ASBOG Practice Exam

Which of the following correctly depicts a fault where the angle is less than 90 degrees?

1. Normal fault

2. Reverse fault

3. Thrust fault

4. Strike-slip fault

The correct answer is: Reverse fault

A reverse fault is characterized by a compressional movement where one block of rock is pushed up over another block along a steep fault plane. In reverse faults, the angle of the fault is generally steeper than 30 degrees but less than 90 degrees, allowing for the upward movement of rock masses. The criteria for designating a fault as a reverse fault hinge on the angle of the fault plane related to the direction of stress. This type of fault plays a vital role in the formation of mountain ranges where compressive forces are prevalent. In contrast, normal faults occur with a dip of more than 45 degrees, which is the result of extensional forces that pull apart the earth’s crust. Thrust faults are similar to reverse faults but have a shallower angle, typically less than 30 degrees, which tends to be more gradual and results in horizontal displacement. Strike-slip faults, on the other hand, are characterized by lateral movement along a horizontal plane with no significant vertical displacement, making the concept of angle less relevant.