The graph below shows the change in velocity of seismic waves with depth in the crust.Why does the velocity of the P-wave drop drastically at the core-mantle boundary?
A) because the core is much denser than the mantle
B) because the outer core is solid and P-waves can't pass through solids
C) because the outer core is liquid and seismic waves travel slower in liquids
D) because the S-waves are removed and that energy is transferred to the P-waves

Question

The graph below shows the change in velocity of seismic waves with depth in the crust.Why does the velocity of the P-wave drop drastically at the core-mantle boundary? 
A) because the core is much denser than the mantle 
B) because the outer core is solid and P-waves can't pass through solids 
C) because the outer core is liquid and seismic waves travel slower in liquids 
D) because the S-waves are removed and that energy is transferred to the P-waves

Quizplus · Accepted Answer

The drop in velocity of P-waves at the core-mantle boundary is due to the fact that the outer core is liquid, and seismic waves travel slower in liquids than in solids. This is not the case for S-waves, which cannot propagate through liquids, and therefore experience a complete drop in velocity at the core-mantle boundary. The density contrast between the core and mantle (option A) does affect wave propagation velocities but is not the main reason why P-wave velocity drops at the core-mantle boundary. Option B (solid outer core) is incorrect as P-waves can propagate through solids. Option D (energy transfer from S-waves to P-waves) is also incorrect as the two types of waves propagate differently and can't exchange energy directly.

The Graph Below Shows the Change in Velocity of Seismic