Pine Mountain Overthrust Fault EarthCache
This cache has been locked, but it is available for viewing.
Pine Mountain Overthrust Fault
-
Difficulty:
-
-
Terrain:
-
Size: 
(not chosen)
Please note Use of geocaching.com services is subject to the terms and conditions
in our disclaimer.
Fine example of a fault line.
Here you are looking at the effects of Pine Mountain Overthrust
Fault Line. The Pine Mountain Overthrust Fault Line is 125-mile
overthrust fault created by mountain building forces that occurred
here roughly 230 million years ago. The sandstone and limestone
bedrock that forms this unique feature dip 30-45 degrees from the
crest to the southeast.
In geology, a fault or fault line is a planar rock fracture, which
shows evidence of relative movement. Large faults within the
Earth's crust are the result of shear motion and active fault zones
are the causal locations of most earthquakes. Earthquakes are
caused by energy release during rapid slippage along faults. The
largest examples are at tectonic plate boundaries but many faults
occur far from active plate boundaries. Since faults do not usually
consist of a single, clean fracture, the term fault zone is used
when referring to the zone of complex deformation that is
associated with the fault plane. The two sides of a non-vertical
fault are called the hanging wall and footwall. By definition, the
hanging wall occurs above the fault and the footwall occurs below
the fault. This terminology comes from mining. When working a
tabular ore body the miner stood with the footwall under his feet
and with the hanging wall hanging above him.
The creation and behaviour of faults, in both an individual small
fault and within the greater fault zones which define the tectonic
plates, is controlled by the relative motion of rocks on either
side of the fault surface.
Because of friction and the rigidity of the rock, the rocks cannot
simply glide or flow past each other. Rather, stress builds up in
rocks and when it reaches a level that exceeds the strain
threshold, the accumulated potential energy is released as strain,
which is focused into a plane along which relative motion is
accommodated — the fault.
Strain is both accumulative and instantaneous depending on the
rheology of the rock; the ductile lower crust and mantle
accumulates deformation gradually via shearing whereas the brittle
upper crust reacts by fracture, or instantaneous stress release to
cause motion along the fault. A fault in ductile rocks can also
release instantaneously when the strain rate is too great. The
energy released by instantaneous strain release is the cause of
earthquakes, a common phenomenon along transform boundaries.
Faults can be categorized into three groups based on the sense of
slip. A fault where the main sense of movement (or slip) on the
fault plane is vertical is known as a dip-slip fault. Where the
main sense of slip is horizontal the fault is known as a
transcurrent or strike-slip fault. Oblique-slip faults have
significant components of both strike and dip slip.
For all naming distinctions, it is the orientation of the net dip
and sense of slip of the fault which must be considered, not the
present-day orientation, which may have been altered by local or
regional folding or tilting.
Dip-slip faults include both normal and reverse. A normal fault
occurs when the crust is extended. Alternatively such a fault can
be called an extensional fault. The hanging wall moves downward,
relative to the footwall. A downthrown block between two normal
faults dipping towards each other is called a graben. An upthrown
block between two normal faults dipping away from each other is
called a horst. Low-angle normal faults with regional tectonic
significance may be designated detachment faults.
A reverse fault is the opposite of a normal fault — the hanging
wall moves up relative to the footwall. Reverse faults are
indicative of shortening of the crust. The dip of a reverse fault
is relatively steep, greater than 45°.
A thrust fault has the same sense of motion as a reverse fault, but
with the dip of the fault plane at less than 45°. Thrust faults
typically form ramps, flats and fault-bend (hanging wall and foot
wall) folds. Thrust faults are responsible for forming nappes and
klippen in the large thrust belts.
The fault plane is the plane that represents the fracture surface
of a fault. Flat segments of thrust fault planes are known as
flats, and inclined sections of the thrust are known as ramps.
Typically thrust faults move within formations by forming flats,
and climb up section with ramps.
Fault-bend folds are formed by movement of the hangingwall over a
non-planar fault surface and are found associated with both
extensional and thrust faults.
Faults may be reactivated at a later time with the movement in the
opposite direction to the original movement (fault inversion). A
normal fault may therefore become a reverse fault and vice versa.
The fault surface is usually near vertical and the footwall moves
either left or right or laterally with very little vertical motion.
Strike-slip faults with left-lateral motion are also known as
sinistral faults. Those with right-lateral motion are also known as
dextral faults. A special class of strike-slip faults is the
transform faults which are a plate tectonics feature related to
spreading centers such as mid-ocean ridges.
A fault which has a component of dip-slip and a component of
strike-slip is termed an 'oblique-slip fault'. Nearly all faults
will have some component of both dip-slip and strike-slip, so
defining a fault as oblique requires both dip and strike components
to be measurable and significant. Some oblique faults occur within
transtensional and transpressional regimes, others occur where the
direction of extension or shortening changes during the deformation
but the earlier formed faults remain active.
To get credit for this EC, post a photo of you with GPS and the
Fault in the back ground. Please answer the following questions.
1. What type of fault do you think this is?
2. Estimate how high the exposed fault is from the posted
coordinates.
3. What popular public place is near the EC?
Logs with no photo of the actual cacher logging the find or failure
to answer questions will result in a log deletion. Exceptions will
be considered if you contact me first (I realize sometimes we
forget our cameras or the batteries die). Logs that not not meet
logging requirements will be deleted without notice.
I have used sources available to me by using google search to get
information for this earth cache. I am by no means a geologist. I
use books, internet, and asking questions about geology just like
99.9 percent of the geocachers who create these great Earth Caches.
I enjoy Earth Caches and want people to get out and see what I see
everytime I go and explore this great place we live in.
Additional Hints
(No hints available.)
Treasures
You'll collect a digital Treasure from one of these collections when you find and log this geocache:
Loading Treasures