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Fault mechanics is a field of study that investigates the behavior of 
Intraplate earthquakes do not have a following force, and are not associated with mountain building. Thus, there is the puzzling question of how long any interior active zone has to live. For, in a solid stressed plate, every seismic displacement acts to relieve (reduce) stress; the fault zone should come to equilibrium; and all seismic activity cease. One can see this type of arching "lockup" in many natural processes.
In fact, the seismic zone (such as the New Madrid Fault Zone) is ensured eternal life by the action of water. As shown, if we add the equivalent of a giant funnel to the crack, it becomes the beneficiary of stress corrosion (the progressive weakening of the crack edge by water). If there is a continuing supply of new water, the system does not come to equilibrium, but continues to grow, ever relieving stress from a larger and larger volume.
Thus the prerequisite for a continuing seismically active interior zone is the presence of water, the ability of the water to get down to the fault source (high permeability), and the usual high horizontal interior stresses of the rock mass. All small earthquake zones have the potential to grow to resemble New Madrid or Charlevoix.
James N. Brune, Tectonic stress and the spectra of seismic shear waves from earthquakes, J. Geophys. Res. 75:4997-5009, 1970., review written in 1987. retrieved August 1, 2005
# [https://web.archive.org/web/20050308030140/http://www.seismo.nrcan.gc.ca/historic_eq/charpage_e.php Maurice Lamontagne, last modified 2003-12-22, The Charlevoix-Kamouraska* Seismic Zone, Canada - Natural Resources, Retrieved August 1, 2005] {{Structural geology Fields of seismology Structural geology
geologic fault
In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...
s.
Behind every good earthquake
An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, fr ...
is some weak rock. Whether the rock remains weak becomes an important point in determining the potential for bigger earthquakes.
On a small scale, fractured rock behaves essentially the same throughout the world, in that the angle of friction is more or less uniform (see Fault friction). A small element of rock in a larger mass responds to stress
Stress may refer to:
Science and medicine
* Stress (biology), an organism's response to a stressor such as an environmental condition
* Stress (linguistics), relative emphasis or prominence given to a syllable in a word, or to a word in a phrase ...
changes in a well defined manner: if it is squeezed by differential stresses greater than its strength, it is capable of large deformations. A band of weak, fractured rock in a competent mass can deform to resemble a classic geologic fault
In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...
. Using seismometer
A seismometer is an instrument that responds to ground noises and shaking such as caused by earthquakes, volcanic eruptions, and explosions. They are usually combined with a timing device and a recording device to form a seismograph. The outpu ...
s and earthquake location
The primary purpose of a seismometer is to locate the initiating points of earthquake epicenters. The secondary purpose, of determining the 'size' or Moment magnitude scale must be calculated after the precise location is known.
The earliest seis ...
, the requisite pattern of micro-earthquakes can be observed.
For earthquakes, it all starts with an embedded penny
A penny is a coin ( pennies) or a unit of currency (pl. pence) in various countries. Borrowed from the Carolingian denarius (hence its former abbreviation d.), it is usually the smallest denomination within a currency system. Presently, it is t ...
-shaped crack as first envisioned by Brune. As illustrated, an earthquake zone may start as a single crack, growing to form many individual cracks and collections of cracks along a fault. The key to fault growth is the concept of a "following force", as conveniently provided for interplate earthquake
An interplate earthquake is an earthquake that occurs at the boundary between two tectonic plates. Earthquakes of this type account for more than 90 percent of the total seismic energy released around the world. If one plate is trying to move pa ...
s, by the motion of tectonic plates. Under a following force, the seismic displacements eventually form a topographic feature, such as a mountain range.
Intraplate earthquakes do not have a following force, and are not associated with mountain building. Thus, there is the puzzling question of how long any interior active zone has to live. For, in a solid stressed plate, every seismic displacement acts to relieve (reduce) stress; the fault zone should come to equilibrium; and all seismic activity cease. One can see this type of arching "lockup" in many natural processes.
In fact, the seismic zone (such as the New Madrid Fault Zone) is ensured eternal life by the action of water. As shown, if we add the equivalent of a giant funnel to the crack, it becomes the beneficiary of stress corrosion (the progressive weakening of the crack edge by water). If there is a continuing supply of new water, the system does not come to equilibrium, but continues to grow, ever relieving stress from a larger and larger volume.
Thus the prerequisite for a continuing seismically active interior zone is the presence of water, the ability of the water to get down to the fault source (high permeability), and the usual high horizontal interior stresses of the rock mass. All small earthquake zones have the potential to grow to resemble New Madrid or Charlevoix.
See also
* * *Aseismic creep
In geology, aseismic creep or fault creep is measurable surface displacement along a fault in the absence of notable earthquakes. Aseismic creep may also occur as "after-slip" days to years after an earthquake. Notable examples of aseismic slip in ...
References
External links
James N. Brune, Tectonic stress and the spectra of seismic shear waves from earthquakes, J. Geophys. Res. 75:4997-5009, 1970., review written in 1987. retrieved August 1, 2005
# [https://web.archive.org/web/20050308030140/http://www.seismo.nrcan.gc.ca/historic_eq/charpage_e.php Maurice Lamontagne, last modified 2003-12-22, The Charlevoix-Kamouraska* Seismic Zone, Canada - Natural Resources, Retrieved August 1, 2005] {{Structural geology Fields of seismology Structural geology