What distinguishes P-waves from S-waves?

P-waves and S-waves are both types of seismic waves generated by earthquakes, but they exhibit distinct behaviors and characteristics.

P-waves, or primary waves, are characterized as compressional waves. This means they move through materials by compressing and expanding the medium in the direction the wave is traveling. This unique motion allows P-waves to travel through both solids and liquids, making them the fastest seismic waves and the first to be detected by seismographs during an earthquake. This ability to travel through different states of matter is critical in understanding the Earth's internal structure, as it indicates that the outer core is liquid, evidenced by the behavior of P-waves.

In contrast, S-waves, or secondary waves, are shear waves that move the ground up and down or side to side, which requires a solid medium to propagate. Because of this, S-waves can only travel through solids and are unable to pass through liquids. This distinction is crucial in seismology for determining the different layers of the Earth.

Thus, option B accurately describes the fundamental differences between P-waves and S-waves regarding their modes of travel and the states of matter through which they can propagate.