How might a geologist use relative dating to determine when the fault occured?

Answer 1

The Law of Cross-Cutting Relationships would be used here. If a fault cuts across a rock unit, it is younger than that rock unit. If a fault cuts across a series of rocks, but suddenly stops at a rock unit, then that rock unit which the fault stops at is younger than the fault. So let's say the order of rocks (from top to bottom), is A B C D. If the fault cuts across B C and D, but not A, then the age of the fault is sometime between A and B. If you know the absolute ages of A and B (let's say, rock A is 100 million years old and rock B is 200 million years old), then the age of the faulting is between 100 and 200 million years ago.

Answer 2

A geologist can use relative dating techniques such as the principle of cross-cutting relationships to determine when a fault occurred. By observing which rock layers are cut by the fault and the sequence of events, they can infer the relative timing of the fault formation compared to the surrounding rocks. Additionally, studying the age of the rocks on either side of the fault can provide further constraints on the timing of faulting.