Can S waves travel through the asthenosphere?

As a geophysicist with expertise in seismology, I can explain the behavior of seismic waves within the Earth's layers. The asthenosphere is a part of the Earth's mantle that is characterized by its ability to flow, albeit very slowly. Despite this flow, the asthenosphere is not a liquid but rather a solid that behaves plastically over long periods of time. This means that it can transmit both types of seismic body waves: S-waves (shear or secondary waves) and P-waves (primary or pressure waves). The ability of the asthenosphere to transmit S-waves is significant because S-waves cannot travel through liquids, but they can travel through solids. The statement that "both S- and P-waves can travel through it" is correct. However, it is important to note that the asthenosphere's capacity to transmit S-waves does not mean it is a liquid; it is a solid that can deform under stress over geological timescales. At a depth of around 660 kilometers, the Earth's mantle transitions into a more rigid layer known as the mesosphere. Here, the pressure is so high that the mantle behaves more like a solid and can no longer flow to the same extent as the asthenosphere above it. This transition affects the propagation of seismic waves, as the mesosphere will not allow S-waves to pass through it, while P-waves can still travel. In summary, **S-waves can indeed travel through the asthenosphere**, but not through the mesosphere at depths below approximately 660 kilometers.

It is important to note that although the asthenosphere can flow, it is not a liquid, and thus both S- and P-waves can travel through it. At a depth of around 660 km, the pressure becomes so great that the mantle can no longer flow, and this solid part of the mantle is called the mesosphere.