Here's why:

* Strike-slip faults are characterized by horizontal movement of rocks on either side of the fault.

* The movement can be in opposite directions (e.g., one side moves right, the other side moves left), which is called a right-lateral strike-slip fault.

* Or, the movement can be in the same direction but at different rates, which is called a left-lateral strike-slip fault.

Example: The San Andreas Fault in California is a right-lateral strike-slip fault. The Pacific Plate is moving northward relative to the North American Plate, causing the two plates to slide past each other horizontally.