Question

The three types of faults are normal faults, reverse faults, and strike-slip faults. Draw each type of fault including arrows that show which way the rocks move.

Short answer

Normal faults move downwards, reverse faults upwards, and strike-slip faults horizontally.

Step-by-step solution

Illustrating the Normal Fault

In a normal fault, the hanging wall moves downward relative to the footwall. This occurs due to tensional forces which pull the crust apart. To illustrate this, draw two blocks of rock: the block on the left represents the footwall, and the block on the right is the hanging wall. Add arrows pointing downward on the hanging wall and upward on the footwall to show the direction of movement.

Illustrating the Reverse Fault

A reverse fault has the hanging wall moving upwards relative to the footwall due to compressional forces that squeeze the crust. Draw two blocks again: the left block is the footwall, and the right block is the hanging wall. On this diagram, place arrows pointing upward on the hanging wall and downward on the footwall to indicate the direction of the force.

Illustrating the Strike-Slip Fault

In a strike-slip fault, the blocks move horizontally past each other. This usually happens due to lateral shear forces. Draw two blocks adjacent to each other, and add arrows on the surface pointing in opposite horizontal directions—one block rightward and the other block leftward—to represent the motion of the rocks.

Key concepts

Normal Fault

A normal fault is a type of fault where the hanging wall moves downward relative to the footwall. This movement occurs because of tensional forces that stretch or pull apart the Earth’s crust. Picture the crust as a rubber band that snaps back when it stretches too far. When illustrating a normal fault in a geological diagram, you would sketch two blocks of rock. The left block represents the footwall, and the right block represents the hanging wall. By showing arrows pointing downward on the hanging wall and upward on the footwall, you can see the direction the rocks move during this type of faulting. This downward movement makes valleys or gaps in the Earth's crust as it stretches apart.

Reverse Fault

In a reverse fault, the opposite occurs compared to a normal fault. Here, the hanging wall moves up relative to the footwall due to compressional forces, which push the crust together. Imagine squeezing a sponge tightly—the pressure forces parts of it upward. When illustrating a reverse fault, draw two adjacent blocks where the left is the footwall and the right is the hanging wall. Add arrows pointing upward on the hanging wall and downward on the footwall in the geological diagram. These arrows show the compressional force at work, demonstrating how the Earth's layers are squashed together to form mountains or ridges.

Strike-Slip Fault

A strike-slip fault features a horizontal movement where two blocks slide past each other. This is largely due to lateral shear forces, which push blocks in opposite directions sideways. Think of two books on a table that glide past one another when you slide them sideways. To illustrate a strike-slip fault, draw the blocks in parallel but with one moving to the right and the other moving to the left. Adding arrows that point in these opposite horizontal directions makes it easy to see how the blocks are shifting. The classic example is the San Andreas Fault in California, where such sideways movement often results in the release of significant seismic energy.

Earthquake Forces

Earthquake forces are responsible for the movements seen in different types of faults such as normal, reverse, and strike-slip faults. These forces include tensional forces (stretching the crust), compressional forces (squeezing the crust), and shear forces (sliding the crust laterally). Each type of force leads to different fault behaviors and subsequently different geological features. For example, tensional forces can create a rift valley, while compressional forces can lead to the formation of mountain ranges. Understanding these forces is crucial for predicting earthquake activity and developing engineering solutions to mitigate earthquake damage.

Geological Diagrams

Geological diagrams are visual representations that help us understand Earth’s internal structures and processes. These diagrams simplify complex geological phenomena, like fault movements, so that we can study them more precisely. When creating or interpreting geological diagrams, it's important to include key elements such as the orientation and type of faults, the direction of forces, and any resulting landscape features. For students learning about faults, diagrams serve as an essential tool to grasp how faults operate and show the immediate consequences of tectonic movements. They also offer a window into past Earth movements, allowing geologists to make educated guesses about future tectonic activity.