ASBOG Practice Exam

What is the angle range for a thrust fault?

1. 0 to 30 degrees

2. 0 to 45 degrees

3. 30 to 60 degrees

4. 45 to 90 degrees

The correct answer is: 0 to 45 degrees

Thrust faults are characterized by the angle at which one block of the Earth's crust is forced over another. Specifically, the angle of the fault plane in a thrust fault typically ranges from 0 to 30 degrees from the horizontal. This low-angle nature is a defining feature of thrust faults, allowing them to accommodate horizontal compressive stresses that typically occur in orogenic (mountain-building) environments. While some sources might indicate that thrust faulting can occur at angles slightly above 30 degrees under certain conditions, the standard classification maintains that thrust faults are primarily recognized in this lower angle range due to their common association with convergent tectonic plate boundaries. Higher angles, such as those found in other types of faults (like reverse or strike-slip faults), would not be classified as thrust faults. Understanding this concept is crucial in structural geology and tectonics, as it relates to how stress is transferred through the Earth's crust and how geological features such as mountain ranges and fold systems are formed.