Footwall Meaning
The deposits of minerals have different shapes, which depend on how they were deposited. The most common shape of mineral deposition is mostly the tabular form. The mineral deposit in the form of a filling is mostly situated in layers of rock that are parallelly placed. The orientation of this ore body is to be marked by its dip (this is the angle which it makes with the horizontal structure) and this strike (the position which it takes in regard to the four points of the compass). The Rock that is lying above the ore body is known as the hanging wall and the rock which is lying below the ore body is called the footwall.
Analysis of Footwall Morphology
Under the U.S Geological Survey National Elevation Dataset that is elevation data, we will analyze footwall morphology along each fault, with a horizon of 30 m resolution. The data is very much coarse and have particularly the accurate delineation of the catchments draining of the Stone Creek and Sweetwater footwalls. Higher‐resolution (that is 10 m) data is utilized only as a part of the study area, hence we use the same 30 m data to make comparison results from all the different kinds of footwalls. For each of these faults, we need to extract the footwall catchments which is >0.05 km2 in area and the drain across the map that is traced is the active fault (the darker shaded areas).
In the first attempt at quantifying the footwall morphology, we are required to calculate the simplest possible measures of these catchments that is their area, relief, and their mean slope.
To assess further along with the strike variations in footwall relief, we need to project the extracted footwall catchments which are onto a fault parallel to the profile. At each of the positions along the profile we then calculate the maximum, mean, and minimum elevations in the fault‐normal direction. The footwall relief at each point is the difference between the maximum elevations and minimum elevations. This method is quite sensitive to the small‐scale variations in which the plan‐view catchment shape is not the true measure of an individual catchment which has relief because of the catchments that got widened away from the fault. In these places, the swath is not exact to the fault parallel. However, this method allows us to derive a continuous type footwall relief profile and then eliminate the issues that are inherent in the arbitrary selection along with the striking profile. As a check, we also need to calculate the relief in the individual catchments as a function of the outlet position along strike; and the overall patterns and length scales that are very much similar to those which are derived from this profiling method.
For the suspect that relief in these tectonically active footwalls may be strengthened the limited, implying a relationship between the topographic slope and the relief, we also are required to calculate the average catchment slopes within these extracted regions.
We then determine the mean topographic slope for each of the catchments, using the slope values which are measured over a 3 × 3 cell (90 × 90 m) size window. The slope will be estimated using the 30 m resolution digital elevation model which will significantly underestimate the true meter‐scale that the slope values, while these estimates and will provide a useful means to compare the slopes which are averaged over the scale of individual hillslopes, that is present along the strike and between the different footwalls.
Catchment Patterns
For both that is the Stone Creek and the Sweetwater faults, there are cuts across a smooth and low‐relief surface which developed on the Archean gneiss. It is being tilted to the southeast by Miocene which is faulting of the Ruby Range block. These faults define the small range fronts which are quite steep and is linear near the fault and the strike centers and they become more diffused and difficult to separate from the inherited topography that is on the Ruby Range block near the fault tips. Both these footwalls represent asymmetric map‐view catchment patterns where the smallest catchments may occur near the fault strike center, which we need to infer the displacement maxima. The Catchment areas also increase and progressively advance towards the fault tips. The location of the smallest catchments near this strike center is close to the inferred displacement maximum, which is somewhat counterintuitive. Everything being the same, higher displacements near these faults in the midpoint should also lead to higher rates of footwall incision, and therefore larger the structure, the more widely spaced catchments will be. Both the footwalls are then composed only with Archean gneiss. This is done so that lithology swill is not a significant control on the catchment size.
The Blacktail and the Red Rock footwalls also show a greater variation in the along‐strike distribution of catchment areas which is single‐segmented. The largest catchments, which are the Beaver head River and the Blacktail Deer Creek located in the Blacktail footwall and the Big Sheep and Little Sheep Creeks which is located in the Red Rock footwall, are the antecedent to these faults’ structures. They are based on their regional extent and their continuity across several footwall blocks. The catchments which are being developed in response to this fault displacement have no distinct pattern that emerges. We are required to interpret this as to take due action in part of the fault tip propagation into these areas of significant and pre-faulting topography system.
FAQs on Footwall
1. What is a footwall in geography?
In geology, a footwall is the block of rock that lies beneath an inclined fault plane. A simple way to remember this is to imagine yourself standing on the fault line; the block of rock under your feet would be the footwall. It serves as a fundamental reference point for analysing the movement and type of a geological fault.
2. What is the main difference between a footwall and a hanging wall?
The primary difference between a footwall and a hanging wall is their position relative to the fault plane. The footwall is the block of rock situated below the fault, whereas the hanging wall is the block of rock located above it. This distinction is crucial for classifying different types of faults, such as normal faults, where the hanging wall moves down, and reverse faults, where the hanging wall moves up.
3. How can you identify a footwall in a diagram of a fault?
To identify a footwall in a geological diagram, first locate the inclined line representing the fault plane. The entire block of rock shown underneath this tilted line is the footwall. Conversely, the block resting on top of the fault plane is the hanging wall. In diagrams illustrating normal faults, the footwall is the block that has moved up relative to the hanging wall.
4. Why is understanding the footwall important in real-world applications like mining?
Understanding the footwall is critical for both geological analysis and practical applications like mining and engineering. Its importance is seen in several areas:
- Fault Classification: The movement of the footwall relative to the hanging wall helps geologists determine if a fault is normal, reverse, or thrust, which in turn indicates the type of tectonic stress an area is under.
- Mining Stability: In mining operations, valuable mineral ores are often found along fault zones. Miners typically use the footwall as the stable foundation for constructing tunnels (footwall drives) because it is the underlying, more stationary block, ensuring structural safety.
- Resource Exploration: Geologists search for 'footwall traps' in petroleum exploration, as these geological structures can hold significant oil and natural gas reserves.
5. How does the relative movement of a footwall differ in a normal fault versus a reverse fault?
The apparent movement of the footwall is always described relative to the hanging wall. In a normal fault, which is caused by tensional stress pulling rocks apart, the hanging wall drops down. This makes the footwall appear to have moved upwards. In a reverse fault, which is caused by compressional stress pushing rocks together, the hanging wall is forced up and over the footwall, making the footwall appear to have moved downwards.
6. Can a footwall exist without a hanging wall?
No, in the context of inclined faults (like normal or reverse faults), a footwall cannot exist without a hanging wall. The terms are relational and codependent; one is defined by its position relative to the other across a fault plane. You can only identify a footwall (the block below) if there is a corresponding hanging wall (the block above). These terms are generally not applied to vertical faults where the blocks slide past each other horizontally.
7. What are some other key geological terms related to a footwall and a fault?
Besides the footwall and hanging wall, a complete understanding of a fault involves other key components:
- Fault Plane: This is the actual surface or fracture in the rock along which movement has occurred.
- Fault Scarp: The exposed part of the fault plane on the Earth's surface, often appearing as a cliff or a step in the landscape.
- Dip: The angle at which the fault plane is tilted from the horizontal plane.
- Strike: The compass direction of the line formed by the intersection of the fault plane with a horizontal surface.
