Question

When the rock above the fault surface moves down relative to the rock below the fault surface, what kind of fault forms? A) normal C) reverse B) strike-slip D) shear

Short answer

It forms a normal fault (option A).

Step-by-step solution

Identify the Movement

First, identify the direction of movement of the rocks in relation to the fault surface. In this problem, the rock above the fault surface is moving down relative to the rock below it.

Recognize the Fault Type

There are specific fault types associated with certain movements. In a normal fault, the rock above the fault surface (hanging wall) moves downward relative to the rock below (footwall). This movement is typically due to extensional forces.

Compare with Given Options

From the given options, identify which type corresponds to the described movement. Option A describes a normal fault, where the hanging wall moves down. - A) Normal - C) Reverse - B) Strike-slip - D) Shear

Confirm the Answer

Based on the understanding from the previous steps, when the rock above the fault surface moves down relative to the rock below, it is indicative of a normal fault. Therefore, the correct answer is option A.

Key concepts

Normal Fault

When discussing different types of faults, the normal fault stands out as a fundamental geological formation. It occurs when extensional forces within the Earth's crust cause a section of rock, known as the hanging wall, to move downward in relation to the section beneath it, the footwall. This movement results in a tilted fault plane, which is a clear identifier of a normal fault.
A few key points about normal faults include:

• They are generally associated with divergent boundary settings where the Earth's tectonic plates are moving apart.
• Movement along a normal fault is vertical, as depicted by the downward slipping of the hanging wall.
• Normal faults can lead to the formation of features such as rift valleys.

Fault Movement

Understanding fault movement is crucial in identifying and differentiating between various types of faults. In a normal fault, the movement is characterized by a vertical drop of the hanging wall, compared to other faults which might exhibit lateral or horizontal movements. This displacement is typically driven by tensional forces that stretch the crust apart, reducing the overall stress level within the crust.
Key characteristics of fault movement in normal faults:

• They exhibit a downward slip along the fault plane.
• Such movements often result in the lengthening of the crust in the region where they occur.
• Unlike reverse or thrust faults, the stresses involved in normal faults pull the two sides of the fault away from each other.

Geological Processes

Geological processes refer to the dynamic forces and events that shape the Earth's surface and structure. Normal faults are a significant component of these processes, particularly in areas where tectonic plates are diverging or stretching. Some important aspects of geological processes involving faults are:

• They play a critical role in the recycling and creation of new crust material.
• Faults form natural pathways for the movement of groundwater, influencing the hydrology of regions.
• The movement along faults is also a major cause of earthquakes, especially in regions with active tectonics.

These processes not only drive the physical formation and alteration of the Earth's surface but also affect the ecosystems and human activities associated with these regions.