Question

If a dextral strike-slip fault system has a right step-over, which one of the following features will develop?

• A. Zone of reverse fault
• B. Releasing bend
• C. Restraining bend
• D. Contractional duplex

Hint:

Recall the Salton Trough example: a right step in a dextral fault pulls the ground apart rather than squeezing it.

Answer 1

The Correct Option is B

Step 1: Understanding the Question.
In a strike-slip fault system, individual fault segments are often offset from one another rather than forming one continuous line. This offset, called a step-over, can be a left step or a right step depending on how the second segment is shifted relative to the first. The question asks what feature forms at a right step-over in a dextral, that is right-lateral, fault system.

Step 2: Key Concept.
Whether a step-over opens up under extension or squeezes together under compression depends on both the sense of slip and the stepping direction. For a dextral fault, a right step-over pulls the two overlapping fault segments apart, creating a zone of local extension called a releasing bend, commonly marked by a pull-apart basin. A left step-over in a dextral fault instead pushes the segments together, creating a restraining bend with local compression and uplift. For a sinistral fault the relationship reverses, a right step becomes restraining and a left step becomes releasing. The Salton Trough in California is a well known pull-apart basin formed at a right step-over along the dextral San Andreas fault system.

Step 3: Detailed Explanation.

(A) Zone of reverse fault: Reverse faulting is a compressional feature, more typical of a restraining bend, not the extensional setting produced by a right step in a dextral system.

(B) Releasing bend: This is the extensional feature produced when a right-lateral fault steps to the right, since the two overlapping segments are pulled apart, thinning the crust between them and often forming a pull-apart basin.

(C) Restraining bend: This compressional feature forms at a left step-over in a dextral fault, not a right step-over.

(D) Contractional duplex: A contractional duplex, with imbricate thrust slices between the fault strands, also belongs to a restraining, not releasing, setting.

Step 4: Final Answer.
A right step-over in a dextral strike-slip fault system pulls the fault segments apart and produces local extension, so the feature that develops is
\[ \boxed{\text{Releasing bend}} \]