Chapter 10, Problem 1RQ

To determine

The comparison among normal, reverse, and strike-slip faults.

Answer to Problem 1RQ

Normal faults occur when the hanging wall moves down with respect to the footwall along a fault plane and are commonly found related to crustal stretching. Reverse faults, associated with the crustal compression, are characterized by the upward movement of the hanging wall relative to the footwall. Unlike the normal and reverse faults, the strike slip faults have no upward or downward movement of any of the blocks, rather one block slides past the other, creating offsets.

Explanation of Solution

The fractures along which a crustal block slips past another block are referred as faults. The blocks taking part in this slipping movement can be given two different names depending on their position relative to the fault plane-the hanging wall and the footwall. If observed in cross-section, drawing a vertical line that meets the fault plane can explain the difference amid a hanging wall and a footwall.

Hanging wall is the material or rock body lying on the opposite side of the fault below the intersection of the vertical line and the fault. Footwall represents the material or rock body lying on one side of the fault above the intersection of the vertical line and the fault. On account of the relative movement of the hanging wall and footwall, the faults are generally classified into three namely the normal faults, reverse faults, and strike slip faults.

In a normal fault, the hanging wall moves down relative to the footwall along the fault plane. Normal faults are usually associated with the stretching of the crust, as observed in a continental rift. On the other hand, a reverse fault will have an upward movement of the hanging wall with respect to the footwall along the fault plane. Such faults are generated in regions like a collisional mountain belt where crustal compression takes place. Normal and reverse faults take place on planes, which orient themselves at an angle between horizontal and vertical.

The fault movement in which a block “slides past” another block, with no up or down displacement as in normal and reverse faults, is known as a strike-slip fault. These faults occur on comparatively vertical planes. Strike-slip faults can offset streams and ridges sideward. Offset comprises the blocks laterally slipping past each other, along the intersection amid the ground surface and fault plane, which is the line of strike.