Fault (geology)

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 movement. Large faults within the Earth's crust result from the action of plate tectonic forces, with the largest forming the boundaries between the plates, such as subduction zones or transform faults. Energy release associated with rapid movement on active faults is the cause of most earthquakes. A fault plane is the plane. A fault trace or fault line is a place where the fault can be mapped on the surface. A fault trace is the line plotted on geologic maps to represent a fault. Since faults do not consist of a single, clean fracture, geologists use the term fault zone when referring to the zone of complex deformation associated with the fault plane. Owing to friction and the rigidity of the constituent rocks, the two sides of a fault cannot always glide or flow past each other and so all movement stops; the regions of higher friction along a fault plane, where it becomes locked, are called asperities.

Stress builds up when a fault is locked, when it reaches a level that exceeds the strength threshold, the fault ruptures and the accumulated strain energy is released in part as seismic waves, forming an earthquake. Strain occurs instantaneously, depending on the liquid state of the rock. A fault in ductile rocks can release instantaneously when the strain rate is too great. Slip is defined as the relative movement of geological features present on either side of a fault plane. A fault's sense of slip is defined as the relative motion of the rock on each side of the fault with respect to the other side. In measuring the horizontal or vertical separation, the throw of the fault is the vertical component of the separation and the heave of the fault is the horizontal component, as in "Throw up and heave out"; the vector of slip can be qualitatively assessed by studying any drag folding of strata, which may be visible on either side of the fault. In practice, it is only possible to find the slip direction of faults, an approximation of the heave and throw vector.

The two sides of a non-vertical fault are known as footwall. The hanging wall occurs above the fault plane and the footwall occurs below it; 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 above him. Based on the direction of slip, faults can be categorized as: strike-slip, where the offset is predominantly horizontal, parallel to the fault trace. In a strike-slip fault, the fault surface is near vertical, the footwall moves laterally either left or right with little vertical motion. Strike-slip faults with left-lateral motion are known as sinistral faults, those with right-lateral motion as dextral faults; each is defined by the direction of movement of the ground as would be seen by an observer on the opposite side of the fault. A special class of strike-slip fault is the transform fault; this class is related to an offset in a spreading center, such as a mid-ocean ridge, or, less common, within continental lithosphere, such as the Dead Sea Transform in the Middle East or the Alpine Fault in New Zealand.

Transform faults are referred to as "conservative" plate boundaries, inasmuch as lithosphere is neither created nor destroyed. Dip-slip faults can reverse. In a normal fault, the hanging wall moves relative to the footwall. A downthrown block between two normal faults dipping towards each other is a graben. An upthrown block between two normal faults dipping away from each other is 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 indicate compressive shortening of the crust; the dip of a reverse fault is steep, greater than 45°. The terminology of "normal" and "reverse" comes from coal-mining in England, where normal faults are the most common. 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 form ramps and fault-bend folds. Flat segments of thrust fault planes are known as flats, inclined sections of the thrust are known as ramps.

Thrust faults move within formations by forming flats and climb up sections with ramps. Fault-bend folds are formed by movement of the hanging wall over a non-planar fault surface and are found associated with both extensional and thrust faults. Faults may be reactivated at a time with the movement in the opposite direction to the original movement. A normal fault may therefore become a reverse vice versa. Thrust faults form nappes and klippen in the large thrust belts. Subduction zones are a special class of thrusts that form the largest faults on Earth and give rise to the largest earthquakes. A fault which has a component of dip-slip and a component of strike-slip is termed an o

Historical examples of flanking maneuvers

In military tactics, a flanking maneuver, or flanking manoeuvre, is an attack on the sides of an opposing force. If a flanking maneuver succeeds, the opposing force would be surrounded from two or more directions, which reduces the maneuverability of the outflanked force and its ability to defend itself. Flanking maneuvers played an important role in nearly every major battle in history, have been used by famous military leaders like Hannibal, Julius Caesar, Khalid ibn al-Walid, Saladin, Nader Shah, William Tecumseh Sherman and Stonewall Jackson throughout history. Sun Tzu's The Art of War emphasizes the use of flanking, although it does not advocate surrounding the enemy force as this may induce it to fight with greater ferocity if it cannot escape. A flanking maneuver is not always effective, as the flanking force may itself be ambushed while maneuvering, or the main force is unable to pin the defenders in place, allowing them to turn and face the flanking attack. During the second Persian invasion of Greece, after great losses at the Battle of Thermopylae and the Battle of Artemisium, the Greeks once again brought the Persians to blows in the Battle of Salamis in the year 480 BC.

The Greek fleet numbered 378 triremes. However, in the narrow confines of the straits, the numerical superiority of the Persians became an active hindrance; the Persians became disorganized in the cramped straits, the Greeks were in a position to flank from the northwest. Retreating Persian ships were befouled by the approaching second and third lines who were advancing to the line of battle. In the aftermath of the battle, Xerxes retreated to Asia with the majority of his army. In his wake he left Mardonius, who would be decisively defeated by the Greek army the following year in the Battle of Plataea. In 371 BC, the armies of Sparta and Thebes gave battle near the city of Leuctra, despite the superior numbers and fearful reputation of the Spartan army, the unbalanced Theban attack, with the Sacred Band of Thebes on the extreme left and in echelon formation disorganized the Spartan lines and spread confusion in its army. Before the extreme Spartan right wing had entered the fray, the battle was lost for them.

It shattered the myth of Spartan invincibility. The Battle of Leuctra has become the archetypal example of a flanking attack since, it inspired the adoption of the echelon formation by the Macedonian armies of Philip II and Alexander the Great. In 216 BC Hannibal accomplished one of the most famous flanking maneuvers of all history at the Battle of Cannae. Using a double flanking maneuver known as a Pincer movement, Hannibal managed to surround and kill nearly the entirety of a larger Consular Roman Army; the defeat sent the Roman Republic into complete disarray and remains a singular example of outstanding tactical leadership. As military historian Theodore Ayrault Dodge wrote: Few battles of ancient times are more marked by ability... than the battle of Cannae. The position was such as to place every advantage on Hannibal's side; the manner in which the far from perfect Hispanic and Gallic foot was advanced in a wedge in échelon... was first held there and withdrawn step by step, until it had the reached the converse position... is a simple masterpiece of battle tactics.

The advance at the proper moment of the African infantry, its wheel right and left upon the flanks of the disordered and crowded Roman legionaries, is far beyond praise. The whole battle, from the Carthaginian standpoint, is a consummate piece of art, having no superior, few equal, examples in the history of war. In 48 BC at the Battle of Pharsalus, Julius Caesar faced the army of Pompey, which not only outnumbered his more than four to one, but was in more or less friendly territory. Conversely, Caesar's own army, due to his blocked crossing of the Adriatic Sea, had been cut in half as well as cut off from their supply lines; the rest of the army lay on the opposing shores of the Adriatic, unable to aid their comrades. Anticipating a turning of his flank, Caesar had hidden a line of reserves in this area; when Pompey turned Caesar's cavalry, rather than finding a route through which to attack his enemy in the rear, he encountered 2,000 legionnaires. These were armed with pila a missile weapon such as a javelin, but the legionnaires used their length as a stabbing anti-cavalry weapon instead.

Having turned back the flank of his enemy, Caesar now found his own open flank, which he used to route the army of Pompey. After his defeat, Pompey fled to Egypt, the battle marked the effective end of the Wars of the First Triumvirate. On 29 December 1503, the Spanish army of Gonzalo Fernández de Córdoba crossed the River Garigliano using an upriver pontoon bridge to defeat the French army; the outnumbered Spaniard and Italian troops left the main army in front of the same positions they had keep against the French army of the Marquis of Saluzzo. The bold maneuver of the Gran Capitán spread terror in the demoralized French army that began to retreat; the Spanish main body, led by Andrade and Mendoza, crossed the river in front of the retreating army and transformed the retreat into a rout. Despite Chevalier Bayard brave rearguard actions at Mola bridge, the French army was forced to seek refuge in Gaeta where the surrendered a few days later; this victory and the previous one at the battle of Cerignola formed the basis for the fearful reputation of the Spanish infantry, the Tercios Viejos that lasted for more than a century until the battle of Rocroi.

The Ulm Campaign of September to October 1805 saw Napoleon Bonaparte engage in a monthlong maneuver aimed at severing Austrian lines and capturing an entire Aust

Pahranagat Valley

The Pahranagat Valley is a Tonopah Basin landform in Lincoln County, Nevada. The more fertile part of Pahranagat Valley is a narrow ribbon of green like an oasis in the vast Nevada desert, it is 40 miles long running north and south and is watered by three large natural springs of water and many smaller ones as well. It has two near the north end of the valley and two towards the south end; the southern half of the valley including the two lakes is home to the Pahranagat Valley National Wildlife Refuge. Pahranagat Valley is bordered on the west by a range of mountains called the Mount Irish Range and the Pahranagat Range, it is bordered on the east by the Hiko Range. State Route 318 and U. S. Route 93 traverse the entire length of the valley; the more inhabited areas in Pahranagat Valley include Hiko, Ash Springs and Alamo, the town of Alamo being the largest and where all of the schools for the valley are located. The closest town to Pahranagat Valley is over 50 miles to the east at Nevada; the Crystal Springs area, used as a watering spot and campsite, was a principal stop-over on the Mormon Trail Alternate Route.

In the late 1850s, the area was a haven for outlaws who pastured hundreds of head of stolen cattle and horses on its meadows. Silver ore was discovered in 1865 on Mount Irish, Logan sprang into existence. A mill to process the ore was built in the ruins of which are still in existence. Since the late 19th century, Pahranagat Valley has been an agricultural community. Presently it is a bedroom community for many who work in Las Vegas though the commute is over 100 miles one way; the geology of the region includes the Alamo meteor impact which scattered layers of impact debris across the area near Alamo. The Pahranagat Valley is home of several endangered species like Fluminicola merriami, Bufo nelsoni and endemic subspecies of Gila robusta, Rhinichthys osculus, Crenichthys baileyi, Microtus montanus. Nevada State Historic Preservation Office History of Lincoln County