Video Transcript
A geologist observes a fault in the field. The extract from their field notebook describing it reads, “The fault has a hanging
wall that has moved downward relative to the footwall and has a steeply dipping
fault plane.” What type of fault did the geologist see? (A) A reverse fault, (B) a thrust fault, (C) a normal fault, (D) a strike-slip
fault.
Let’s review each type of fault in order to determine which type the geologist
described in their field notebook.
Reverse faults are a result of compressional forces. In a reverse fault, the hanging wall has moved upward relative to the footwall along
the fault plane. Thrust faults, like reverse faults, form due to compressional stresses. The motion is the same as a reverse fault, but the fault plane, shown in pink, is
much more horizontally inclined.
Normal faults are the result of tensional forces. Due to the tensional forces, the hanging wall moves downward relative to the
footwall.
Strike-slip faults occur where shear forces result in lateral displacement of the
crust. The fault plane is vertical, and the movement along the fault plane is
horizontal.
Now that we′ve looked at the different types of faults, let′s return to the
question. The geologist noted that the fault plane was steeply dipping and the hanging wall
moved downward relative to the footwall. This fits the description of a normal fault. So, the type of fault the geologist saw was a normal fault.
