Question

The rake (pitch) of slickenslides exposed on a moderately dipping fault plane is the angle between

• A. the magnetic north and strike of the fault plane measured on a horizontal surface
• B. the strike of the fault plane and the slickenslides measured on the fault plane
• C. the strike of the fault plane and the slickenslides measured on a vertical plane
• D. the trend and the plunge directions of slickenslides measured on the fault plane

Hint:

The rake is always measured on the fault plane and refers to the angle between the slickenslide direction and the strike of the fault.

Answer 1

The Correct Option is B

Step 1: Understanding rake (pitch).
The rake (or pitch) of a slickenslide is the angle between the line of the slickenslide (the striations or grooves on the fault surface) and the horizontal plane of the fault. It is a measure of the direction and amount of slip along the fault.

Step 2: Analyzing the definition of slickenslides.
Slickenslides are features on fault planes caused by movement along the fault. The pitch or rake measures how the slickenslide line deviates from the horizontal plane.

Step 3: Analyzing the magnetic north and strike of the fault plane.
Option (A) suggests using magnetic north, which is unrelated to the rake of the slickenslides, as rake is measured relative to the fault plane itself. Thus, this is not the correct choice.

Step 4: Analyzing the strike of the fault plane and the slickenslides.
Option (B) correctly states that the rake is the angle between the strike of the fault plane and the slickenslide measurements on the fault plane. This directly measures the deviation of the slip direction from the horizontal.

Step 5: Analyzing the strike and slickenslides on a vertical plane.
Option (C) incorrectly suggests measuring the slickenslides on a vertical plane. The rake is measured on the fault plane, not a vertical plane. Hence, this option is not correct.

Step 6: Analyzing the trend and plunge directions of slickenslides.
Option (D) involves the trend and plunge directions, which are related to the orientation of lines in three-dimensional space but are not relevant to the measurement of rake, which involves the fault plane itself.

Step 7: Conclusion.
Therefore, the correct answer is option (B), where the rake is the angle between the strike of the fault plane and the slickenslides measured directly on the fault plane.
\[ \boxed{\text{The strike of the fault plane and the slickenslides measured on the fault plane}} \]