Which statement about S-waves is true?

• A. They travel through liquids
• B. They travel only through solids
• C. They travel at the speed of light
• D. They cause no damage

Answer: (B)

S-waves are shear waves, so the material they move twists side-to-side as the wave passes. This sideways motion requires a medium that can resist shear forces, i.e., a solid with rigidity. Liquids can’t sustain shear in the same way, so S-waves cannot propagate through them. That’s why they don’t travel through the Earth’s liquid outer core, leading to the S-wave shadow zone observed after earthquakes. They move slower than P-waves and are not as fast as light. They do contribute to ground shaking and can cause damage, so the idea that they cause no damage isn’t accurate. Because they only propagate through solids, the statement is true.