GEOLOGY

Detailed explanation-1: -Seismic waves travel a curving path through the earth due to changes in composition, pressure, and temperature within the layers of the Earth. Seismic waves travel at different speeds through different materials. In this 2-layer model two wave fronts leave an impact at the same time but the lower layer is faster.

Detailed explanation-2: -2. Figure 19.2: The earth, however, is compositionally layered and the density of rocks, particularly in the mantle, generally increases with depth. As a result, seismic waves bend and reflect as they travel through the earth.

Detailed explanation-3: -Because velocity generally increases with depth in the mantle, the wave paths get bent until they reach a critical angle at which point, the waves return to the surface following a curved path upward. Various material properties (i.e., elastic moduli) control the speed and attenuation of seismic waves.

Detailed explanation-4: -The waves are refracted as they travel through the Earth due to a change in density of the medium. This causes the waves to travel in curved paths. When the waves cross the boundary between two different layers, there is a sudden change in direction due to refraction.

Detailed explanation-5: -The direct P wave arrives first because its path is through the higher speed, dense rocks deeper in the earth. The PP (one bounce) and PPP (two bounces) waves travel more slowly than the direct P because they pass through shallower, lower velocity rocks.