Chapter 8: Earthquakes Slide Set 7

Question 1

Identify the FALSE statement.

A. Tectonic plates interact at their boundaries.
B. Plate boundaries often coincide with earthquake
locations.
C. Lithospheric plates are constantly moving.
D. The shape of lithospheric plates remains the same over
time.

Answer 1

D

Question 2

Where is sediment on the sea floor the thinnest?

A. by the oceanic trenches
B. close to oceanic ridges
C. on the abyssal plain
D. None of the options is correct. Sea-floor sediment
thickness is even throughout the ocean basin.

Answer 2

B

Question 3

Oceanic lithosphere…
A. is thicker than continental lithosphere.
B. Is more buoyant than continental lithosphere.
C. is more dense than continental lithosphere.
D. has a granitic composition.
E. is older than most continental lithosphere.

Answer 3

C

Question 4

Hot spots…
A. are plumes of upwelling mantle that move over time.
B. are linked to plate boundaries.
C. create lines of volcanic islands, such as Hawaii.
D. cannot be explained by plate-tectonic theory.
E. are made of felsic magma from the upper mantle.

Answer 4

a

Question 5

What is an earthquake?

Answer 5

Vibration of the Earth produced by the rapid release of energy)

Question 6

What causes the earthquake to occur?

Answer 6

The energy released by atomic explosions, large landslides or by volcanic eruptions can produce an earthquake, but the sudden movement along faults is the cause of most earthquakes

Question 7

Explain the earthquakes in terms of stress, strain and fracture

Answer 7

The formation and movement of faults causes most destructive earthquakes. When the strength of the rock is exceeded, there is failure and release of the strain by sudden dislocation or fracture along the fault plane.

Question 8

Earth shaking is caused by __________, most of which is due to _______.

Answer 8

a rapid release of energy

tectonic forces

Question 9

Most earthquakes result from _______.

Answer 9

tectonic plate motion

Question 10

Seismicity (earthquake activity) occurs due to:

Answer 10

• Sudden motion along a newly formed crustal fault.
• Sudden slip along an existing fault.
• A sudden change in mineral structure.
• Movement of magma in a volcano.
• Volcanic eruption.
• Giant landslides.
• Meteorite impacts.
• Nuclear detonations.

Question 11

What is the most common cause of earthquake activity?

Answer 11

Fault slip is the most common cause.

Question 12

What is hypocenter (focus)?

Answer 12

The hypocenter (or focus) is the location where fault slip occurs. It is usually on a fault surface.

Question 13

What is epicenter?

Answer 13

The epicenter is the land surface directly above the hypocenter. Maps often portray the location of epicenters.

Question 14

What are faults?

Answer 14

Faults are crustal breaks where movement occurs.

Question 15

______ is the ground surface expression of a fault.

Answer 15

Fault trace

Question 16

On a sloping fault, crustal blocks are classified as:

Answer 16

• Footwall (block below the fault).

- Hanging wall (block above the fault).

Question 17

On a ______ fault, the hanging wall moves down relative to the footwall. It most often results from extension (pull-apart or stretching).

Answer 17

normal

Question 18

In a ______ fault, the hanging wall moves up relative to the footwall. It usually results from compression (squeezing or shortening).

Answer 18

reverse

Question 19

Hanging wall (block above/below the fault)

Answer 19

above

Question 20

Footwall (block above/below the fault)

Answer 20

below

Question 21

A ______ fault is a special kind of reverse fault that has a lower angle slope (dip). It’s a common fault type in compressional mountain belts.

Answer 21

thrust

Question 22

Along a ________ fault, one block slides laterally past the other block. There is no vertical motion across the fault.

Answer 22

strike-slip

Question 23

Strike-slip faults tend to be close to vertical/horizontal. The motion across the fault, however, is not vertical/horizontal but vertical/horizontal.

Answer 23

vertical
vertical
horizontal

Question 24

The _______ (or offset) is the amount of movement across a fault

Answer 24

displacement

Question 25

What is the difference between active and inactive faults?

Answer 25

• Active faults—ongoing stresses produce motion.

- Inactive faults—motion occurred in the geologic past.

Question 26

Displacement at the land surface creates a _____.

Answer 26

fault scarp

Question 27

True/False

All faults reach the surface

Answer 27

False

Not all faults reach the surface. Blind faults are invisible.

Question 28

_______ shows the fault intersecting the ground.

Answer 28

Fault trace

Question 29

How is the earthquake energy generated? Explain the steps

Answer 29

• The rock bends slightly without breaking (elastic).
• Continued stress causes cracks to develop and grow.
• Eventually, cracking progresses to the point of failure.
• Stored elastic energy is released at once, creating a fault.