stress in earths crust

oceanic plate subduction

Volcanic mountain ranges form when oceanic crust is pushed down into the mantle at convergent plate boundaries. The Andes Mountains are a chain of coastal volcanic mountains. They are forming as the Nazca plate subducts beneath the South American plate (Figure 7.18).

continentcontinent convergence

Most of the worlds largest mountains form as plates collide at convergent plate boundaries. Continents are too buoyant to get pushed down into the mantle. So when the plates smash together, the crust crumples upwards. This creates mountains. Folding and faulting in these collision zones makes the crust thicker. The worlds highest mountain range, the Himalayas, is growing as India collides with Eurasia. About 80 million years ago, India was separated from Eurasia by an ocean (Figure 7.16). As the plates collided, pieces of the old seafloor were forced over the Asian continent. This old seafloor is now found high in the Himalayas (Figure 7.17).

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rifting

Mid-ocean ridges form at divergent plate boundaries. As the ocean floor separates an enormous line of volcanoes is created. When continental crust is pulled apart, it breaks into blocks. These blocks of crust are separated by normal faults. The blocks slide up or down. The result is alternating mountain ranges and valleys. This topography is known as basin-and-range (Figure 7.19). The area near Death Valley, California is the center of a classic basin-and-range province (Figure 7.20).

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causes and types of stress

Stress is the force applied to a rock. There are four types of stresses: Confining stress happens as weight of all the overlying rock pushes down on a deeply buried rock. The rock is being pushed in from all sides, which compresses it. The rock will not deform because there is no place for it to move. Compression stress squeezes rocks together. Compression causes rocks to fold or fracture (Figure 7.1). When two cars collide, compression causes them to crumple. Compression is the most common stress at convergent plate boundaries. Tension stress pulls rocks apart. Tension causes rocks to lengthen or break apart. Tension is the major type of stress found at divergent plate boundaries. Shear stress happens when forces slide past each other in opposite directions (Figure 7.2). This is the most common stress found at transform plate boundaries. The amount of stress on a rock may be greater than the rocks strength. In that case, the rock will change and deform (Figure 7.3). Deep within the Earth, the pressure is very great. A rock behaves like a stretched rubber band. When the stress stops, the rock goes back to its original shape. If more stress is applied to the rock, it bends and flows. It does not return to its original shape. Near the surface, if the stress continues, the rock will fracture and break.

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folds

Deep within the Earth, as plates collide, rocks crumple into folds. You can model these folds by placing your hands on opposite edges of a piece of cloth and pushing your hands together. In sedimentary rocks, you can easily trace the folding of the layers. In the Figure 7.6, the rock layers are no longer horizontal. They tilt downhill from right to left in a monocline. Once rocks are folded, they do not return to their original shape. There are three types of folds: monoclines, anticlines, and synclines. A monocline is a simple one step bend in the rock layers (Figure 7.7). In a monocline, the oldest rocks are still at the bottom and the youngest are at the top. An anticline is a fold that arches upward. The rocks dip away from the center of the fold (Figure 7.8). The oldest rocks are found at the center of an anticline. The youngest rocks are draped over them at the top of the structure. When upward folding rocks form a circular structure, that structure is called a dome. If the top of the dome is eroded off, the oldest rocks are exposed at the center. A syncline is a fold that bends downward (Figure 7.9). In a syncline, the youngest rocks are at the center. The oldest rocks are at the outside edges. When rocks bend downward in a circular structure, it is called a basin. If the rocks are eroded, the youngest rocks are at the center. Basins can be enormous, like the Michigan Basin.

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geologic structures

Sedimentary rocks are formed in horizontal layers. This is magnificently displayed around the southwestern United States. The arid climate allows rock layers to be well exposed (Figure 7.4). The lowest layers are the oldest and the higher layers are younger. Folds, joints and faults are caused by stresses. Figure 7.5 shows joints in a granite hillside. If a sedimentary rock is tilted or folded, we know that stresses have changed the rock (Figure 7.6).

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strikeslip

A strike-slip fault is a dip-slip fault where the dip of the fault plane is vertical. Strike-slip faults result from shear stresses. If you stand with one foot on each side of a strike-slip fault, one side will be moving toward you while the other side moves away from you. If your right foot moves toward you, the fault is known as a right-lateral strike-slip fault. If your left foot moves toward you, the fault is a left-lateral strike-slip fault (Figure 7.14).

faults

With enough stress, a rock will fracture, or break. The fracture is called a joint if the rock breaks but doesnt move, as shown in Figure 7.10. If the rocks on one or both sides of a fracture move, the fracture is called a fault (Figure 7.11). Faults can occur alone or in clusters, creating a fault zone. Earthquakes happen when rocks break and move suddenly. The energy released causes an earthquake. Slip is the distance rocks move along a fault, as one block of rock moves past the other. The angle of a fault is called When compression squeezes the crust into a smaller space, the hanging wall pushes up relative to the footwall. This creates a reverse fault. A thrust fault is a type of reverse fault where the angle is nearly horizontal. Rocks can slip many miles along thrust faults (Figure 7.13).

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stress and mountain building

Many processes create mountains. Most mountains form along plate boundaries. A few mountains may form in the middle of a plate. For example, huge volcanoes are mountains formed at hotspots within the Pacific Plate.

san andreas fault

The San Andreas Fault in California is a right-lateral strike-slip fault (Figure 7.15). It is also a transform fault because the San Andreas is a plate boundary. As you can see, California will not fall into the ocean someday. The land west of the San Andreas Fault is moving northeastward, while the North American plate moves southwest. Someday, millions of years from now, Los Angeles will be a suburb of San Francisco!

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instructional diagrams

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Rocks are present all over earth and sometimes stress causes damage to them. Stress can occur to rocks when force is applied to them. There are four types of rock stresses. They are: confining stress, compression stress, tension stress and shear stress. Confining stress occurs when other rocks push down on a rock below them. Compression stress occurs when rocks are pressed together. Tension stress occurs when rocks are forced apart. Shear stress occurs when two or more rocks are forced in opposite directions.

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The diagram shows different types of geological faults. Reverse fault is the geologic fault in which the hanging wall has moved upward relative to the footwall. Hanging wall is the block of rock that lies above an inclined fault while footwall is the block of rock that lies on the underside of an inclined fault. Reverse faults occur where two blocks of rock are forced together by compression. Normal fault is the geologic fault in which the hanging wall has moved downward relative to the footwall. Normal faults occur where two blocks of rock are pulled apart, as by tension. Strike-slip fault is the geologic fault in which the blocks of rock on either side of the fault slide horizontally in opposite directions along the line of the fault plane.

description_image

The image below shows different types of faults. A fault is a planar fracture or discontinuity in a volume of rock, across which there has been significant displacement as a result of rock mass movement. Large faults within the Earth's crust result from the action of plate tectonic forces, with the largest forming the boundaries between the plates, such as subduction zones or transform faults. Energy release associated with rapid movement on active faults is the cause of most earthquakes. In strike-slip faults the fault surface is usually near vertical and the footwall moves either left or right or laterally with very little vertical motion. Strike-slip faults with left-lateral motion are also known as sinistral faults. In a normal fault, the block above the fault moves down relative to the block below the fault. This fault motion is caused by tensional forces and results in extension.

questions

The most common stress at divergent plate boundaries is

-->  a. tension stress.

b. compression stress.

c. shear stress.

d. confining stress.

As a rock experiences more stress it

a. deforms plastically, then elastically, then breaks

b. breaks, then deforms plastically, then elastically

-->  c. deforms elastically, then plastically, then breaks

d. breaks, then deforms elastically, then plastically

Stresses change rock by causing

a. folds.

b. faults.

c. fractures.

-->  d. all of the above

In the Grand Canyon, the Kaibab Limestone is above the Toroweap Formation. We can say that

a. the Kaibab is the oldest rock layer in the canyon

b. the Toroweap is the oldest rock layer in the canyon

c. the Kaibab is older than the Toroweap

-->  d. the Toroweap is older than the Kaibab

A fold that bends downward is known as a(n)

a. monocline.

-->  b. syncline.

c. anticline.

d. incline.

When rocks deform plastically, they tend to

a. return to their original state.

-->  b. fold

c. break

d. fracture

In a normal fault,

a. the fault plane is roughly vertical

b. the dip of the fault plane is nearly horizontal

c. the hanging wall pushes up relative to the footwall

-->  d. the footwall pushes up relative to the hanging wall

A place where rock breaks but doesnt move it is called a

a. fold.

b. fault.

-->  c. joint.

d. confinement.

A fracture becomes a fault only if rock

a. cracks.

-->  b. moves.

c. folds.

d. deforms.

Large mountain ranges, like the Grand Tetons in Wyoming, are uplifted on

-->  a. normal faults

b. reverse faults

c. dip-slip faults

d. strike-slip faults

Which statement about the San Andreas fault is false?

a. It is a transform fault.

b. It is a strike-slip fault.

c. It occurs at a plate boundary.

-->  d. none of the above

Most of the worlds largest mountains formed at

-->  a. convergent plate boundaries.

b. divergent plate boundaries.

c. transform plate boundaries.

d. confining plate boundaries

If very old rocks are above much younger rocks there may be a thrust fault in between.

-->  a. true

b. false

A deeply buried rock is under compressive stresses.

-->  a. true

b. false

The terrain known as basin-and-range is caused by compressive forces.

a. true

-->  b. false

The amount the ground moves in an earthquake is called slip.

-->  a. true

b. false

In a strike-slip fault, the dip of the fault plane is vertical.

-->  a. true

b. false

Any force applied to rock is a stress.

-->  a. true

b. false

When confining stress occurs, rock deforms.

a. true

-->  b. false

Compression is the most common stress at convergent plates.

-->  a. true

b. false

Stress is the cause of joints in rock.

-->  a. true

b. false

A syncline is a fold that arches upward.

a. true

-->  b. false

An area where faults are clustered is called a fault zone.

-->  a. true

b. false

Movement of rock at faults is the cause of earthquakes.

-->  a. true

b. false

Normal faults are caused by compression stress.

a. true

-->  b. false

Strike-slip faults result from shear stress.

-->  a. true

b. false

Only the process of folding creates mountain ranges.

a. true

-->  b. false

fault in which the hanging wall drops down relative to the footwall

a. dip-slip fault

-->  b. normal fault

c. reverse fault

d. strike-slip fault

e. thrust fault

f. hanging wall

g. footwall

block of rock that is beneath a dip-slip fault plane

a. dip-slip fault

b. normal fault

c. reverse fault

d. strike-slip fault

e. thrust fault

f. hanging wall

-->  g. footwall

fault in which the hanging wall pushes up relative to the footwall

a. dip-slip fault

b. normal fault

-->  c. reverse fault

d. strike-slip fault

e. thrust fault

f. hanging wall

g. footwall

block of rock that is above a dip-slip fault plane

a. dip-slip fault

b. normal fault

c. reverse fault

d. strike-slip fault

e. thrust fault

-->  f. hanging wall

g. footwall

fault with a fault plane that is not vertical

-->  a. dip-slip fault

b. normal fault

c. reverse fault

d. strike-slip fault

e. thrust fault

f. hanging wall

g. footwall

fault with a vertical fault plane

a. dip-slip fault

b. normal fault

c. reverse fault

-->  d. strike-slip fault

e. thrust fault

f. hanging wall

g. footwall

reverse fault in which the fault plane is nearly horizontal

a. dip-slip fault

b. normal fault

c. reverse fault

d. strike-slip fault

-->  e. thrust fault

f. hanging wall

g. footwall

diagram questions

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Which letter represents the slip fault?

a. L

b. S

c. U

-->  d. T

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Identify the type of fault that the two plates remain on the same plane

a. A

b. L

-->  c. T

d. S

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Identify fault line

a. F

-->  b. S

c. Y

d. T

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Which label stands for the footwall?

a. T

-->  b. C

c. J

d. Y

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Identify the structure labeled J in the diagram

a. FOOTWALL

b. FAULT LINE

c. FAULT PLANE

-->  d. FAULT SCARP

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What part of the diagram represents a slope?

a. T

b. U

-->  c. J

d. F

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Which drawing represents a normal fault?

a. K

-->  b. F

c. P

d. W

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Which one i the normal fault in this diagram?

a. P

-->  b. F

c. S

d. K

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Identify the fault that generally exist near tectonic plate margins, in the broad disturbance zone.

a. S

-->  b. W

c. F

d. P

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Which label refers to the fault plane?

-->  a. S

b. NONE

c. P

d. E

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Which letter represents the Hypocenter?

a. NONE

-->  b. E

c. P

d. S

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Identify the hanging wall in the first image

a. W

b. N

c. L

-->  d. H

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In a (normal) Dip-Slip Fault situation, which letter label is used to illustrate a Hanging Wall?

a. L

b. N

-->  c. H

d. W

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What does the diagram labeled K represent?

a. A THRUST FAULT

-->  b. A STRIKE-SLIP FAULT

c. A NORMAL FAULT

d. A VOLCANIC FAULT

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Identify the strike-slip

a. U

-->  b. J

c. L

d. X

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Which letter represents normal?

a. U

b. J

-->  c. L

d. X

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Which kind of earth's fault results from shear stresses?

a. L

b. X

-->  c. J

d. U

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Which label refers to the strike-slip?

a. NONE

b. F

-->  c. S

d. R

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What is H?

a. HANGING WALL

b. FOOT WALL

-->  c. NORMAL FAULT

d. WALL

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Which label refers to the hanging wall block?

a. F

-->  b. X

c. K

d. P

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Which label shows the Footwall side?

a. T

b. H

c. K

-->  d. N

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Identify the letter that corresponds to the side of the tectonic plate that rise above the footwall side plate during compression stress.

a. N

b. K

c. H

-->  d. T

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Which label shows the Footwall?

a. X

b. L

-->  c. M

d. NONE

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What is shown for L?

a. FOOTWALL

b. HIGH WALL

-->  c. HANGING WALL

d. LOW WALL

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Which label refers to the Transform Plate Boundary?

-->  a. T

b. E

c. F

d. X

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What is the underground focus point of an earthquake?

-->  a. Hypocenter

b. Epicenter

c. Fault Plane

d. Center

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What is between the fault plane and the hypocenter?

-->  a. Epicenter

b. fault dome

c.  fault zone

d. normal fault

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What is the layer right below the crust?

a. Asthenosphere

b. Crust

c. Nothing

-->  d. Lithosphere

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Where do earth quakes happen?

-->  a. The crust

b. lithosphere

c. asthenosphere

d. earthquakes within the crust

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Which wall rises within a Reverse Dip-Slip Fault?

a. Neither

b. Both

-->  c. Hanging Wall

d. Footwall

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How many types of dip-slip fault are there?

-->  a. 2

b. 8

c. 4

d. 6

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In which type is the hanging wall below the footwall?

-->  a. Normal

b. Simple

c. Complicated

d. Reverse

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Which is the normal fault?

a. On top

-->  b. At the bottom

c. At the right

d. At the left

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How many types of faults are in the diagram?

a. 1

-->  b. 3

c. 4

d. 2

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How many types of slips are in this diagram?

a. 4

-->  b. 2

c. 3

d. 1

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How many trees are in the picture?

a. 4

b. 2

c. 6

-->  d. 3

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How many types of fault are shown in the diagram?

a. 1

-->  b. 3

c. 2

d. 4

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How many types of walls are in this diagram?

-->  a. 2

b. 1

c. 4

d. 3

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How many trees are shown?

a. 8

-->  b. 4

c. 6

d. 2

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What happens to tectonic plates after an earthquake?

a. They become uneven

b. They collide against each other

c. They move near the fault line

-->  d. They slide over each other

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What happens to the tectonic plates after an earthquake?

-->  a. They slide over each other along the fault line

b. The Tectonic plates fuses together

c. The tectonic plates move away

d. the tectonic plates stays the same

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How many tectonic plates are shown the illustration?

a. 1

b. 2

c. 3

-->  d. 4

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How many types of fault are there?

-->  a. 2

b. 4

c. 5

d. 3

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How many types of wall are there?

a. 1

b. 3

c. 4

-->  d. 2

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What happens when there is an increase in the compressional stress?

a. footwall side will go down

-->  b. hanging wall side will go up

c. wall side will crack

d. wall side will shrink

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How many types of faults are there in this picture?

-->  a. 3

b. 7

c. 5

d. 4

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How many types of wall are shown below?

a. 3

b. 1

c. 4

-->  d. 2

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What is the block of rock that lies on the underside of an inclined fault or of a mineral deposit?

a. Rock Bottom

b. Hanging Wall

c. Crust

-->  d. Footwall

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What type of stress is described as stretching and thinning?

-->  a. Extensional stress

b. Shear stress

c. Compressional stress

d. Divergent Plate stress

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How many types of movement are shown in the diagram?

a. 2

-->  b. 3

c. 4

d. 1

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How many types of faults are shown in this diagram?

a. 4

b. 1

-->  c. 3

d. 2

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How many types of fault are there?

-->  a. 2

b. 3

c. 5

d. 4

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What kind of force acts on a strike-slip fault?

a. Strong force

b. Compression force

c. Tension force

-->  d. Shearing force

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Which type of fault is caused by forces compressing together?

a. Strike-Slip Fault

b. Standard Fault

-->  c. Reverse Fault

d. Normal Fault

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How many types of fault are shown in the diagram?

a. 3

-->  b. 4

c. 2

d. 1

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How many types of faults can occur?

-->  a. 3

b. 4

c. 5

d. 2

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In this diagram of stress in earths crust, what causes reverse fault?

a. Tension Forces

b. Fault Line

-->  c. Compression Forces

d. Shearing Forces

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If the hanging wall drops down relative to the foot wall it is known as which of the following?

a. Right-lateral fault

b. Left-lateral fault

-->  c. Normal fault

d. Reverse fault

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In which type of fault does the hanging wall slide above the foot wall?

a. Right-lateral fault

b. Left-lateral fault

c. Normal fault

-->  d. Reverse fault

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How many types of faults are shown in the diagram?

a. 2

b. 3

c. 1

-->  d. 5

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How many types of lateral faults are there?

-->  a. 2

b. 5

c. 1

d. 3

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Which fault is where the hanging wall moves down and the foot wall moves up?

-->  a. normal fault

b. reverse fault

c. active flexures

d. right-lateral fault

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From the diagram, how many types of fault are there?

a. 2

-->  b. 3

c. 1

d. 4

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List the different types of stresses that change rock.

a. Red layers of shale are flakier and form slopes.

-->  b. Confining stress happens as weight of all the overlying rock pushes down on a deeply buried rock. Compression stress squeezes rocks together.  Tension stress pulls rocks apart.

c. This is magnificently displayed around the southwestern United States.

d.  Layers of different types of rocks are ex- posed in this photo from Grand Staircase- Escalante National Monument. White lay- ers of limestone are hard and form cliffs.

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How many dip slip faults are shown in the diagram?

a. 4

-->  b. 2

c. 3

d. 1

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How many types of fault are there?

a. 1

b. 3

c. 2

-->  d. 4

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Which occurs in areas undergoing compression (squishing)?

a. Strike-slip Fault

b. Normal Fault

c. Direction of Force

-->  d. Reverse Fault

question_image

Which number is the normal fault?

a. 4

-->  b. 1

c. 3

d. 2

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Which type of fault causes the hanging-wall block moves down with respect to the foot wall block?

a. Reverse and transverse

-->  b. Normal

c. Transverse

d. Reverse

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How many types of faults are shown in the diagram?

a. 1

b. 2

-->  c. 3

d. 4

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What type of faulting compresses rather than extends?

a. Strike-slip faulting

b. Hanging wall faulting

c. Normal faulting

-->  d. Reverse and thrust faulting

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What is the process in which rocks drop down relative to rocks across the fault?

-->  a. Normal Faulting

b. Compression

c. Reverse and trust faulting

d. Strike-slip faulting

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What is occurring in the strike-slip fault in the diagram?

a. The fracture is diagonal and the ground shifts horizontally

b. The fracture is horizontal and one plate slips under the other

c. The fracture is vertical and one plate slips under the other

-->  d. The fracture is vertical and the ground shifts horizontally

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How many types of fault are shown in the diagram?

a. 1

-->  b. 3

c. 4

d. 2

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How many types of faults are there in this picture?

a. 6

b. 5

c. 4

-->  d. 3

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Which of the following is not a type of geological fault?

a. strike-slip

b. normal

c. reverse

-->  d. harsh

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What is the lowest lying area of an escarpment?

a. Fault plane

b. Fault scarp

c. Upthrown block

-->  d. Downthrown block

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What is directly between upthrown block and downthrown block?

-->  a. Fault line

b. Foot wall

c. Fault scarp

d. Haning wall

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Where is the hanging wall located?

a. Under the footwall.

-->  b. Above the fault.

c. Beside the fault.

d. Under the fault.

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How many types of wall are shown below?

a. 5

b. 4

-->  c. 2

d. 3

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Which picture represents a Right Lateral Strike-Slip Fault

a. Middle

-->  b. Bottom Left

c. Top Left

d. Top Right

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How many types of faults are shown in this diagram?

a. 3

b. 4

-->  c. 5

d. 2

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How many types of faults are there according to the diagram?

a. 6

b. 4

-->  c. 5

d. 7

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What is it called if the fault plane terminates before it reaches the Earth's surface?

-->  a. Reverse Fault

b. Normal Fault

c. Left Lateral Strike-Slip Fault

d. Blind Reverse Fault

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How many types of faults are there?

-->  a. 3

b. 2

c. 1

d. 4

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Define the compression

a. hanging wall side

b. compressional stress

c. footwall side

-->  d. thrust or reverse fault

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What is the rocky mountains?

a. footwall

b. underwall

c. overwall

-->  d. hanging wall

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Identify the normal fault

a. S

b. B

c. R

-->  d. F

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Identify the hanging wall block

a. P

-->  b. X

c. F

d. K