The normal fault is not necessarily normal in the sense that
it is common....because.... it is not the most common of faults.
However what is normal about them is that their movement tends
to follow the gravitational pull on the fault blocks involved.
The fault plane on the normal fault is generally very steep. In
a normal fault the two involved blocks are (by gravity) pulling
away from one another causing one of the fault blocks to slip
upward and the other downward with respect to the fault plane
(it is hard to determine whether both or just one block has moved.).
The exposed upward block forms a cliff-like feature known as a
fault scarp. A scarp may range from a few to hundreds of meters
in height and their length may continue for 300 or more kilometers
(around 200 miles).
The phrase "initial stage"
means the beginning stages of a landform. Click here for a look
at a graben and horst system.
Probably the most well known and well studied fault is the
transcurrent (strike-slip) fault known as the San Andreas fault
of California. This fault marks the margin line between the Pacific
and North American Plates. Movement on a strike strip fault is
generally horizontal. On the surface, scarps form as hills crossing
the fault zone are torn apart by movement over time. Actually
anything crossing this fault zone is either slowly torn apart,
or offset. Rivers crossing the fault line are called offset streams
and are classic signatures of fault activity along the San Andreas.
These faults can be very long, the San Andreas is nearly 600 miles
In the 1994 Northridge, California event, a deep thrust fault
located about 18 km under the city of Los Angeles produced an
eartquake that registered a magnitude of 6.7. When thrust faults
are exposed on the surface overburnden material lies over the
main block. They are normally associated with areas of folded
surfaces and or mountaineous regions. The dip angles of thrust
faults are normally not as steep as a normal fault. Chief Mountain,
in Montana (one of the places we look at using the USGS quads
in the principles of geography class) is an example of a thrust
e-mail the teacher click
Just For Fun: The "grapevine hill" which disects
the San Andreas Fault on Interstate 5 in Southern California is
mentioned in what popular song? Better yet...who did the original
version......here's a hint:
"My daddy said, son your're gonna drive me to drinkin' if
you don't stop driving that .................."