What are seismic waves? Does their velocity change as they pass through the Earth? (D)

Seismic waves are waves of energy that travel through the Earth's layers as a result of an earthquake, explosion, or other geological disturbances. They are vibrations that propagate through the Earth and can be detected by seismometers.

There are two main types of seismic waves: body waves and surface waves. Body waves travel through the Earth's interior, while surface waves travel along the Earth's surface. Body waves are further divided into primary (P) waves and secondary (S) waves. P waves are also called compressional waves and can travel through any medium, including solid rock, liquid, and gas. S waves, on the other hand, are called shear waves and can only travel through solid materials.

As seismic waves travel through the Earth, their velocity changes due to variations in the density, elastic properties, and composition of the Earth's layers. P waves generally travel faster than S waves, and both types of body waves travel faster in the deep layers of the Earth, such as the mantle and core, compared to the crust. The velocity of seismic waves is affected by factors such as temperature, pressure, and the minerals composing the Earth's layers. For example, seismic waves slow down when they encounter the mantle's transition zone (around 410 km to 660 km depth) due to changes in the minerals' structures under these conditions. Seismic waves can also be refracted, or bent, when they pass through layers with different velocities. This refraction can help seismologists study the Earth's internal structure by measuring the arrival times of seismic waves at various locations on the Earth's surface. In summary, seismic waves are waves of energy that travel through the Earth's layers as a result of geological disturbances, and their velocity changes as they pass through the Earth, depending on factors such as the density, elastic properties, and composition of the Earth's layers.