P-wave Velocity Comparison in Earth's Layers

Seismic P-waves (primary waves) travel through Earth's interior. Their speed depends on the density and elastic properties of the material they pass through.

• Lower Mantle (V_m): P-wave velocities increase with depth due to rising pressure and density. Velocities typically range from approximately 8 km/s to 11 km/s.
• Outer Core (V_o): The outer core is liquid. P-waves slow down significantly upon entering this layer because liquids have lower shear strength than solids. Velocities drop to around 8 km/s to 10 km/s.
• Inner Core (V_i): The inner core is solid, despite its high temperature. Increased rigidity and density cause P-wave velocities to increase again, reaching about 10 km/s to 13 km/s.

Determining Velocity Order

Comparing the typical velocity ranges:

• The velocity in the lower mantle (V_m) is generally higher than in the outer core (V_o).
• The velocity in the inner core (V_i) is higher than in the outer core (V_o).
• While $V_m$ and $V_i$ can overlap, generally $V_m$ represents velocities in the denser, solid lower mantle, and $V_i$ represents velocities in the solid inner core. Based on common seismic models, the lower mantle velocity is typically greater than the inner core velocity, which is greater than the outer core velocity.

Therefore, the correct relationship is:

V_m > V_i > V_o