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 hanging wall is always on top of the fault
Hanging
wall
Footwall
The footwall is always underneath 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
1 km
We apply this to the fault we
looked at in the introduction to
faults.
Hanging
wall
Hanging Wall
Footwall
The block above the fault plane
is the hanging wall, and the
block below the fault is the
footwall.
Footwall
Draw arrows to show the
relative movement on either
side of the fault.
Hanging
wall
Footwall
Hanging
wall
Is the footwall the upthrow side
or downthrow side of the fault?
Upthrow
The arrow points up, it must be
the upthrow side.
Footwall
Upthrow
Normal
Footwall
This makes FU N !
This is a normal fault.
Hanging
wall
Normal faults are caused by a
pulling apart motion (tension).
Upthrow
Footwall
Another example
1 km
Hanging
wall
Two interpreted
horizons.
Two faults.
Look at the fault in
the NW.
The block above the
fault plane is the
hanging wall, and
the block below the
fault is the footwall.
Footwall
1 km
Hanging
wall
Footwall
Draw arrows to
show the relative
movement on either
side of the fault.
1 km
Hanging
wall
Is the footwall the
upthrow side or
downthrow side of
the fault?
The arrow points
down, it must be the
downthrow side.
Footwall
Downthrow
Footwall
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.
Hanging
wall
Footwall
The block above the
fault plane is the
hanging wall, and
the block below the
fault is the footwall.
1 km
Draw arrows to
show the relative
movement on either
side of the fault.
Hanging
wall
Footwall
1 km
Is the footwall the
upthrow side or
downthrow side of
the fault?
Hanging
wall
Footwall
The arrow points
down, it must be the
downthrow side.
Footwall
Downthrow
This does not
make FUN!
This is a reverse
fault.
1 km
Reverse faults are
caused by a pushing
together motion
(compression).
Hanging
wall
Footwall
1 km
There are many
more faults on this
seismic profile.
Click to see a few
suggestions.
Do you agree?