normal or reverse? looking at the two types of vertical displacement in dip-slip faults using the...

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 walland

Footwall

The footwall is always underneath the fault

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

faul

t

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

This 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

Footwall

This is a normal fault.

Upthrow

Normal

⇃↾

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.

Footwall

Downthrow

This 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.

Footwall

Downthrow

This 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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