HISTORIAN'S PREDICTION: The 19th century historian Ivan Zabelin was right when he wrote: “Such world-historical cities as Moscow are born in their place not at the whim of some kind and wise prince Yuri Vladimirovich, not at the whim of a happy capricious chance, but by force causes and circumstances of a higher or deeper order.”

ANOMAL KOLOMENSKOYE: The first settlers of the places where the city now stands chose Kolomenskoye. This area, although considered one of anomalous zones capital, can have a beneficial effect on people. “Our ancestors settled not on the faults themselves, but in close proximity to them,” says Olga Tkachenko, senior researcher at the Russian Physical Society. - Radon gas is released from tectonic faults and cracks. This radioactive element is harmful in large doses, but, like many poisons, it is beneficial in small doses. It is even capable of strengthening the human skeleton, which is built in accordance with the parameters of the golden ratio.

THE FORTRESS WILL STAND: But the Kremlin stands not at the intersection of faults, but next to them. The fault runs through Red and Manezhnaya squares, and the fortress itself was built in a safe place, on Borovitsky Hill. In pagan times, by the way, there was a temple there.

TEMPLES ON Faults: Moscow churches were also built on faults. Why is not entirely clear. Apparently, the architecture of the temple is capable of transforming telluric (earthly) radiation, turning it into some kind of positive energy.”

TWO ZONES: The entire territory of Moscow is divided into two large geological zones. The north looks like a dome (it is slightly higher), the south looks like a bowl. The north is considered a more favorable territory for living, although if another earthquake occurs in the Southern Carpathians, these areas of the city will first feel its consequences. The fact is that the northern part of Moscow lies in the zone of global tectonic fault.

IN scientific literature, in publications on the Internet, in blogs and forums, the topic of tectonic faults is increasingly being raised and discussed. True, in the records they most often appear under the name of geopathogenic zones, apparently because this phrase is more often heard and has a pronounced mystical connotation. Meanwhile, most readers know almost nothing about such a phenomenon as a tectonic fault, because its roots lie not in mysticism and esotericism, but in a generally recognized, but not the most popular science today - geology.

A tectonic fault is a zone of disruption of the continuity of the earth's crust, a deformation seam that divides a rock mass into two blocks. Tectonic faults are present in any mountain range in any territory and have been studied by geologists for a long time. It is precisely tectonic faults that are most often associated with deposits of minerals - metal ores, hydrocarbons, groundwater, etc., which makes them a very useful object for research.

Until recently, in geology it was believed that the earth's crust, with the exception of areas of active volcanism and seismic phenomena (dangerous in terms of earthquakes), is in a state of rest, i.e. motionless. However, at the present stage, with the commissioning of new measuring equipment, it has become obvious that the earth's crust is constantly in motion. Roughly speaking, the earth moves right under our feet. These movements have insignificant amplitude and are not noticeable to the eye, however, they can have a significant impact, both on arrays rocks, and on engineering structures.

Why is the earth's crust mobile? In accordance with Newton's first law, movement occurs under the influence of force. Forces are constantly acting in the earth's crust (one of them is gravity), as a result of which the geological environment is always in a stressed state. Since rocks are always overstressed, they begin to deform and collapse. Most often this is expressed in the formation of tectonic sutures (ruptures) or displacement of rock blocks along previously formed active faults.

Modern displacements along active faults can lead to deformation earth's surface and exert a mechanical effect on engineering facilities. There are known cases when, in zones of active faults, destruction of buildings and structures occurred, constant breaks in water-carrying communications, and the formation of cracks in walls and foundations. Similar emergency buildings and structures exist in almost every city. But cases of deformation of buildings, most often, are not given wide publicity.

The topic of the negative impact of tectonic faults (geopathogenic zones) on human health is often discussed. To date, there are a number of scientific studies on this topic. As a rule, the authors note that tectonic faults do have an impact on living organisms, and this impact may be ambiguous for various types plants and animals. Basically, among researchers there is an opinion that the impact of tectonic faults on humans is predominantly negative. Some people react quite sharply to tectonic zones, within which their well-being sharply deteriorates. Most people tolerate their stay in fault zones quite calmly, but some deterioration in their condition is noted. A small percentage of people are virtually unaffected by tectonic zones.

It is quite difficult to explain the principles of the negative impact of tectonic disturbance zones on human health. The processes occurring in zones of tectonic disturbances are complex and diverse. An active fault is a zone of concentration of tectonic stress and a zone of increased deformation of the rock mass. Many geologists and geomechanics believe that an overstressed fault zone generates an electromagnetic field. Just like, for example, a mechanical effect on a quartz crystal in a piezoelectric lighter generates a current discharge. In addition, due to increased fracturing, the tectonic fault, in most cases, is an aquifer zone. It is quite obvious that the movement of groundwater with salts dissolved in them (conductor) through the thickness of rocks (which differ in their electrical properties) can and does form electric fields and anomalies. That is why anomalies of various natural physical fields are often observed in tectonic fault zones. These anomalies are widely used to search and identify zones of tectonic disturbances in modern geophysics. Most likely, these anomalies also serve as the main source of impact on living organisms, incl. per person.

To date, the problem of studying the influence of tectonic faults on engineering objects and on human health is studied only on the initiative of independent researchers. There are no targeted official programs in this direction. The presence of active tectonic faults is not taken into account when selecting sites for the construction of residential buildings. The issues of searching and identifying zones of displacement of the earth's surface are dealt with only in very rare cases during the construction of objects of a high level of responsibility. In general, it is obvious that among geologists, designers and builders there is a need for a targeted study of anomalous tectonic zones and mandatory consideration of the geodynamic activity of the geological environment in the process of its development.

Geological fault, or gap— violation of the continuity of rocks, without displacement (crack) or with displacement of rocks along the surface of the rupture. The faults prove relative motion earth masses. Major faults in the earth's crust are the result of shear tectonic plates at their junctions. Active fault zones often experience earthquakes as a result of the release of energy during rapid sliding along a fault line. Since most often faults do not consist of a single crack or rupture, but of a structural zone of similar tectonic deformations that are associated with the fault plane, such zones are called fault zones.

The two sides of a non-vertical fault are called hanging side And sole(or recumbent side) - by definition, the first occurs above and the second below the fault line. This terminology comes from the mining industry.

Types of faults

Geological faults are divided into three main groups depending on the direction of movement. A fault in which the main direction of movement occurs in the vertical plane is called fault with dip displacement; if in the horizontal plane, then shift. If the displacement occurs in both planes, then such a displacement is called fault-shift. In any case, the name applies to the direction of movement of the fault, and not to the present orientation, which may have been changed by local or regional folds or tilts.

San Andreas Fault California, USA

A fracture in a metamorphic layer near Adelaide, Australia

Fault with dip offset

Faults with dip displacement are divided into discharges, reverse faults And thrusts. Faults occur when the earth's crust stretches, when one block of the earth's crust (the hanging wall) sinks relative to another (the footwall). A section of the earth's crust that is lowered relative to the surrounding fault areas and located between them is called graben. If the section, on the contrary, is raised, then such a section is called handful. Faults of regional significance with a small angle are called breakdown, or peeling. Reverse faults occur in the opposite direction - in them the hanging wall moves upward relative to the base, while the angle of inclination of the crack exceeds 45°. During reverse faults, the earth's crust contracts. Another type of fault with dip displacement is thrust, in it the movement occurs similar to a reverse fault, but the angle of inclination of the crack does not exceed 45°. Thrusts usually form slopes, rifts and folds. As a result, tectonic nappes and clips. A fault plane is the plane along which the rupture occurs.

Shifts

During shear, the fault surface is vertical and the base moves to the left or right. In left-sided shifts, the sole moves to the left side, in right-sided shifts - to the right. Separate view shift is transform fault, which runs perpendicular to the mid-ocean ridges and breaks them into segments averaging 400 km wide.

Fault rocks

All faults have a measurable thickness, which is calculated by the size of the deformed rocks, which determine the layer of the earth's crust where the rupture occurred, the type of rocks that underwent deformation and the presence of mineralization fluids in nature. A fault passing through different layers of the lithosphere will have Various types rocks on a fault line. Long-term displacement along the dip leads to the overlapping of rocks with characteristics different levels earth's crust. This is especially noticeable in cases of failures or large thrust faults.

The main types of rocks at faults are the following:

• Cataclasite is a rock whose texture is due to the structureless, fine-grained rock material.
• Mylonite is a shale metamorphic rock formed by the movement of rock masses along the surfaces of tectonic faults, by crushing, grinding and squeezing the minerals of the original rocks.
• Tectonic breccia is a rock consisting of acute-angled, unrounded rock fragments and cement connecting them. It is formed as a result of crushing and mechanical abrasion of rocks in fault zones.
• Fault mud is a loose, clay-rich soft rock, in addition to ultrafine-grained catalytic material, which may have a planar pattern and contain< 30 % видимых фрагментов.
• Pseudotachylyte is an ultrafine-grained, glassy rock, usually black in color.

Indication of deep faults

The location of deep faults can be determined on the Earth's surface using helium photography. Helium, as a product of the decay of radioactive elements saturating the upper layer of the earth's crust, seeps through cracks, rises into the atmosphere, and then into space. Such cracks, and especially the places where they intersect, have high concentrations of helium. This phenomenon was first established by the Russian geophysicist I. N. Yanitsky during searches uranium ores, recognized as scientific discovery and entered into State Register discoveries of the USSR under No. 68 with priority from 1968 in the following wording: “A previously unknown pattern has been experimentally established, namely that the distribution of anomalous (increased) concentrations of free mobile helium depends on deep, including ore-bearing, faults in the earth’s crust.”

Plate tectonics

Material from Wikipedia - the free encyclopedia

Map of lithospheric plates

Plate tectonics- modern geological theory about the movement of the lithosphere. She argues that the earth's crust consists of relatively integral blocks - plates that are located in constant movement each other relative to each other. Moreover, in expansion zones (mid-ocean ridges and continental rifts) as a result of spreading (eng. seafloor spreading- spreading of the seabed) a new one is formed oceanic crust, and the old one is absorbed in subduction zones. The theory explains earthquakes, volcanic activity and mountain building, much of which occurs at plate boundaries.

The idea of ​​the movement of crustal blocks was first proposed in the theory of continental drift, proposed by Alfred Wegener in the 1920s. This theory was initially rejected. The revival of the idea of ​​​​movements in the solid shell of the Earth (“mobilism”) occurred in the 1960s, when, as a result of studies of relief and geology, ocean floor Data were obtained indicating the processes of expansion (spreading) of the oceanic crust and the subduction of some parts of the crust under others (subduction). Combining these views with old theory continental drift gave rise to modern theory plate tectonics, which soon became a generally accepted concept in the earth sciences.

In the theory of plate tectonics, a key position is occupied by the concept of geodynamic setting - a characteristic geological structure with a certain ratio of plates. In the same geodynamic setting, the same type of tectonic, magmatic, seismic and geochemical processes occur.

History of the theory

For more information on this topic see: History of plate tectonics theory.

The basis of theoretical geology at the beginning of the 20th century was the contraction hypothesis. The earth cools like a baked apple, and wrinkles appear on it in the form of mountain ranges. These ideas were developed by the theory of geosynclines, created on the basis of the study of folded structures. This theory was formulated by James Dana, who added the principle of isostasy to the contraction hypothesis. According to this concept, the Earth consists of granites (continents) and basalts (oceans). When the Earth contracts, tangential forces arise in the ocean basins, which press on the continents. The latter rise in mountain ranges, and then are destroyed. The material that results from destruction is deposited in the depressions.

The German meteorologist Alfred Wegener opposed this scheme. On January 6, 1912, he spoke at a meeting of the German Geological Society with a report on continental drift. The starting point for the creation of the theory was the coincidence of the outlines of the western coast of Africa and the eastern coast of South America. If these continents are shifted, then they coincide, as if they were formed as a result of the split of one proto-continent.

Wegener was not satisfied with the coincidence of the outlines of the coasts (which had been repeatedly noticed before him), but began to intensively search for evidence of the theory. To do this, he studied the geology of the coasts of both continents and found many similar geological complexes, which coincided when combined, just like the coastline. Another direction to prove the theory was paleoclimatic reconstructions, paleontological and biogeographical arguments. Many animals and plants have limited ranges on both sides of the Atlantic Ocean. They are very similar, but separated by many kilometers of water, and it is difficult to imagine that they crossed the ocean.

In addition, Wegener began to look for geophysical and geodetic evidence. However, at that time the level of these sciences was clearly not sufficient to record the modern movement of the continents. In 1930, Wegener died during an expedition in Greenland, but before his death he already knew that the scientific community did not accept his theory.

Initially continental drift theory was received favorably by the scientific community, but in 1922 it was subjected to severe criticism from several well-known specialists. The main argument against the theory was the question of the force that moves the plates. Wegener believed that the continents moved along the basalts of the ocean floor, but this required enormous force, and no one could name the source of this force. The Coriolis force, tidal phenomena and some others were proposed as a source of plate movement, but the simplest calculations showed that all of them were absolutely insufficient to move huge continental blocks.

Critics of Wegener's theory focused on the question of the force moving the continents, and ignored all the many facts that certainly confirmed the theory. In fact, they found a single question in which new concept was powerless, and without constructive criticism rejected the main evidence. After the death of Alfred Wegener, the theory of continental drift was rejected, receiving the status of a marginal science, and the vast majority of research continued to be carried out within the framework of the theory of geosynclines. True, she also had to look for explanations of the history of the settlement of animals on the continents. For this purpose, land bridges were invented that connected the continents, but plunged into the depths of the sea. This was another birth of the legend of Atlantis. It is worth noting that some scientists did not recognize the verdict of world authorities and continued to search for evidence of continental movement. Tak du Toit ( Alexander du Toit) explained the formation of the Himalayan mountains by the collision of Hindustan and the Eurasian plate.

The sluggish struggle of the fixists, as supporters of the absence of significant horizontal movements were called, and the mobilists, who argued that the continents were still moving, with new strength erupted in the 1960s, when the study of the ocean floors revealed clues to the “machine” called the Earth.

By the early 1960s, a relief map of the ocean floor was compiled, which showed that mid-ocean ridges are located in the center of the oceans, which rise 1.5-2 km above the abyssal plains covered with sediment. These data allowed R. Dietz and Harry Hess to put forward the spreading hypothesis in 1962-1963. According to this hypothesis, convection occurs in the mantle at a speed of about 1 cm/year. The ascending branches of convection cells carry out mantle material under the mid-ocean ridges, which renews the ocean floor in the axial part of the ridge every 300-400 years. Continents do not float on the oceanic crust, but move along the mantle, being passively “soldered” into lithospheric plates. According to the concept of spreading, ocean basins have a variable and unstable structure, while continents are stable.

Age of the ocean floor (red color corresponds to young crust)

In 1963, the spreading hypothesis received strong support in connection with the discovery of striped magnetic anomalies on the ocean floor. They were interpreted as a record of reversals of the Earth's magnetic field, recorded in the magnetization of basalts of the ocean floor. After this, plate tectonics began its triumphant march in the earth sciences. More and more scientists realized that, rather than waste time defending the concept of fixism, it was better to look at the planet from the point of view new theory and, finally, begin to provide real explanations for the most complex earthly processes.

Plate tectonics has now been confirmed by direct measurements of plate velocity using the interferometry radiation from distant quasars and measurements using GPS satellite navigation systems. The results of many years of research have fully confirmed the basic principles of the theory of plate tectonics.

Current state of plate tectonics

Over the past decades, plate tectonics has significantly changed its basic principles. Nowadays they can be formulated as follows:

• The upper part of the solid Earth is divided into a brittle lithosphere and a plastic asthenosphere. Convection in the asthenosphere - main reason plate movements.

• The modern lithosphere is divided into 8 large plates, dozens of medium plates and many small ones. Small slabs are located in the belts between large slabs. Seismic, tectonic, and magmatic activity is concentrated at plate boundaries.

• Lithospheric plates, to a first approximation, are described as solids, and their motion obeys Euler's rotation theorem.

• There are three main types of relative plate movements

1. divergence (divergence), expressed by rifting and spreading;
2. convergence (convergence) expressed by subduction and collision;
3. shear movements along transform geological faults.

• Spreading in the oceans is compensated by subduction and collision along their periphery, and the radius and volume of the Earth are constant up to the thermal compression of the planet (in any case, the average temperature of the Earth's interior slowly decreases over billions of years).

• The movement of lithospheric plates is caused by their entrainment by convective currents in the asthenosphere.

There are two fundamentally different types the earth's crust - continental crust (more ancient) and oceanic crust (not older than 200 million years). Some lithospheric plates are composed exclusively of oceanic crust (an example is the largest Pacific plate), others consist of a block of continental crust welded into the oceanic crust.

More than 90% of the Earth's surface in the modern era is covered by 8 largest lithospheric plates:

• Australian plate
• Antarctic plate
• African plate
• Eurasian plate
• Hindustan plate
• Pacific Plate
• North American Plate
• South American Plate

Medium-sized plates include the Arabian Peninsula, as well as the Cocos and Juan de Fuca plates, remnants of the enormous Faralon plate that formed much of the Pacific Ocean floor but has now disappeared in the subduction zone beneath the Americas.

The force that moves the plates

Now there is no longer any doubt that the horizontal movement of plates occurs due to mantle thermogravitational currents - convection. The source of energy for these currents is the difference in temperature between the central regions of the Earth, which have a very high temperature (estimated core temperature is about 5000 °C) and the temperature on its surface. Heated in central zones The rock lands are expanding (see. thermal expansion), their density decreases, and they float up, giving way to descending colder and therefore heavier masses, which have already given up some of the heat to the earth’s crust. This process of heat transfer (a consequence of the floating of light-hot masses and the sinking of heavy-colder masses) occurs continuously, resulting in convective flows. These flows - currents close on themselves and form stable convective cells, consistent in the directions of flows with neighboring cells. At the same time, in the upper part of the cell, the flow of matter occurs almost in a horizontal plane, and it is this part of the flow that drags the plates in the horizontal direction with enormous force due to the enormous viscosity of the mantle matter. If the mantle were completely liquid - the viscosity of the plastic mantle under the crust would be low (say, like water or something like that), then transverse seismic waves could not pass through a layer of such a substance with low viscosity. And the earth's crust would be carried away by the flow of such matter with a relatively small force. But, due to the high pressure, at relatively low temperatures prevailing on the surface of Mohorovicic and below, the viscosity of the mantle substance here is very high (so on the scale of years, the substance of the Earth’s mantle is liquid (fluid), and on the scale of seconds it is solid).

The driving force for the flow of viscous mantle matter directly below the crust is the difference in heights of the free surface of the mantle between the region of rise and the region of descent of the convection flow. This height difference, one might say, the magnitude of the deviation from isostasy, is formed due to the different densities of the slightly hotter (in the ascending part) and slightly colder substance, since the weight of the hotter and colder columns in equilibrium is the same (at different densities!). In fact, the position of the free surface cannot be measured, it can only be calculated (the height of the Mohorovicic surface + the height of the column of mantle material, equivalent in weight to the layer of lighter crust above the Mohorovicic surface).

This same driving force(height difference) determines the degree of elastic horizontal compression of the crust by the force of viscous friction of the flow against the earth's crust. The magnitude of this compression is small in the region of the ascent of the mantle flow and increases as it approaches the place of descent of the flow (due to the transmission of compressive stress through the stationary hard bark in the direction from the place of ascent to the place of descent of the flow). Above the descending flow, the compression force in the crust is so great that from time to time the strength of the crust is exceeded (in the region of lowest strength and highest stress), and inelastic (plastic, brittle) deformation of the crust occurs—an earthquake. At the same time, entire mountain ranges, for example, the Himalayas, are squeezed out from the place where the crust is deformed (in several stages).

During plastic (brittle) deformation, the stress in it—the compressive force at the source of the earthquake and its surroundings—reduces very quickly (at the rate of crustal displacement during an earthquake). But immediately after the end of the inelastic deformation, the very slow increase in stress (elastic deformation), interrupted by the earthquake, continues due to the very slow movement of the viscous mantle flow, beginning the cycle of preparation for the next earthquake.

Thus, the movement of plates is a consequence of the transfer of heat from the central zones of the Earth by very viscous magma. In this case, part of the thermal energy is converted into mechanical work to overcome frictional forces, and part, having passed through the earth’s crust, is radiated into the surrounding space. So our planet is, in a sense, a heat engine.

Regarding the reason high temperature There are several hypotheses about the interior of the Earth. At the beginning of the 20th century, the hypothesis of the radioactive nature of this energy was popular. It seemed to be confirmed by estimates of the composition of the upper crust, which showed very significant concentrations of uranium, potassium and other radioactive elements, but subsequently it turned out that the content of radioactive elements in the rocks of the earth’s crust is completely insufficient to ensure the observed flow of deep heat. And the content of radioactive elements in the subcrustal material (close in composition to the basalts of the ocean floor) can be said to be negligible. However, this does not exclude a fairly high content of heavy radioactive elements that generate heat in the central zones of the planet.

Another model explains the heating by chemical differentiation of the Earth. The planet was originally a mixture of silicate and metallic substances. But simultaneously with the formation of the planet, its differentiation into separate shells began. The denser metal part rushed to the center of the planet, and silicates concentrated in the upper shells. Wherein potential energy system decreased and turned into thermal energy.

Other researchers believe that the heating of the planet occurred as a result of accretion during meteorite impacts on the surface of the nascent celestial body. This explanation is doubtful - during accretion, heat was released almost on the surface, from where it easily escaped into space, and not into the central regions of the Earth.

Secondary forces

The force of viscous friction arising as a result of thermal convection plays a decisive role in the movements of plates, but in addition to it, other, smaller, but also important forces act on the plates. These are Archimedes' forces, ensuring the floating of a lighter crust on the surface of a heavier mantle. Tidal forces caused by the gravitational influence of the Moon and the Sun (the difference in their gravitational influence on points of the Earth at different distances from them). As well as the forces arising from changes atmospheric pressure on different parts of the earth's surface - atmospheric pressure forces often change by 3%, which is equivalent to a continuous layer of water 0.3 m thick (or granite at least 10 cm thick). Moreover, this change can occur in a zone hundreds of kilometers wide, while the change in tidal forces occurs more smoothly - over distances of thousands of kilometers.

Divergent boundaries or plate boundaries

These are the boundaries between plates moving in opposite sides. In the Earth's topography, these boundaries are expressed as rifts, where tensile deformations predominate, the thickness of the crust is reduced, the heat flow is maximum, and active volcanism occurs. If such a boundary forms on a continent, then a continental rift is formed, which can later turn into an oceanic basin with an oceanic rift in the center. In oceanic rifts, new oceanic crust is formed as a result of spreading.

Ocean rifts

Scheme of the structure of the mid-ocean ridge

For more on this topic, see: Mid-Ocean Ridge.

On the oceanic crust, rifts are confined to central parts mid-ocean ridges. New oceanic crust is formed in them. Their total length is more than 60 thousand kilometers. They are home to many hydrothermal springs, which carry a significant portion of deep heat and dissolved elements into the ocean. High temperature sources are called black smokers, significant reserves are associated with them non-ferrous metals.

Continental rifts

The splitting of the continent into parts begins with the formation of a rift. The crust thins and moves apart, and magmatism begins. An extended linear depression with a depth of about hundreds of meters is formed, which is limited by a series of faults. After this, two scenarios are possible: either the expansion of the rift stops and it fills sedimentary rocks, turning into an aulacogen, or the continents continue to move apart and between them, already in typically oceanic rifts, oceanic crust begins to form.

Convergent boundaries

For more on this topic, see: Subduction Zone.

Convergent boundaries are boundaries where plates collide. Three options are possible:

1. Continental plate with oceanic plate. Oceanic crust is denser than continental crust and sinks beneath the continent in a subduction zone.
2. Oceanic plate with oceanic plate. In this case, one of the plates creeps under the other and a subduction zone is also formed, above which an island arc is formed.
3. Continental plate with continental one. A collision occurs and a powerful folded area appears. A classic example is the Himalayas.

In rare cases, oceanic crust is pushed onto the continental crust - obduction. Thanks to this process, ophiolites of Cyprus, New Caledonia, Oman and others arose.

Subduction zones absorb oceanic crust, thereby compensating for its appearance at mid-ocean ridges. They occur exclusively complex processes, interactions between the crust and the mantle. Thus, the oceanic crust can pull blocks of continental crust into the mantle, which, due to low density, are exhumed back into the crust. This is how metamorphic complexes of ultra-high pressures arise, one of the most popular objects of modern geological research.

Majority modern zones subductions are located along the periphery of the Pacific Ocean, forming the Pacific fire ring. The processes occurring in the plate convection zone are rightfully considered to be among the most complex in geology. It mixes blocks of different origins, forming a new continental crust.

Active continental margins

Active continental margin

For more on this topic, see: Active Continental Margin.

An active continental margin occurs where oceanic crust subducts beneath a continent. The standard of this geodynamic situation is considered to be the western coast of South America; it is often called Andean type of continental margin. The active continental margin is characterized by numerous volcanoes and generally powerful magmatism. Melts have three components: the oceanic crust, the mantle above it, and the lower continental crust.

Beneath the active continental margin, there is active mechanical interaction between the oceanic and continental plates. Depending on the speed, age and thickness of the oceanic crust, several equilibrium scenarios are possible. If the plate moves slowly and has a relatively low thickness, then the continent scrapes off the sedimentary cover from it. Sedimentary rocks are crushed into intense folds, metamorphosed and become part of the continental crust. The resulting structure is called accretionary wedge. If the speed of the subducting plate is high and the sedimentary cover is thin, then the oceanic crust erases the bottom of the continent and draws it into the mantle.

Island arcs

Island arc For more information on this topic, see: Island arc.

Island arcs are chains of volcanic islands above a subduction zone, occurring where an oceanic plate subducts beneath an oceanic plate. Typical modern island arcs include the Aleutian, Kuril, Mariana Islands, and many other archipelagos. Japanese islands also often called an island arc, but their foundation is very ancient and in fact they were formed by several complexes of island arcs at different times, so the Japanese islands are a microcontinent.

Island arcs are formed when two oceanic plates collide. In this case, one of the plates ends up at the bottom and is absorbed into the mantle. Island arc volcanoes form on the upper plate. The curved side of the island arc is directed towards the absorbed plate. On this side there is a deep-sea trench and a forearc trough.

Behind the island arc there is a back-arc basin ( typical examples: Sea of ​​Okhotsk, South China Sea, etc.) in which spreading can also occur.

Continental collision

Collision of continents

For more information on this topic, see: Continental collision.

The collision of continental plates leads to the collapse of the crust and the formation of mountain ranges. An example of a collision is Alpine-Himalayan mountain belt, formed as a result of the closure of the Tethys Ocean and the collision with the Eurasian plate of Hindustan and Africa. As a result, the thickness of the crust increases significantly; under the Himalayas it reaches 70 km. This is an unstable structure; it is intensively destroyed by surface and tectonic erosion. In the crust with a sharply increased thickness, granites are smelted from metamorphosed sedimentary and igneous rocks. This is how the largest batholiths were formed, for example, Angara-Vitimsky and Zerendinsky.

Transform boundaries

Where plates move in parallel courses, but at different speeds, transform faults arise - enormous shear faults, widespread in the oceans and rare on continents.

Transform faults

For more information on this topic, see: Transform fault.

In the oceans, transform faults run perpendicular to mid-ocean ridges (MORs) and break them into segments averaging 400 km wide. Between the ridge segments there is an active part of the transform fault. Earthquakes and mountain building constantly occur in this area; numerous feathering structures are formed around the fault - thrusts, folds and grabens. As a result, mantle rocks are often exposed in the fault zone.

On both sides of the MOR segments there are inactive parts of transform faults. There are no active movements in them, but they are clearly expressed in the topography of the ocean floor by linear uplifts with a central depression.

Transform faults form a regular network and, obviously, do not arise by chance, but due to objective physical reasons. Data set numerical modeling, thermophysical experiments and geophysical observations made it possible to find out that mantle convection has three-dimensional structure. In addition to the main flow from the MOR, longitudinal currents arise in the convective cell due to the cooling of the upper part of the flow. This cooled substance rushes down along the main direction of the mantle flow. Transform faults are located in the zones of this secondary descending flow. This model agrees well with the data on heat flow: a decrease in heat flow is observed above transform faults.

Continental shifts

For more information on this topic, see: Shift.

Strike-slip plate boundaries on continents are relatively rare. Perhaps the only currently active example of a boundary of this type is the San Andreas Fault, which separates the North American Plate from the Pacific Plate. The 800-mile San Andreas Fault is one of the most seismically active areas on the planet: plates move relative to each other by 0.6 cm per year, earthquakes with a magnitude of more than 6 units occur on average once every 22 years. The city of San Francisco and much of the San Francisco Bay area are built in close proximity to this fault.

Within-plate processes

The first formulations of plate tectonics argued that volcanism and seismic phenomena are concentrated along plate boundaries, but it soon became clear that specific tectonic and magmatic processes also occur within plates, which were also interpreted within the framework of this theory. Among intraplate processes special place occupied by the phenomena of long-term basaltic magmatism in some areas, the so-called hot spots.

Hot Spots

There are numerous volcanic islands at the bottom of the oceans. Some of them are located in chains with successively changing ages. Classic example The Hawaiian Underwater Ridge became such an underwater ridge. It rises above the surface of the ocean in the form of the Hawaiian Islands, from which a chain of seamounts with continuously increasing age extends to the northwest, some of which, for example, Midway Atoll, come to the surface. At a distance of about 3000 km from Hawaii, the chain turns slightly north and is called Imperial Ridge. He breaks off at deep sea trench in front of the Aleutian island arc.

To explain this amazing structure, it was suggested that under Hawaiian Islands there is a hot spot - a place where a hot mantle flow rises to the surface, which melts the oceanic crust moving above it. There are many such points now installed on Earth. The mantle flow that causes them was called a plume. In some cases, the origin of the plume matter is assumed to be extremely deep, down to the core-mantle boundary.

Traps and oceanic plateaus

In addition to long-term hot spots, enormous outpourings of melts sometimes occur inside the plates, which form traps on the continents and oceanic plateaus in the oceans. The peculiarity of this type of magmatism is that it occurs in a short geological sense of time- about several million years, but covers huge areas (tens of thousands of km²); at the same time, a colossal volume of basalts is poured out, comparable to their amount crystallizing in the mid-ocean ridges.

Siberian traps are known for East Siberian platform, traps of the Deccan plateau on the Hindustan continent and many others. Hot mantle flows are also considered to be the cause of the formation of traps, but unlike hot spots, they act for a short time, and the difference between them is not entirely clear.

From point of view kinematic approach, plate movements can be described geometric laws moving figures on the sphere. The earth is viewed as a mosaic of slabs different sizes, moving relative to each other and the planet itself. Paleomagnetic data allows us to reconstruct the position of the magnetic pole relative to each plate at different points in time. Generalization of data for different plates led to the reconstruction of the entire sequence of relative movements of the plates. Combining this data with information obtained from fixed hot spots made it possible to determine the absolute movements of the plates and the history of the movement of the Earth's magnetic poles.

Thermophysical approach considers the Earth as a heat engine in which thermal energy is partially converted into mechanical energy. Within the framework of this approach, the movement of matter in the inner layers of the Earth is modeled as a flow of a viscous fluid described by the Navier-Stokes equations. Mantle convection is accompanied by phase transitions and chemical reactions, which play a decisive role in the structure of mantle flows. Based on geophysical sounding data, the results of thermophysical experiments and analytical and numerical calculations, scientists are trying to detail the structure of mantle convection, find flow velocities and other important characteristics of deep processes. These data are especially important for understanding the structure of the deepest parts of the Earth - the lower mantle and core, which are inaccessible for direct study, but undoubtedly have a huge impact on the processes occurring on the surface of the planet.

Geochemical approach. For geochemistry, plate tectonics is important as a mechanism for the continuous exchange of matter and energy between the various layers of the Earth. Each geodynamic setting is characterized by specific rock associations. In turn, according to these characteristic features it is possible to determine the geodynamic setting in which the rock was formed.

Historical approach. In terms of the history of planet Earth, plate tectonics is the history of continents joining and breaking apart, the birth and decline of volcanic chains, and the appearance and closure of oceans and seas. Now for large blocks of the crust the history of movements has been established in great detail and over a significant period of time, but for small plates the methodological difficulties are much greater. The most complex geodynamic processes occur in plate collision zones, where mountain ranges are formed, composed of many small heterogeneous blocks - terranes. When studying the Rocky Mountains, a special direction of geological research arose - terrane analysis, which incorporated a set of methods for identifying terranes and reconstructing their history.

For more information on this topic, see: Ancient continents.

For more information on this topic see: History of plate movements.

Reconstructing past plate movements is one of the main subjects of geological research. With varying degrees of detail, the position of the continents and the blocks from which they were formed has been reconstructed up to the Archean.

From the analysis of continental movements it was concluded empirical observation that continents gather every 400-600 million years into a huge continent containing almost the entire continental crust - a supercontinent. Modern continents were formed 200-150 million years ago, as a result of the breakup of the supercontinent Pangea. Now the continents are at a stage of almost maximum separation. Atlantic Ocean expands and the Pacific Ocean closes. Hindustan is moving north and crushing the Eurasian plate, but, apparently, the resource of this movement is almost exhausted, and in the near geological time a new subduction zone will arise in the Indian Ocean, in which the oceanic crust Indian Ocean will be absorbed under the Indian continent.

The influence of plate movements on climate

Location of large land masses in circumpolar regions contributes to a general decrease in the temperature of the planet, since glaciations can form on the continents. The more widespread glaciation is, the greater the planet's albedo and the lower the average annual temperature.

In addition, the relative position of the continents determines oceanic and atmospheric circulation.

However, a simple and logical scheme: continents in the polar regions - glaciation, continents in the equatorial regions - increase in temperature, turns out to be incorrect when compared with geological data about the Earth's past. Quaternary glaciation really happened when in the area South Pole turned out to be Antarctica, and in the northern hemisphere Eurasia and North America approached North Pole. On the other hand, the strongest Proterozoic glaciation, during which the Earth was almost completely covered with ice, occurred when most of the continental masses were in the equatorial region.

In addition, significant changes in the position of the continents occur over a period of about tens of millions of years, while the total duration of ice ages is of the order of several million years, and during one ice age Cyclic changes of glaciations and interglacial periods occur. All these climate changes occur quickly compared to the speed of continental movement, and therefore plate movement cannot be the cause.

From the above it follows that plate movements do not play a decisive role in climate change, but can be an important additional factor “pushing” them.

The meaning of plate tectonics

Plate tectonics has played a role in earth sciences comparable to heliocentric a concept in astronomy, or the discovery of DNA in genetics. Before the adoption of the theory of plate tectonics, earth sciences were descriptive in nature. They achieved a high level of perfection in describing natural objects, but rarely could explain the causes of processes. Opposite concepts could dominate in different branches of geology. Plate tectonics connected the various earth sciences and gave them predictive power.

The record-breaking earthquake and subsequent tsunami that hit Japan early Friday is a stark reminder of the devastating natural disasters that can strike populated cities - especially those in high-risk areas such as along major fault lines. earth's crust.
Take a look at the five cities most at risk similar disasters because of its location.
Tokyo, Japan
Built precisely at the triple intersection of three major tectonic plates - the North American Plate, the Philippine Plate and the Pacific Plate - Tokyo is constantly in motion. Long story and awareness of earthquakes pushed the city to create maximum levels of tectonic protection.

Tokyo is by far the city most prepared for earthquakes, which means we're probably underestimating the potential damage nature can cause.
Faced with a magnitude 8.9 earthquake, the strongest earthquake in Japanese history, Tokyo, 370 km from the epicenter, went into an automated shutdown mode: elevators stopped working, the subway stopped, people had to walk many kilometers in the cold night to get to their houses outside the city, where the greatest destruction occurred.
The 10-metre tsunami that followed the earthquake washed away hundreds of bodies on the north-east coast, leaving thousands of people missing.

Istanbul, Türkiye
Seismologists have long been monitoring the so-called “living” faults, one of which is the North Anatolian fault. It stretches for almost 1,000 kilometers - mainly through the territory of modern Turkey - and is located between the Eurasian and Anatolian plates. The shear rate in the area of ​​their contact reaches 13-20 mm/year, but the total amount of movement of these plates is higher - up to 30 mm/year. The city is a melting pot of rich and poor infrastructure, putting a huge portion of its 13 million residents at risk. In 1999, a magnitude 7.4 earthquake struck the city of Izmit, just 97 km from Istanbul.
While older buildings such as mosques survived, newer 20th-century buildings, often built from concrete mixed with salty groundwater and with disregard for local building codes, turned to dust. About 18,000 people died in the region.
In 1997, seismologists predicted that there was a 12% chance that the same earthquake could occur again in the region before 2026. Last year, seismologists published in the journal Nature Geoscience that the next earthquake would likely occur in the west of Izmit along the fault - dangerous 19 km south of Istanbul.

Seattle, Washington
When residents of the Pacific Northwest city think of disasters, two scenarios come to mind: a megaquake and the eruption of Mount Rainier.
In 2001, the Nisqually Indian Territory earthquake prompted the city to improve its earthquake preparedness plan, and several new improvements were made to building codes. However, many older buildings, bridges and roads have still not been updated to meet the new code.
The city lies on an active tectonic boundary along the North American Plate, the Pacific Plate, and the Juan de Fuca Plate. Ancient history Both earthquakes and tsunamis are recorded in the soil of the petrified flood forests, as well as in the oral histories passed down through generations of Pacific Northwest Native Americans.
Looming vaguely in the distance, and when the cloud cover is high enough, the impressive view of Mount Rainier reminds us that this is a dormant volcano and at any time it could push up Mount St. Helens as well.
Although seismologists are extremely good at monitoring volcanic tremors and warning authorities when an eruption is imminent - last year's eruption of Iceland's Eyjafjallajökull volcano showed that the extent and duration of the eruption is just anyone's guess. Most of the devastation will affect the east of the volcano.
But if an uncharacteristic northwest wind blows, the Seattle airport and the city itself will encounter large amounts of hot ash.

Los Angeles, California
Disasters are nothing new to the Los Angeles area - and not all of them are talked about on TV.
Over the past 700 years, powerful earthquakes have occurred in the region every 45-144 years. The last major earthquake with a magnitude of 7.9 occurred 153 years ago. In other words, Los Angeles is about to experience the next big earthquake.
Los Angeles, with a population of about 4 million, could experience strong tremors during the next major earthquake. According to some estimates, taking into account all of Southern California, with a population of about 37 million people, a natural disaster could kill between 2,000 and 50,000 people and cause billions of dollars in damage.

San Francisco, California
San Francisco, with a population of over 800,000, is another Big city on the West Coast of the United States, which could be devastated by a major earthquake and/or tsunami.
San Francisco is located near, although not exactly on the northern part of the San Andreas Fault. There are also several related faults running parallel across the San Francisco region, increasing the likelihood of an extremely destructive earthquake.
There has already been one such disaster in the history of the city. On April 18, 1906, San Francisco was hit by an earthquake measuring between 7.7 and 8.3. The disaster killed 3,000 people, caused half a billion dollars in damage and leveled much of the city.
In 2005, earthquake expert David Schwartz, a resident of San Francisco, estimated that there was a 62% chance that the region would experience a major earthquake within the next 30 years. Although some buildings in the city are built or reinforced to withstand an earthquake, many are still at risk, according to Schwartz. Residents are also advised to keep emergency kits with them at all times.

Being in continuous motion, they take direct participation in shaping the appearance of our planet. Tectonic plates are in continuous dynamics relative to each other, and even small deviations from the norm in their activity result in serious disasters: earthquakes, tsunamis, volcanic eruptions and the flooding of islands. Researchers began studying the most dangerous faults in the earth’s crust quite recently; to this day they cannot accurately determine in which place on the planet the next peak of tectonic activity will occur. The largest rifts are constantly monitored, but modern scientists know nothing about the existence of some dangerous tectonic faults.

The largest and most famous fault in the world is the San Andreas fault, a significant part of which runs on land. Its main part is located in California, and part of it runs along the coast. The length of the transform fault is about 1,300 meters; the rift was formed as a result of the destruction of the Farallon lithospheric plate. The giant fault is the cause of serious earthquakes, the magnitude of which reaches 8.1.

Strong earthquake occurred in San Francisco in 1906, and the last major Loma Prieta earthquake occurred in 1989. The maximum ground displacement that was recorded in the fault area during earthquakes was 7 meters. Over the past hundred years, the town of Santa Cruz, which is located in the immediate vicinity of San Francisco, has been severely damaged by numerous earthquakes. In 1989 alone, more than 18,000 houses were destroyed and 62 people died from the disaster.

The San Andreas fault is considered the most dangerous in the world; it is this fault, according to researchers, that can lead to a global catastrophe, followed by the death of civilization. Despite the destructive power of earthquakes, they help the fault release accumulated pressure and prevent a global catastrophe. It is impossible to accurately predict the time of the next earthquake; only recently have experts begun to track the vibrations of the plates that form the connector using GPS measurements. Currently, the fault section near Los Angeles is considered the most earthquake-prone. There have been no earthquakes here for a very long time, which means that the new earthquake promises to be incredibly powerful.