At the top and bottom horizontal axes, the seismic velocity, or the speed of tra
ID: 296442 • Letter: A
Question
At the top and bottom horizontal axes, the seismic velocity, or the speed of travel of the earthquake waves within the Earth, is shown as kilometers per second (km s-1). The depth, at which waves appear, is shown as kilometers. The top of the graph represents the surface of the Earth (Earth’s crust), the bottom represents the center of the Earth.
Depths of the Earth’s interior with P and S wave characteristics(left); Earth’s known interior with depths(right)
For the following questions, choose the correct answer in the parentheses by highlighting.
Layer A is called the (core, mantle, lithosphere).
Layer B is called the (crust, asthenosphere, outer core).
The velocity of P and S waves (increases, decreases) immediately in layer B just below layer A.
How can you tell layer C is liquid?
What happens to S waves when they reach layer D, and what does this tell us about layer D?
On the graph above left, how do the depths where seismic velocity abruptly change correlate to the known layers of the Earth’s interior?
Seismic velocities km s-1 0 246 8 1012 14 Inner core Outer core Mantle Crust 2000 Depth 3000 800 miles (1,300 kilometers) 1,400 miles (2.250 kilometers) 1,800 miles (2.900 kilometers) 5 to 25 miles (8to 40 kilometers)Explanation / Answer
1) Layer A is called the lithosphere.
2) Layer B is called the asthenosphere.
3) The velocity of P and S waves decreases immediately in layer B just below layer A. Because low velocity zone is present within the asthenosphere in the upper mantle, varies in between 50 and 250 km depth. It consists of 5% liquid. For that reasons, S- and P-wave velocities are reduced.
4) Mode of propagation of P wave is compression and rarefaction of particles within the Earth. So, they can travel through solids and liquids but travel more slowly through liquids than solids. But S wave are propagated by shear, or motion which is at right angles to the wave travel direction. So, S wave can not be moved through liquid medium. From this idea we can tell C layer is liquid. In graph, S wave line disappear
5) When S wave enters to layer D, its Velocity increases at the boundary of outer core (layer C) and inner core (layer D). Then it Passes uniformly as the inner core is solid made up of iron and nickel.
6) On the graph above left, the depths where seismic velocity abruptly change correlate to the known layers of the Earth’s interior is given below;
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