Faults

Question 1

What is the dip?

Answer 1

Maximum angle of slope from the horizontal

Question 2

What is the strike?

Answer 2

Bearing of a horizontal line on a bedding plane. It is at right angles to the bedding plane

Question 3

What could you use to figure out the dip?

Answer 3

A marble and protractor, the marble will roll down the steepest angle
A compass-clinometer

Question 4

What are features of a Normal fault?

Answer 4

The hanging wall is the downthrown and the footwall is the upthrown

Question 5

What kind of stress causes a normal fault?

Answer 5

Extensional

Question 6

What is a low angle normal fault called?

Answer 6

A lag fault

Question 7

What are features of a reverse fault?

Answer 7

The hanging wall is the upthrown and the footwall is the downthrown

Question 8

What kind of stress causes a reverse fault?

Answer 8

Compressional

Question 9

What is a low angle reverse fault called?

Answer 9

A thrust fault

Question 10

What degree from the horizontal constitutes a thrust fault?

Answer 10

<15°

Question 11

How do you tell if a stroke slip fault is dextral or sinister?

Answer 11

Imagine you are standing facing the fault. If the bed opposite has moved right it’s dextral, left it’s sinister

Question 12

What are the features of a Horst and Graben structure?

Answer 12

A series of normal faults in alternating directions, with a high up block called the horst and a lower down trench called the Graben

Question 13

What is a fault plane?

Answer 13

The surface along which the rock breaks

Question 14

What are features of step faults?

Answer 14

A series of normal faults in the same direction

Question 15

What is the fault dip measured from?

Answer 15

The horizontal

Question 16

How do you find the displacement of a fault?

Answer 16

It’s the distance along the fault plane, between a bed on either side of a fault

Question 17

How do you find the throw of a fault?

Answer 17

Take the vertical distance between the bed on either side of the fault plane

Question 18

What are some features of fault planes?

Answer 18

• fault breccia
• mylonites
• slickensides
• fault gouge

Question 19

What are the properties of a fault breccia?

Answer 19

• coursely grained (>2mm)
• poorly sorted
• angular

Question 20

How are fault breccia formed?

Answer 20

By cataclaysis - Friction between blocks as they pass one another, breaking off pieces of rock (and some grinding and attrition)

Question 21

How is mylonite formed?

Answer 21

Through extreme cataclaysis, where fault gouge is dynamically metamorphosed. Its more common in thrust faults

Question 22

What are slickensides?

Answer 22

Scratches (striations) and polishing on the surface of the fault plane. They are used to indicate the direction of relative movement, but can be formed by mineral growth.

Question 23

How can slickensides show the relative movement?

Answer 23

The orientation of the striations and which direction the rock feels smooth

Question 24

What is fault gouge?

Answer 24

Very fine particles of rock that are created by the grinding of rock along the fault plane. They can be dynamically metamorphosed into mylonite