the solid mantle. This pattern supports a layered Earth: a solid, velocity-increasing mantle, a liquid outer core that stops S-waves (so they don’t travel through it), and a solid inner core where speeds are very high. The idea that speeds would decrease with depth, stay constant, or that P- and S-waves would shift in opposite ways doesn’t fit the way rock properties change under pressure in Earth’s interior.

Seismic wave speeds rise with depth because increasing pressure makes rocks denser and much stiffer (elastic moduli increase). That combination speeds up both P-waves and S-waves as you go deeper, especially through the solid mantle. This pattern supports a layered Earth: a solid, velocity-increasing mantle, a liquid outer core that stops S-waves (so they don’t travel through it), and a solid inner core where speeds are very high. The idea that speeds would decrease with depth, stay constant, or that P- and S-waves would shift in opposite ways doesn’t fit the way rock properties change under pressure in Earth’s interior.