Seismic velocity involves the deformation of a rock as a function of time. Compressional stress, which changes both volume and shape, leads to P-wave velocity, and shear stress, which changes shape but not volume, leads to S-wave velocity.

• Seismic velocity involves the deformation of a rock as a function of time. Compressional stress, which changes both volume and shape, leads to P-wave velocity, and shear stress, which changes shape but not volume, leads to S-wave velocity.