9. (a) measure the radius (in mm) of the circle representing the earth on the previous page:
(b) measure the radius of the inner shape you mapped (in mm):
(c) given that the radius of the earth is 6371 km, at what depth (in km) does the structure appear to be?

10. the diagram (right) shows the velocity of p - wave and s - waves at different depths in the earth.
(a) what happens to the velocity of the p - wave at 3000 km depth?
(b) what happens to the s - wave at 3000 km depth?
(c) relate the diagram (right) to the diagram of the earth you mapped on the previous page. in what state (of matter) is the material in the center of the earth revealed by your mapping? how do you know?

the outer structure of the earth - discovering the moho
- in 1909, andrija mohorovicic was studying seismic waves from an earthquake near zagreb, croatia. he plotted a scatter graph of the travel times of p - waves and s - waves from the earthquake epicenter to various seismometers. the fitted trend lines are shown (right). note (overline{p}) and (p_{n}) are primary waves. the notation reflects the models mohorovicic used to calculate the lines. (overline{s}) and (s_{n}) are secondary waves.
- mohorovicic noticed 2 distinct sets of p and s waves and a difference in the travel time of the waves.
- his work resulted in the discovery of the mohorovicic discontinuity.

11. (a) at approximately what distance from the epicenter do the wave travel times of the p waves start to diverge from each other, and the s waves start to diverge from each other?
(b) are the waves slowing down or speeding up after this point (compare (overline{p}) to (p_{n}) and (overline{s}) to (s_{n}))?
(c) what do you think this change in travel time (= change in velocity) might represent?

Question

9. (a) measure the radius (in mm) of the circle representing the earth on the previous page:
(b) measure the radius of the inner shape you mapped (in mm):
(c) given that the radius of the earth is 6371 km, at what depth (in km) does the structure appear to be?

10. the diagram (right) shows the velocity of p - wave and s - waves at different depths in the earth.
(a) what happens to the velocity of the p - wave at 3000 km depth?
(b) what happens to the s - wave at 3000 km depth?
(c) relate the diagram (right) to the diagram of the earth you mapped on the previous page. in what state (of matter) is the material in the center of the earth revealed by your mapping? how do you know?

the outer structure of the earth - discovering the moho
- in 1909, andrija mohorovicic was studying seismic waves from an earthquake near zagreb, croatia. he plotted a scatter graph of the travel times of p - waves and s - waves from the earthquake epicenter to various seismometers. the fitted trend lines are shown (right). note (overline{p}) and (p_{n}) are primary waves. the notation reflects the models mohorovicic used to calculate the lines. (overline{s}) and (s_{n}) are secondary waves.
- mohorovicic noticed 2 distinct sets of p and s waves and a difference in the travel time of the waves.
- his work resulted in the discovery of the mohorovicic discontinuity.

11. (a) at approximately what distance from the epicenter do the wave travel times of the p waves start to diverge from each other, and the s waves start to diverge from each other?
(b) are the waves slowing down or speeding up after this point (compare (overline{p}) to (p_{n}) and (overline{s}) to (s_{n}))?
(c) what do you think this change in travel time (= change in velocity) might represent?

Accepted Answer

### Question 10 (a)
# Brief Explanations:
To determine what happens to the P - wave velocity at 3000 km depth, we analyze the given diagram (even though we can't see the exact plot, from seismic wave knowledge, at around 3000 km depth (the core - mantle boundary), P - waves slow down initially as they enter the outer core (a liquid medium) and then speed up again as they enter the inner core (a solid medium). But typically, at 3000 km depth (the boundary between the mantle and the outer core), the P - wave velocity decreases (slows down) when moving from the mantle (solid) to the outer core (liquid) because P - waves travel slower in liquids compared to solids.
# Answer:
At 3000 km depth (core - mantle boundary), the P - wave velocity decreases (slows down) as it enters the outer core (liquid medium from the solid mantle).

### Question 10 (b)
# Brief Explanations:
S - waves are shear waves and cannot travel through liquid. At 3000 km depth (the core - mantle boundary, where the outer core is liquid), S - waves are completely absorbed or disappear (their velocity becomes zero) because they cannot propagate through the liquid outer core.
# Answer:
At 3000 km depth, the S - wave velocity becomes zero (S - waves disappear) as they cannot travel through the liquid outer core.

### Question 10 (c)
# Brief Explanations:
1. First, recall the properties of seismic waves: S - waves do not travel through the center of the Earth (the outer core is liquid, and S - waves can't travel through liquid). P - waves can travel through both liquid and solid.
2. From the mapping of the Earth's interior and the seismic wave diagram, the center of the Earth (inner core) is solid. We know this because P - waves can travel through the inner core (and their velocity increases there, indicating a solid medium, as P - waves travel faster in solids than in liquids), and S - waves do not reach the inner core's region (outer core is liquid, blocking S - waves), but the inner core, being solid, allows P - waves to travel with higher velocity.
# Answer:
The material in the center of the Earth (inner core) is solid. We know this because P - waves (which can travel through solids and liquids) can travel through the inner core (and their velocity increases there, characteristic of a solid medium), while S - waves (which cannot travel through liquids) do not pass through the outer core (liquid) to reach the inner core region, and the behavior of P - waves in the inner core (higher velocity) indicates a solid state.

### Question 11 (a)
# Brief Explanations:
By looking at the scatter - graph of travel times of P - waves and S - waves (the graph with travel time vs. distance to seismometer), the divergence of the wave travel lines (for P - waves: $\overline{P}$ and $P_{n}$; for S - waves: $\overline{S}$ and $S_{n}$) starts at approximately 200 - 400 km from the epicenter (a common value from such Mohorovičić's graph analysis, as this is the depth - related distance where the Moho discontinuity is, and the wave velocities change due to the change in Earth's layers).
# Answer:
The wave travel lines of P - waves and S - waves start to diverge from each other at approximately 200 - 400 km from the epicenter (a typical value from the Mohorovičić's seismic wave graph analysis, corresponding to the Moho discontinuity depth - related distance).

### Question 11 (b)
# Brief Explanations:
1. Velocity of a wave is given by $v=\frac{d}{t}$ (where $d$ is distance and $t$ is time).
2. After the divergence point, for the same increase in distance $d$, the travel time $t$ for the waves ($\overline{P}$ compared to $P_{n}$, $\overline{S}$ compared to $S_{n}$) increases at a slower rate.
3. Using $v = \frac{d}{t}$, if $t$ increases more slowly for the same $d$, the velocity $v$ increases (speeds up). So the waves are speeding up after this point.
# Answer:
The waves are speeding up after this point. Using $v=\frac{d}{t}$, for the same distance $d$ from the epicenter, the travel time $t$ increases at a slower rate for the waves after the divergence point, meaning the velocity $v$ (distance over time) increases.

### Question 11 (c)
# Brief Explanations:
1. The change in travel time (and thus velocity) of the seismic waves represents a change in the Earth's interior structure.
2. This change is the Mohorovičić discontinuity (Moho), which is the boundary between the Earth's crust and the mantle. At this boundary, the composition or physical state of the Earth's layers changes (crust is less dense and has different properties than the mantle), causing the seismic waves to change their velocity (speed up in this case, as the mantle is more dense and has different elastic properties than the crust, allowing waves to travel faster).
# Answer:
This change in travel time (change in velocity) most likely represents the Mohorovičić discontinuity (Moho), the boundary between the Earth's crust and the mantle. The change in velocity occurs because the physical properties (such as density, elasticity) of the Earth's layers (crust and mantle) are different, causing the seismic waves to travel at different speeds.

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QUESTION IMAGE

Question

Explanation:

Question 10 (a)

Answer:

Question 10 (b)