Deck 23: The Earth’s Interior Revisited: Insights from Geophysics

Question 1

The time it takes for a seismic wave to travel from the focus of an earthquake to a seismometer is called the ________.

A) wave front time
B) P-S wave arrival distance
C) travel time
D) seismic ray time

Answer 1

C

Question 2

The subdiscipline of geology that investigates the Earth's physical characteristics such seismic waves,gravity,and magnetism is termed _______.

A) tectonics
B) seismography
C) mineralogy
D) geophysics

Answer 2

D

Question 3

If a P-wave is traveling through the Earth and encounters a molten magma chamber,what will happen to the velocity of the P-wave?

A) It will decrease.
B) It will increase.
C) It will stay at a constant speed.
D) It will drop to zero.

Answer 3

A

Question 4

What behavior will seismic waves exhibit when traveling from a lower-velocity material into a high-velocity material?

A) The seismic waves will not travel into the higher-velocity material.
B) The direction the waves are traveling will bend away from the boundary.
C) The direction the waves are traveling will bend toward the boundary
D) The seismic waves will be reflected back in the direction they were coming from.

Question 5

In the picture below,when the ship is filled with cargo it sinks into the water until the mass of water displaced is equal to the mass of the cargo.The ship is then said to be ________.

A) an equipotential surface
B) in freeboard balance
C) equal to the geoid
D) in isostatic equilibrium

Question 6

You are studying the seismic data from Mars when you notice that there are no S-waves recorded from 130° through 180° on the opposite side of the planet.What does this information tell you about the interior of Mars?

A) There is a layer of solid material in the interior of Mars.
B) There is a layer of liquid material in the interior of Mars.
C) There is a layer with a higher-velocity material than the crust below.
D) There is a layer with a lower-velocity material than the crust below.

Question 7

Using the graph below,why is the outer core liquid,but the inner core solid?

A) because the inner core is made of different material than the outer core
B) because the temperature in the inner core is above that of the melting curve
C) because the temperature in the inner core is below that of the melting curve
D) because the pressure on the inner core is lower

Question 8

The graph below shows the change in velocity of seismic waves with depth in the crust.Why does the velocity of the P-wave drop drastically at the core-mantle boundary?

A) because the core is much denser than the mantle
B) because the outer core is solid and P-waves can't pass through solids
C) because the outer core is liquid and seismic waves travel slower in liquids
D) because the S-waves are removed and that energy is transferred to the P-waves

Question 9

What causes the velocity of a P-wave to increase when it enters the inner core?

A) The inner core is a much more dense material than the outer core.
B) The inner core is a much less dense material than the outer core.
C) The inner core is liquid,and thus the wave speeds up.
D) The P-wave no longer has to compete with the S-wave for energy.

Question 10

Seismic waves travel ________ in solids than in liquids; however,unlike P-waves,S-waves ________ travel through liquids.

A) slower; can
B) slower; can't
C) faster; can
D) faster; can't

Question 11

In the following graph,why does the line for S-waves NOT appear in the outer core?

A) S-waves can't travel through the outer core because it is solid.
B) S-waves can't travel through the outer core because it is liquid.
C) S-waves disappear after being reflected at the core-mantle boundary.
D) S-waves can't travel that far into the Earth due to the high amount of iron.

Question 12

A mountain range made of high-density basalt would produce a(n)________ gravity anomaly compared to a mountain range of lower-density sedimentary rocks.

A) positive
B) negative
C) isostatic
D) magnetized

Question 13

If an S-wave is traveling through rock when it encounters a molten magma chamber,what will happen to the velocity of the S-wave?

A) It will slow down.
B) It will speed up.
C) It will remain at the same speed.
D) It will not travel through the magma.

Question 14

Which of the following best describes how scientists study the interior of the Earth?

A) Scientists dig deep holes to access and study the Earth's interior.
B) Scientists use seismic waves,gravity,and magnetism to study the Earth's interior.
C) Scientists use only seismic waves and gravity to study the Earth's interior.
D) Scientists use seismic waves alone to study the Earth's interior.

Question 15

The Earth's gravity is best represented by an equipotential surface that contains bumps and depressions where areas of higher or lower gravity appear over the Earth.This representation is called the ________.

A) reference geoid
B) gravitational potential
C) isostasy
D) geoid

Question 16

If a ship weighs 52,000 tons and is in isostatic equilibrium when 6,000 tons of cargo is added,what is the total mass of water that will be displaced by the ship after the cargo is added?

A) 6,000 tons
B) 12,000 tons
C) 58,000 tons
D) 52,000 tons

Question 17

The core consists of two layers: a(n)________ inner core and a(n)________ outer core.

A) iron; nickel
B) nickel; iron
C) solid; liquid
D) liquid; solid

Question 18

Which layer of the Earth has the highest density?

A) atmosphere
B) crust
C) mantle
D) core

Question 19

If a S-wave is traveling through sandstone and then encounters peridotite,the S-wave will ________.

A) slow down
B) speed up
C) remain at the same speed
D) not travel through the peridotite

Question 20

If a gravity anomaly is negative,what does that imply about the material underground?

A) The material is much more dense rock.
B) The material is much less dense rock.
C) The material is an underground ore.
D) The material is composed of mantle.

Question 21

If a P-wave is traveling up toward Earth's surface from a layer of mantle peridotite to a layer of limestone crust,what will happen to the P-wave in terms of speed and direction of motion? Why?

Question 22

Why are magnetic anomalies of continental crust so much more complicated than those of oceanic crust?

A) The continents are much older and thus have had more time for the minerals to become magnetized.
B) The continents contain abundant iron minerals,whereas the oceanic crust does not contain any iron minerals.
C) The continents contain a random orientation of minerals that become magnetized when they interact with the magnetic field.
D) The continents contain a complex distribution of igneous intrusions,lava flows,and iron-rich sediments.

Question 23

During the last ice age,continental glaciers covered significant portions of the North American continent.In the context of Archimedes' principle,what effect would these glaciers have had on the lithosphere relative to the asthenosphere? How was isostatic equilibrium achieved?

Question 24

Imagine that you are an economic geologist,trying to find copper resources.How might gravity anomalies help you?

Question 25

Using the image below,explain why the P-wave velocity drops drastically at the outer core-mantle boundary.Also,explain why the P-wave velocity speeds up at the inner core-outer core boundary.

Question 26

The Earth's magnetic field is produced in the ________.

A) crust
B) mantle
C) outer core
D) inner core

Question 27

Why would the gravity anomaly over a deep-ocean trench be negative?

A) because the bathymetry of the trench dips very far below sea level
B) because the crust being pulled into the trench is less dense than sediments above
C) because water fills the space above the subducting slab and is much less dense than rock
D) because the buoyant magma created at the subduction zones is less dense than the rock

Question 28

Kilauea Volcano in Hawaii has been erupting large volumes of basaltic lava over the past few decades.Would the magnetic anomaly associated with this recent volcanism be positive or negative? Why?

Question 29

A positive magnetic anomaly is produced when the measured magnetic field strength is ________ the expected magnetic field strength.

A) stronger than
B) weaker than
C) the same as
D) the opposite of

Question 30

If you measure the magnetization of an area of igneous rocks and find a large negative anomaly,what does that imply about the rocks?

A) They were formed during a time of normal polarity of the magnetic field.
B) They were formed during a time of reversed polarity of the magnetic field.
C) They were formed on the ocean floor where the rocks are closer to the core.
D) They were formed on the continental crust in a complex pattern of magnetization.