Then the earth shook and trembled; The foundations of the hills also quaked and were shaken, Because He was angry.
(Psalms 18:7) NKJV
In seismology, S-waves, secondary waves, or shear waves (sometimes called an elastic S-wave) are a type of elastic wave, and are one of the two main types of elastic body waves, so named because they move through the body of an object, unlike surface waves.
– S-wave, definition (Wikipedia)
S-waves, secondary or shear waves, travel through the Earth’s crust and mantle, they can only propagate through solid material. Shear forces don’t exist in liquids or gas.
Here’s a quote from Journeys to the Center of the Earth by Tim Folger for Discover Magazine, about the development of the current theory of the internal structure of the Earth.
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