Question

an earthquake generates a seismic wave that travels through several layers of the earth’s interior, shown below.
earth’s layers
the lithosphere is made out of solid rock, the mantle is a combination of solids and liquids, and the outer core is a liquid.
the path of the seismic wave changes at the boundaries of each layer because
a. the layers are different sizes.
b. each layer has different properties.
c. each layer is made out of the same material.
d. seismic waves always change direction after a few miles.

Explanation:

To determine why the seismic wave's path changes at layer boundaries, we analyze each option:

• Option A: Layer size doesn't directly cause wave path change. Seismic wave behavior is about material properties, not size. Eliminate A.
• Option B: Earth's layers (lithosphere, mantle, outer core, inner core) have different properties (e.g., solid, liquid, varying density). Seismic waves refract (change direction) at boundaries between materials with different properties (like from solid to liquid or different densities). This matches the reason for path change.
• Option C: Layers are made of different materials (e.g., lithosphere: solid rock; mantle: solid - liquid mix; outer core: liquid; inner core: solid). So C is incorrect.
• Option D: The change in direction is due to crossing layer boundaries (different material properties), not a fixed "few miles" distance. The distance depends on the layer boundary, not a set mileage. Eliminate D.

Answer:

B. each layer has different properties.