Which of the following is NOT one of the three types of faults?

The identification of the three primary types of faults in geology is fundamental in understanding how the Earth's lithosphere behaves during tectonic activity. The three main types of faults are normal faults, reverse faults, and strike-slip faults.

Normal faults occur where the crust is being extended. This process typically happens in regions undergoing tension, where one block of the Earth's crust (the hanging wall) moves down relative to another block (the footwall). Reverse faults, on the other hand, are associated with compressional forces where the hanging wall moves up relative to the footwall. Strike-slip faults involve lateral movement where two blocks slide past one another horizontally.

The option that does not belong to this standard classification of fault types is the diagonal fault, which is not recognized as a specific type of fault in geological literature. Hence, this selection reinforces the understanding of fault mechanisms within the framework of plate tectonics, indicating that the understanding of fault types is crucial for analyzing geological structures and understanding seismic behavior.