Question

A northerly dipping fault (F-F) has displaced beds P, Q and R. The thickness of the beds across the fault is same. Identify the fault type(s). 

• A. Dextral fault
• B. Reverse fault
• C. Normal fault
• D. Sinistral fault

Hint:

Normal faults are common in regions experiencing extensional tectonic forces, where the crust is being pulled apart.

Answer 1

The Correct Option is B, D

Analyzing the fault geometry:

Given information:

• Northerly dipping fault (F-F)
• Beds P, Q, R are displaced
• Thickness of beds is constant across the fault
• Map view shows bed patterns on both sides

Observations from the map:

1. The fault dips northward, making the north block the hanging wall and the south block the footwall
2. Beds P, Q, R appear on both blocks
3. The beds strike obliquely to the fault trace

Determining vertical displacement:

Examining the stratigraphic sequence across the fault:

• The hanging wall (north block) exposes stratigraphically older or higher structural levels
• This indicates the hanging wall has moved upward relative to the footwall
• Vertical component: Reverse fault

Determining lateral displacement:

Analyzing the horizontal offset of beds:

• Tracing any bed (e.g., bed Q) across the fault from south to north
• Standing on the south block and looking north across the fault, the corresponding bed on the north block is displaced to the left (west)
• This indicates left-lateral (sinistral) displacement
• Horizontal component: Sinistral fault

Conclusion:

The fault exhibits oblique-slip motion with two components:

• Reverse fault component (dip-slip): hanging wall moved up
• Sinistral fault component (strike-slip): left-lateral offset

Answer: (B) Reverse fault and (D) Sinistral fault