Which seismic waves cannot move through liquids at all?

Which seismic waves cannot move through liquids at all?

• A. S waves
• B. P waves
• C. Surface waves
• D. Rayleigh waves

Answer: (A)

Seismic waves depend on the medium’s ability to resist shear. S waves are transverse, with particle motion perpendicular to the direction of travel, and they require a material that can sustain shear (a nonzero shear modulus). Liquids can’t resist shear; they flow, so there’s no restoring force for sideways movement. Because of that, S waves cannot propagate through liquids at all—they’re blocked when they encounter a liquid. In contrast, compressional waves move by squeezing and expanding the material and can travel through both solids and liquids, so they do move through liquids. Surface waves and Rayleigh-type motions rely on a solid boundary and its elasticity, so they don’t persist as bulk waves in a liquid either. The key point is that the lack of shear rigidity in liquids prevents transverse (S) waves from propagating.

Seismic waves depend on the medium’s ability to resist shear. S waves are transverse, with particle motion perpendicular to the direction of travel, and they require a material that can sustain shear (a nonzero shear modulus). Liquids can’t resist shear; they flow, so there’s no restoring force for sideways movement. Because of that, S waves cannot propagate through liquids at all—they’re blocked when they encounter a liquid.

In contrast, compressional waves move by squeezing and expanding the material and can travel through both solids and liquids, so they do move through liquids. Surface waves and Rayleigh-type motions rely on a solid boundary and its elasticity, so they don’t persist as bulk waves in a liquid either. The key point is that the lack of shear rigidity in liquids prevents transverse (S) waves from propagating.