Which statement best explains why the direction of some seismic waves change sharply as the waves travel through the earth?

Answer 1

As you go deeper within the Earth, the density and rigidity of the constituent material varies. This affects the speed of the seismic waves, and hence causes them to refract (much light how a light beam refracts when it goes from air to a glass block).

Answer 2

This is an attempt at trying to keep the answer as simple and straight-forward as possible - to fully understand the reasoning behind this idea, I recommend reading a good University level textbook on geophysics, such as William Lowrie's Fundamentals of Geophysics. Anyway, here's the jist of it: Seismic waves can be modelled as wavefronts with a general ray that represents the direction in which the wave is travelling (if you are familiar with high-school optics in physics, the concept is essentially the same). When this ray reaches an interface (a boundary between two different types of material), it changes its path: if the medium that it is propagating into allows the wave to travel faster, then the ray refracts (bends) away from the normal (the right-angle intersector to the surface of the interface) - if the wave is going to slow down in the new medium, then it bends towards the normal (This is Snell's law by the way. You can read up on it pretty much anywhere). As the Earth is essentially composed of concentric spheres (lots of spheres that fit inside one another), the waves that propagate through the Earth change direction each time they travel from one layer into another. As a general rule, the deeper one goes into the Earth, the higher the density - and since the velocity of seismic waves is dependant upon the density of the material that it is travelling through (as well the elastic moduli of the material), the velocity increases as density increases. As the wave travels further and further into the Earth, it gets refracted at each interface, always bending away from the normal - until it reaches a limit: as the Earth is a sphere, once you go down deep enough, you start coming out the other end - once you are deep enough, the ray refracts so much that it does not reach the next interface (deeper into the Earth) but instead starts coming out. On the way out, the ray reaches interfaces - each of which slows the ray - and so the ray bends towards the normal. Hence when the number of layers is taken to its limit (to infinity), then the path taken by the ray is essentially a smooth curve.

Answer 3

Because the Earthis made of different composite materials which of the density in each composite material

Answer 4

seismic waves traveled in curved path because on entring in earth their medium change and they refrected

Answer 5

different parts of the earth interior have different densities :)

Answer 6

Whether the objects that are being traveled through are dense or viscous.

Answer 7

seismic waves change speed as they travel through different materials. they travel through liquids only, that is why no seismic waves are recorded in the outer core