Faults are fractures in the Earth's crust where there has been significant displacement. They are classified based on the direction of relative movement between the two blocks of rock on either side of the fault plane. These blocks are called the hanging wall (the block above the fault plane) and the footwall (the block below the fault plane).
Step 1: Understanding the Question:
The question describes a specific type of fault movement—the hanging wall moving down with respect to the footwall—and asks for the name of this fault type.
Step 2: Detailed Explanation:
Let's examine the different types of faults based on movement:
Normal fault: The hanging wall moves downward relative to the footwall. This is caused by tensional forces (stretching or pulling the crust apart).
Reverse fault: The hanging wall moves upward relative to the footwall. This is caused by compressional forces (squeezing the crust).
Thrust fault: This is a special type of reverse fault with a low-angle fault plane (typically less than 45 degrees).
Strike-slip fault: The movement is horizontal (sideways), with little to no vertical motion.
The movement described in the question is the defining characteristic of a normal fault.
Step 3: Final Answer:
A fault where the hanging wall moves downward relative to the footwall is a Normal fault.