Question

1. Explain why no S-waves are received on the side of the Earth opposite the epicentre.

2. Explain why no P-Waves are received on the area labelled “Shadow Zone.”

3. Explain what causes seismic waves to travel along curved paths instead of straight lines.

4. What is the relationship between rock density and the velocity of the seismic waves?

5. Is the shadow zone always in the same location on Earth? Explain.

Answer 1

Answer:

1. The primary seismic waves are refracted by the liquid outer core of the Earth and are not detected between 104° and 140° (between approximately 11,570 and 15,570 km or 7,190 and 9,670 mi) from the epicenter. ... and so S-wave velocity is entirely dependent on the rigidity of the material it travels through.
2. A seismic shadow zone is an area of the Earth's surface where seismographs can only barely detect an earthquake after its seismic waves have passed through the Earth. ... P-waves that have been converted to S-waves on leaving the outer core may be detected beyond 140 degrees.
3. 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.
4. Plots of seismic velocity and density of rock samples show that a range of densities is possible for rocks of each seismic velocity and vice versa, although a single linear relationship is often assumed in crustal gravity calculations.
5. A seismic shadow zone is not in a constant place; each earthquake epicenter has a different shadow zone. The finding of shadow zones allowed scientists to prove Earth had an interior layer of liquid.

Explanation: