Earthquake waves travel at different velocities through different parts of Earth. This difference is based mostly on

density differences among rock materials

the types of nearby plate boundaries

environmental conditions such as temperature and air pressure

whether or not the waves travel through water

Option (1)

Explanation:

During an earthquake, the seismic waves travel through the different layers inside the earth at different velocities. This change in velocity is due to the variation in the differences in the densities of the rocks.

The earth's interior is divided into-

1) Crust - It is the top portion of the earth and the rocks have a density of about 2.5 g/cm³.

2) Mantle - The mantle is also separated into the upper mantle (density is about 3.9g/cm³) and lower mantle (density of almost 5.1 g/cm³).

3) Core - The core of the earth is very hot and comprised of molten materials and is divided into the inner core which has a density of about 13g/cm³ and outer core that has a density of approximately 11g/cm³.

The P waves can travel both in solid (crust, mantle, inner core) as well as liquid (outer core) and are faster than the S waves. But, S waves can travel only in solid and these waves are absorbed when they reach the core-mantle boundary.

Thus, the correct answer is option (1).

The difference is based mostly on density differences among rock materials.