Final answer:
Detachment faults are normal faults that flatten out at depth, detaching the upper crust from the lower option b is answer
Step-by-step explanation:
The faults that are normal faults and flatten out to about horizontal deep in the Earth are referred to as detachment faults. These detachment faults are a particular type of normal fault where the hanging wall moves down relative to the footwall, and the fault plane flattens with depth. The term detachment is used because these faults detach the upper part of the crust from the lower part.
In the context of plate tectonics, faulting is generally associated with different types of plate boundaries and the movements that occur there. Normal faults, like detachments, are typically formed in areas of crustal extension, whereas reverse faults and thrust faults occur in areas of compression. These faults play a crucial role in shaping the Earth's surface and contribute to phenomena like earthquake activity. option b is answer