# Normal or Reverse? Looking at the two types of vertical displacement in dip-slip faults using the hanging wall method.

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Normal or Reverse? Looking at the two types of vertical displacement in dip-slip faults using the hanging wall method

Terminology An easy method to decide what sort of dip-slip fault we have uses the old mining terms of: Hanging wall and Footwall

The footwall is always underneath the fault fault The hanging wall is always on top of the fault These names do not need us to know which side has moved up or down or if a tension or compression has occurred Hanging wall Footwall

Hanging Wall Footwall 1 km We apply this to the fault we looked at in the introduction to faults. Hanging wall Footwall fault The block above the fault plane is the hanging wall, and the block below the fault is the footwall.

Draw arrows to show the relative movement on either side of the fault. ⇃ ↾ Hanging wall Footwall

T his makes F N ! U Is the footwall the upthrow side or downthrow side of the fault? Footwall Hanging wall The arrow points up, it must be the upthrow side. Upthrow F ootwall This is a normal fault. U pthrow N ormal ⇃ ↾ F U N

Normal faults are caused by a pulling apart motion (tension). Hanging wall Upthrow Footwall ⇃ ↾

Another example

1 km Two interpreted horizons. Two faults. The block above the fault plane is the hanging wall, and the block below the fault is the footwall. Look at the fault in the NW. Hanging wall Footwall

1 km Hanging wall Footwall Draw arrows to show the relative movement on either side of the fault. ⇃ ↾

1 km Hanging wall Footwall Is the footwall the upthrow side or downthrow side of the fault? The arrow points down, it must be the downthrow side. F ootwall D ownthrow T his does not make FUN! This is a reverse fault. ⇃ ↾

1 km Hanging wall Footwall Reverse faults are caused by a pushing together motion (compression). ⇃ ↾

1 km Try the other fault. The block above the fault plane is the hanging wall, and the block below the fault is the footwall. Hanging wall Footwall

1 km Hanging wall Footwall Draw arrows to show the relative movement on either side of the fault. ↿ ⇂

1 km Hanging wall Footwall ↿ ⇂ Is the footwall the upthrow side or downthrow side of the fault? The arrow points down, it must be the downthrow side. F ootwall D ownthrow T his does not make FUN! This is a reverse fault.

1 km Hanging wall Footwall ↿ ⇂ Reverse faults are caused by a pushing together motion (compression).

1 km ↿ ⇂ There are many more faults on this seismic profile. Click to see a few suggestions. Do you agree? ⇃ ↾ ⇃ ↾ ↿ ⇂ ↿ ⇂ ↿ ⇂ ↿ ⇂ ↿ ⇂

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