The motion of particles in a shear wave is

• A. Transverse to the direction of beam propagation
• B. Parallel to the direction of propagation
• C. Elliptical motion in surface
• D. Polarized 45 degrees to the direction of beam propagation

Answer: (A)

In a shear wave, particle displacement is perpendicular to the direction the wave travels. This transverse motion means particles oscillate side-to-side or up-and-down in a plane that is orthogonal to the propagation direction. This is different from longitudinal waves, where motion is parallel to the travel direction, and from Rayleigh surface waves, where the motion is elliptical within the surface plane. A polarization angle like 45 degrees to the propagation would include a component along the travel direction, which isn’t characteristic of a pure shear wave.