All movements of the earth's crust are called. Movement of the earth's crust

Structure earth's crust, geological structures, patterns of their location and development are studied by the section of geology - geotectonics. The discussion of crustal movements in this chapter is a presentation of intraplate tectonics. Movements of the earth's crust that cause changes in the occurrence of geological bodies are called tectonic movements.

A BRIEF SKETCH OF MODERN THEORY

PLATE TECTONICS

At the beginning of the 20th century. prof. Alfred Wegener put forward a hypothesis that served as the beginning of the development of a fundamentally new geological theory that describes the formation of continents and oceans on Earth. Currently, the mobilist theory of plate tectonics most accurately describes the structure of the Earth's upper geospheres, its development and the resulting geological processes and phenomena.

A simple and clear hypothesis of A. Wegener is that at the beginning of the Mesozoic, about 200 million years ago, all the continents that currently exist were grouped into a single supercontinent, called Pangea by A. Wegener. Pangea consisted of two large parts: northern - Laurasia, which included Europe, Asia (without Hindustan), North America, and southern - Gondwana, which included South America, Africa, Antarctica, Australia, Hindustan. These two parts of Pangea were almost separated by a deep gulf - a depression in the Tethys Ocean. The impetus for the creation of the continental drift hypothesis was the striking geometric similarity of the outlines of the coasts of Africa and South America, but then the hypothesis received some confirmation from paleontological, mineralogical, geological and structural studies. The weak point in A. Wegener’s hypothesis was the lack of explanations for the causes of continental drift, the identification of very significant forces capable of moving continents, these extremely massive geological formations.

The Dutch geophysicist F. Vening-Meines, the English geologist A. Holmes and the American geologist D. Griege first suggested the presence of convective flows in the mantle, which have colossal energy, and then connected it with the ideas of Wegener. In the middle of the 20th century. outstanding geological and geophysical discoveries were made: in particular, the presence of a global system of mid-ocean ridges (MORs) and rifts was established; the existence of a plastic layer of the asthenosphere was revealed; It was discovered that on Earth there are linear elongated belts in which 98% of all earthquake epicenters are concentrated and which border almost aseismic zones, later called lithospheric plates, as well as a number of other materials, which generally led to the conclusion that the prevailing “fixist” tectonic theory cannot explain, in particular, the identified paleomagnetic data on the geographical positions of the Earth's continents.

By the beginning of the 70s of the XX century. American geologist G. Hess and geophysicist R. Dietz, based on the discovery of the phenomenon of spreading (expansion) of the ocean floor, showed that due to the fact that hot, partially molten mantle matter, rising along rift cracks, should spread in different directions from the axis in the middle -ocean ridge and “push” the ocean floor in different directions, the raised mantle material fills the rift crack and, solidifying in it, builds up the diverging edges of the oceanic crust. Subsequent geological discoveries confirmed these positions. For example, it was found that the oldest age of the oceanic crust does not exceed 150-160 million years (this is only 1/30 of the age of our planet), modern rocks occur in rift cracks, and the most ancient rocks are as far away from the MOR as possible.

Currently, there are seven large plates in the upper shell of the Earth: Pacific, Eurasian, Indo-Australian, Antarctic, African, North and South American; seven medium-sized plates, for example, Arabian, Nazca, Coconut, etc. Within large plates, independent plates or blocks of medium size and many small ones are sometimes distinguished. All plates move relative to each other, so their boundaries are clearly marked as zones of increased seismicity.

In general, there are three types of movement of plates: moving apart with the formation of rifts, compression or thrusting (submerging) of one plate onto another, and, finally, sliding or shifting of plates relative to each other. All these movements of lithospheric plates along the surface of the asthenosphere occur under the influence of convective currents in the mantle. The process of pushing an oceanic plate under a continental one is called subduction (for example, the Pacific “subducts” under the Eurasian in the area of ​​the Japanese island arc), and the process of pushing an oceanic plate onto a continental plate is called obduction. In ancient times, such a process of continental collision (collision) led to the closure of the Tethys Ocean and the emergence of the Alpine-Himalayan mountain belt.

The use of Euler's theorem on the movement of lithospheric plates on the surface of the geoid with the use of data from space and geophysical observations made it possible to calculate (J. Minster) the rate of removal of Australia from Antarctica - 70 mm/year, South America from Africa - 40 mm/year; North America from Europe - 23 mm/year.

The Red Sea is expanding at 15 mm/year, and Hindustan collides with Eurasia at a rate of 50 mm/year. Despite the fact that the global theory of plate tectonics is sound both mathematically and physically, many geological questions are not yet fully understood; these are, for example, the problems of intraplate tectonics: upon detailed study, it turns out that lithospheric plates are by no means absolutely rigid, unformable and monolithic; according to the works of a number of scientists, powerful flows of mantle matter rise from the bowels of the Earth, capable of heating, melting and deforming the lithospheric plate (J. Wilson). A significant contribution to the development of the most modern tectonic theory was made by Russian scientists V.E. Hein, P.I. Kropotkin, A.V. Peive, O.G. Sorokhtin, S.A. Ushakov and others.

TECTONIC MOVEMENTS

This discussion of tectonic movements is most applicable to intraplate tectonics, with some generalizations.

Tectonic movements in the earth's crust occur constantly. In some cases they are slow, barely noticeable to the human eye (eras of peace), in others - in the form of intense stormy processes (tectonic revolutions). There have been several such tectonic revolutions in the history of the earth's crust.

The mobility of the earth's crust largely depends on the nature of its tectonic structures. The largest structures are platforms and geosynclines. Platforms refer to stable, rigid, sedentary structures. They are characterized by leveled relief forms. From below, they consist of a rigid section of the earth’s crust that cannot be folded (crystalline basement), above which lies a horizontal layer of undisturbed sedimentary rocks. Typical examples of ancient platforms are the Russian and Siberian. Platforms are characterized by calm, slow movements of a vertical nature. As opposed to platforms geosynclines They are moving parts of the earth's crust. They are located between the platforms and represent, as it were, their movable joints. Geosynclines are characterized by various tectonic movements, volcanism, and seismic phenomena. In the zone of geosynclines, intensive accumulation of thick strata of sedimentary rocks occurs.

Tectonic movements of the earth's crust can be divided into three main types:

• oscillatory, expressed in the slow rise and fall of individual sections of the earth’s crust and leading to the formation of large uplifts and troughs;
• folded, causing the horizontal layers of the earth's crust to collapse into folds;
• discontinuous, leading to ruptures of layers and arrays rocks.

Oscillatory movements. Certain sections of the earth's crust rise over many centuries, while others fall at the same time. Over time, the rise gives way to a fall, and vice versa. Oscillatory movements do not change the original conditions of occurrence of rocks, but their engineering and geological significance is enormous. The position of the boundaries between land and seas, shallowing and increased erosive activity of rivers, the formation of relief and much more depend on them.

The following types of oscillatory movements of the earth's crust are distinguished: 1) past geological periods; 2) the latest, associated with the Quaternary period; 3) modern.

Of particular interest to engineering geology are modern oscillatory movements that cause changes in the heights of the earth's surface in a given area. To reliably estimate the rate of their manifestation, they use geodetic work high precision. Modern oscillatory movements occur most intensely in areas of geosynclines. It has been established, for example, that during the period from 1920 to 1940. The Donetsk basin rose relative to the city of Rostov-on-Don at a rate of 6-10 mm/year, and the Central Russian Upland - up to 15-20 mm/year. The average rates of modern subsidence in the Azov-Kuban depression are 3-5, and in the Terek depression - 5-7 mm/year. Thus, the annual speed of modern oscillatory movements is most often equal to several millimeters, and 10-20 mm/year is a very high speed. The known limiting speed is slightly more than 30 mm/year.

In Russia, the areas of Kursk (3.6 mm/year), the island of Novaya Zemlya, and the Northern Caspian Sea are rising. A number of areas of European territory continue to sink - Moscow (3.7 mm/year), St. Petersburg (3.6 mm/year). The Eastern Ciscaucasia is sinking (5-7 mm/year). There are numerous examples of vibrations of the earth's surface in other countries. For many centuries, areas of Holland (40-60 mm/year), the Danish Straits (15-20 mm/year), France and Bavaria (30 mm/year) have been intensively subsiding. Scandinavia continues to rise intensively (25 mm/year), only the Stockholm region has risen by 190 mm over the past 50 years.

Due to the lowering of the western coast of Africa, the estuarine part of the river bed. The Congo has sank and can be traced on the ocean floor to a depth of 2000 m at a distance of 130 km from the coast.

Modern tectonic movements of the earth's crust are studied by science neotectonics. Modern oscillatory movements must be taken into account when constructing hydraulic structures such as reservoirs, dams, reclamation systems, cities near the sea. For example, lowering the area Black Sea coast leads to intense erosion of coastlines by sea waves and the formation of large landslides.

Folding movements. Sedimentary rocks initially lie horizontally or nearly horizontally. This position is maintained even with oscillatory movements of the earth's crust. Folded tectonic movements remove layers from a horizontal position, give them a slope or crush them into folds. This is how folded dislocations arise (Fig. 31).

All forms of folded dislocations are formed without breaking the continuity of layers (layers). It's theirs characteristic feature. The main ones among these dislocations are: monocline,

flexure, anticline and syncline.

Monocline is the simplest form of disturbance of the original occurrence of rocks and is expressed in the general inclination of the layers in one direction (Fig. 32).

Flexure- a knee-like fold formed when one part of the rock mass is displaced relative to another without breaking the continuity.

Anticline- a fold facing upward with its apex (Fig. 33), and syncline- a fold with the apex facing down (Fig. 34, 35). The sides of the folds are called wings, the tops are called locks, and inner part- core.

It should be noted that rocks at the tops of folds are always fissured, and sometimes even crushed (Fig. 36).

Breaking movements. As a result of intense tectonic movements, ruptures in the continuity of layers can occur. The broken parts of the layers shift relative to each other. The displacement occurs along the rupture plane, which manifests itself in the form of a crack. The magnitude of the displacement amplitude varies - from centimeters to kilometers. Fault dislocations include normal faults, reverse faults, horsts, grabens and thrusts (Fig. 37).

Reset is formed as a result of the lowering of one part of the thickness relative to another (Fig. 38, A). If an uplift occurs during a rupture, a reverse fault is formed (Fig. 38, b). Sometimes several gaps form in one area. In this case, stepped faults (or reverse faults) arise (Fig. 39).

Rice. 31.

/ - full (normal); 2- isoclinic; 3- chest; 4- straight; 5 - oblique; 6 - inclined; 7- recumbent; 8- overturned; 9- flexure; 10 - monoclinic

Rice. 32.

situation

Rice. 33.

(according to M. Vasic)

Rice. 34. Full fold ( A) and fold elements (b):

1 - anticline; 2 - syncline

Rice. 35. Synclinal occurrence of layers of sedimentary rocks in a natural environment (a fault is visible in the axis of the fold)

Rice. 37.

A - reset; b- step reset; V - uplift; G- thrust; d- graben; e- horst; 1 - stationary part of the thickness; 2-offset part; P - surface of the Earth; p - rupture plane

Shear surface

Rice. 38. Scheme of shift of layered thickness: A - two moved blocks; b - profile with a characteristic shift of rocks (according to M. Vasich)

Dropped block

Rhineland

Rice. 39.

Rice. 40.

A - normal; b- reserve; V- horizontal

Rice. 41.

A - separation; b - brittle chipping; V- formation of pinch; G- viscous spalling at

stretching (“unlensing”)

Graben occurs when a section of the Earth's crust sinks between two large faults. In this way, for example, Lake Baikal was formed. Some experts consider Baikal to be the beginning of the formation of a new rift.

Horst- the shape opposite to the graben.

Thrust in contrast to previous forms, discontinuous dislocations occur when thicknesses are displaced in a horizontal or relatively inclined plane (Fig. 40). As a result of thrusting, young deposits can be overlain by rocks of an older age (Fig. 41, 42, 43).

Occurrence of layers. When studying the engineering-geological conditions of construction sites, it is necessary to establish the spatial position of the layers. Determining the position of layers (layers) in space makes it possible to solve issues of depth, thickness and nature of their occurrence, makes it possible to select layers as the foundations of structures, estimate groundwater reserves, etc.

The importance of dislocations for engineering geology. For construction purposes the most favorable conditions are hot

Rice. 42. Eastern end of the Audiberge thrust (Alpes-Maritimes). Incision (A) depicts the structure of the right bank of the Lu Valley, located directly behind the site shown in the block diagram (b); the cut is oriented in the opposite direction. The thrust amplitude, corresponding to the magnitude of the displacement of layers in the upturned wing of the anticline, gradually decreases from west to east

zonal occurrence of layers, their large thickness, homogeneity of composition. In this case, buildings and structures are located in a homogeneous soil environment, creating the prerequisite for uniform compressibility of the layers under the weight of the structure. In such conditions, structures obtain the greatest stability (Fig. 44).

Rice. 43.

Levan Fault in the Lower Alps

Rice. 44.

a, b - sites favorable for construction; V- unfavorable; G - unfavorable; L- structure (building)

The presence of dislocations complicates the engineering and geological conditions of construction sites - the homogeneity of the soils of the foundations of structures is disrupted, crushing zones are formed, the strength of the soil decreases, displacements periodically occur along the fracture cracks, and groundwater circulates. When the layers are steeply dipping, the structure can be located simultaneously on different soils, which sometimes leads to uneven compressibility of the layers and deformation of the structures. For buildings unfavorable condition is the complex nature of the folds. It is not advisable to locate structures on fault lines.

SEISMIC PHENOMENA

Seismic(from the Greek - shaking) phenomena manifest themselves in the form of elastic vibrations of the earth's crust. This formidable natural phenomenon is typical of geosyncline areas where modern mountain-building processes are active, as well as subduction and obduction zones.

Tremors of seismic origin occur almost continuously. Special instruments record more than 100 thousand earthquakes during the year, but, fortunately, only about 100 of them lead to destructive consequences and some lead to disasters with the loss of life and massive destruction of buildings and structures (Fig. 45).

Earthquakes also arise during volcanic eruptions (in Russia, for example, in Kamchatka), the occurrence of failures due to the collapse of rocks into large underground caves,

Rice. 45.

ry, narrow deep valleys, and also as a result of powerful explosions carried out, for example, for construction purposes. The destructive effect of such earthquakes is small and they are of local significance, and the most destructive are tectonic seismic phenomena, which, as a rule, cover large areas.

History knows catastrophic earthquakes when tens of thousands of people died and entire cities or most of them were destroyed (Lisbon - 1755, Tokyo - 1923, San Francisco - 1906, Chile and the island of Sicily - 1968). Only in the first half of the 20th century. there were 3,749 of them, with 300 earthquakes occurring in the Baikal region alone. The most destructive ones were in the cities of Ashgabat (1948) and Tashkent (1966).

An exceptionally powerful catastrophic earthquake occurred on December 4, 1956 in Mongolia, which was also recorded in China and Russia. It was accompanied by enormous destruction. One of the mountain peaks split in half, part of a mountain 400 m high collapsed into a gorge. A fault depression up to 18 km long and 800 m wide was formed. Cracks up to 20 m wide appeared on the surface of the earth. The main one of these cracks stretched up to 250 km.

The most catastrophic earthquake was the 1976 earthquake that occurred in Tangshan (China), as a result of which 250 thousand people died, mainly under collapsed buildings made of clay (mud brick).

Tectonic seismic phenomena occur both at the bottom of the oceans and on land. In this regard, seaquakes and earthquakes are distinguished.

Seaquakes arise in deep oceanic depressions of the Pacific, and less commonly, the Indian and Atlantic oceans. Rapid rises and falls of the ocean floor cause displacement of large masses of rocks and generate gentle waves (tsunamis) on the ocean surface with a distance between crests of up to 150 km and a very small height above the great depths of the ocean. When approaching the shore, along with the rise of the bottom, and sometimes the narrowing of the shores in the bays, the height of the waves increases to 15-20 m and even 40 m.

Tsunami move over distances of hundreds and thousands of kilometers at speeds of 500-800 and even more than 1000 km/h. As the depth of the sea decreases, the steepness of the waves increases sharply and they crash onto the shores with terrible force, causing the destruction of structures and the death of people. During the sea earthquake of 1896 in Japan, waves 30 m high were recorded. As a result of hitting the shore, they destroyed 10,500 houses, killing more than 27 thousand people.

The Japanese, Indonesian, Philippine and Hawaiian islands, as well as the Pacific coast of South America, are most often affected by tsunamis. In Russia, this phenomenon is observed on the eastern shores of Kamchatka and the Kuril Islands. The last catastrophic tsunami in this area occurred in November 1952 in the Pacific Ocean, 140 km from the coast. Before the wave arrived, the sea retreated from the coast to a distance of 500 m, and 40 minutes later a tsunami with sand, silt and various debris hit the coast. This was followed by a second wave up to 10-15 m high, which completed the destruction of all buildings located below the ten-meter mark.

The highest seismic wave - a tsunami - rose off the coast of Alaska in 1964; its height reached 66 m, and its speed was 585 km/h.

The frequency of tsunamis is not as high as that of earthquakes. Thus, over 200 years, only 14 of them were observed on the coast of Kamchatka and the Kuril Islands, of which four were catastrophic.

On the Pacific coast in Russia and other countries, special observation services have been created that warn of the approach of a tsunami. This allows you to warn and protect people from danger in time. Built to combat tsunamis engineering structures in the form of protective embankments, reinforced concrete piers, wave walls, artificial shallows are created. Buildings are placed on a high part of the terrain.

Earthquakes. Seismic waves. The source of generation of seismic waves is called the hypocenter (Fig. 46). Based on the depth of the hypocenter, earthquakes are distinguished: surface - from 1 to 10 km depth, crustal - 30-50 km and deep (or plutonic) - from 100-300 to 700 km. The latter are already in the Earth's mantle and are associated with movements occurring in the deep zones of the planet. Such earthquakes were observed in the Far East, Spain and Afghanistan. The most destructive are surface and crustal earthquakes.

Rice. 46. Hypocenter (H), epicenter (Ep) and seismic waves:

1 - longitudinal; 2- transverse; 3 - superficial

Directly above the hypocenter on the surface of the earth is located epicenter. In this area, surface shaking occurs first and with greatest strength. An analysis of earthquakes has shown that in seismically active regions of the Earth, 70% of the sources of seismic phenomena are located to a depth of 60 km, but the most seismic depth is still from 30 to 60 km.

Seismic waves, which by their nature are elastic vibrations, emanate from the hypocenter in all directions. Longitudinal and transverse seismic waves are distinguished as elastic vibrations propagating in the ground from the sources of earthquakes, explosions, impacts and other sources of excitation. Seismic waves - longitudinal, or R- waves (lat. primae- the first), come to the surface of the earth first, since they have a speed 1.7 times greater than transverse waves; transverse, or 5-waves (lat. secondae- second), and superficial, or L- waves (lat. 1op-qeg- long). Lengths There are more L waves, and the speed is less than that of R- and 5-waves. Longitudinal seismic waves are compression and tension waves of the medium in the direction of seismic rays (in all directions from the source of the earthquake or other source of excitation); transverse seismic waves - shear waves in the direction perpendicular to the seismic rays; surface seismic waves are waves propagating along the surface of the earth. L-waves are divided into Love waves (transverse oscillations in the horizontal plane without a vertical component) and Rayleigh waves (complex oscillations with a vertical component), named after the scientists who discovered them. Of greatest interest to a civil engineer are longitudinal and transverse waves. Longitudinal waves cause expansion and compression of rocks in the direction of their movement. They spread in all media - solid, liquid and gaseous. Their speed depends on the substance of the rocks. This can be seen from the examples given in table. 11. Transverse vibrations are perpendicular to longitudinal vibrations, propagate only in a solid medium and cause shear deformation in rocks. The speed of transverse waves is approximately 1.7 times less than that of longitudinal waves.

On the surface of the earth, waves of a special kind diverge from the epicenter in all directions - surface waves, which by their nature are waves of gravity (like sea swells). The speed of their spread is lower than that of transverse ones, but they have an equally detrimental effect on structures.

The action of seismic waves, or, in other words, the duration of earthquakes, usually manifests itself within a few seconds, less often minutes. Sometimes long-lasting earthquakes occur. For example, in Kamchatka in 1923, the earthquake lasted from February to April (195 tremors).

Table 11

Velocity of propagation of longitudinal (y p) and transverse (y 5) waves

V various breeds and in water, km/sec

Estimation of earthquake strength. Earthquakes are constantly monitored using special devices- seismographs, which allow qualitative and quantitative assessment of the strength of earthquakes.

Seismic scales (gr. earthquake + lat. .?sd-

• 1a - ladder) is used to estimate the intensity of vibrations (shocks) on the Earth's surface during earthquakes in points. The first (close to modern) 10-point seismic scale was compiled in 1883 jointly by M. Rossi (Italy) and F. Forel (Switzerland). Currently, most countries in the world use 12-point seismic scales: “MM” in the USA (improved Mercalli-Konkani-Zieberg scale); International MBK-64 (named after the authors S. Medvedev, V. Shpohnheuer, V. Karnik, created in 1964); Institute of Physics of the Earth, USSR Academy of Sciences, etc. In Japan, a 7-point scale is used, compiled by F. Omori (1900) and subsequently revised many times. The score on the MBK-64 scale (refined and supplemented by the Interdepartmental Council on Seismology and Earthquake-Resistant Construction in 1973) is established:
  • on the behavior of people and objects (from 2 to 9 points);
  • according to the degree of damage or destruction of buildings and structures (from 6 to 10 points);
  • on seismic deformations and the occurrence of other natural processes and phenomena (from 7 to 12 points).

Very famous is the Richter scale, proposed in 1935 by the American seismologist C.F. Richter, theoretically substantiated together with B. Gutenberg in 1941-1945. magnitude scale(M); refined in 1962 (Moscow-Prague scale) and recommended by the International Association of Seismology and Physics of the Earth's Interior as standard. On this scale, the magnitude of any earthquake is defined as the decimal logarithm of the maximum amplitude of the seismic wave (expressed in micrometers) recorded by a standard seismograph at a distance of 100 km from the epicenter. At other distances from the epicenter to the seismic station, a correction is introduced to the measured amplitude in order to bring it to the one that corresponds to the standard distance. The zero of the Richter scale (M = 0) gives a focus at which the amplitude of the seismic wave at a distance of 100 km from the epicenter will be equal to 1 μm, or 0.001 mm. When the amplitude increases by 10 times, the magnitude increases by one. When the amplitude is less than 1 μm, the magnitude has negative values; known maximum magnitude values ​​M = 8.5...9. Magnitude - calculated value, relative characteristic of the seismic source, independent of the location of the recording station; used to estimate the total energy released in the source (a functional relationship between magnitude and energy has been established).

The energy released in the source can be expressed absolute value (E, J), energy class value (K = \%E) or a conventional quantity called magnitude,

TO-5 K=4

M =--g--. Magnitude of the largest earthquakes

M = 8.5...8.6, which corresponds to an energy release of 10 17 -10 18 J or seventeenth - eighteenth energy classes. The intensity of earthquakes on the earth's surface (surface shaking) is determined using seismic intensity scales and assessed in conventional units - points. Severity (/) is a function of magnitude (M), focal depth (AND) and the distance from the point in question to the epicenter SCH:

I = 1.5M+3.518 l/1 2 +And 2 +3.

Below are comparative characteristics different groups of earthquakes (Table 12).

Comparative characteristics of earthquakes

To calculate the force effects (seismic loads) exerted by earthquakes on buildings and structures, the following concepts are used: vibration acceleration (A), seismicity coefficient ( To c) and maximum relative displacement (ABOUT).

In practice, the strength of earthquakes is measured in points. In Russia, a 12-point scale is used. Each point corresponds to a certain value of vibration acceleration A(mm/s 2). In table 13 shows a modern 12-point scale and gives a brief description of consequences of earthquakes.

Seismic points and consequences of earthquakes

Table 13

Seismic regions of Russia. The entire earth's surface is divided into zones: seismic, aseismic and peneseismic. TO seismic include areas that are located in geosynclinal areas. IN aseismic There are no earthquakes in areas (Russian Plain, Western and Northern Siberia). IN peneseismic In these areas, earthquakes occur relatively rarely and are of low magnitude.

For the territory of Russia, a map of the distribution of earthquakes has been compiled, indicating the points. Seismic regions include the Caucasus, Altai, Transbaikalia, Far East, Sakhalin, Kuril Islands, Kamchatka. These areas occupy a fifth of the territory on which they are located big cities. This map is currently being updated and will contain information on the frequency of earthquakes over time.

Earthquakes contribute to the development of extremely dangerous gravitational processes - landslides, collapses, and screes. As a rule, all earthquakes of magnitude seven and above are accompanied by these phenomena, and of a catastrophic nature. The widespread development of landslides and landslides was observed, for example, during the Ashgabat earthquake (1948), a strong earthquake in Dagestan (1970), in the Chkhalta valley in the Caucasus (1963), before

Line R. Naryn (1946), when seismic vibrations unbalanced large massifs of weathered and destroyed rocks that were located in the upper parts of high slopes, which caused damming of rivers and the formation of large mountain lakes. Weak earthquakes also have a significant impact on the development of landslides. In these cases they are like a push, trigger a massif already prepared for collapse. So, on the right slope of the river valley. Aktury in Kyrgyzstan after the earthquake in October 1970, three extensive landslides formed. Often, it is not so much the earthquakes themselves that affect buildings and structures as the landslide and landslide phenomena they cause (Karateginskoe, 1907, Sarez, 1911, Faizabad, 1943, Khaitskoe, 1949 earthquakes). The mass volume of the seismic collapse (collapse - collapse), located in the Babkha seismic structure (northern slope of the Khamar-Daban ridge, Eastern Siberia), is about 20 million m 3. The Sarez earthquake with a magnitude of 9, which occurred in February 1911, threw off the right bank of the river. Murghab at the confluence of the Usoy Darya with 2.2 billion m 3 of rock mass, which led to the formation of a dam 600-700 m high, 4 km wide, 6 km long and a lake at an altitude of 3329 m above sea level with a volume of 17-18 km 3, with a mirror area of ​​86.5 km 2, 75 km long, up to 3.4 km wide, 190 m deep. A small village was under the rubble, and the village of Sarez was under water.

As a result of the seismic impact during the Khait earthquake (Tajikistan, July 10, 1949) with a magnitude of 10 points, landslide and landslide phenomena on the slope of the Takhti ridge developed greatly, after which earth avalanches and mudflows of 70 meters thickness were formed at a speed of 30 m/s. The volume of the mudflow is 140 million m3, the area of ​​destruction is 1500 km2.

Construction in seismic areas(seismic microzoning). At construction work in earthquake areas, it is necessary to remember that seismic map scores characterize only some average soil conditions of the area and therefore do not reflect the specific geological features of a particular construction site. These points are subject to clarification based on a specific study of the geological and hydrogeological conditions of the construction site (Table 14). This is achieved by increasing the initial scores obtained from the seismic map by one for areas composed of loose rocks, especially wet ones, and decreasing them by one for areas composed of strong rocks. Rocks of category II in terms of seismic properties retain their original value unchanged.

Adjustment of scores of seismic areas based on engineering-geological and hydrogeological data

The adjustment of construction site scores is valid mainly for flat or hilly areas. For mountainous areas, other factors must be taken into account. Areas with highly dissected relief, river banks, slopes of ravines and gorges, landslides and karst areas are dangerous for construction. Areas located near tectonic faults are extremely dangerous. It is very difficult to build when the groundwater level is high (1-3 m). It should be taken into account that the greatest destruction during earthquakes occurs in wetlands, in waterlogged silty, and in under-compacted loess rocks, which during seismic shaking are vigorously compacted, destroying buildings and structures built on them.

When conducting engineering-geological surveys in seismic areas, it is necessary to perform additional work regulated by the relevant section of SNiP 11.02-96 and SP 11.105-97.

In areas where the magnitude of earthquakes does not exceed magnitude 7, the foundations of buildings and structures are designed without taking into account seismicity. In seismic areas, i.e. areas with a calculated seismicity of 7, 8 and 9 points, the design of foundations is carried out in accordance with the chapter of the special SNiP for the design of buildings and structures in seismic areas.

In seismic areas, it is not recommended to lay water pipelines, main lines and sewer collectors in water-saturated soils (except for rocky, semi-rocky and coarse-clastic soils), in bulk soils, regardless of their moisture content, as well as in areas with tectonic disturbances. If the main source of water supply is groundwater from fractured and karst rocks, surface water bodies should always serve as an additional source.

Predicting the moment of the onset of an earthquake and its strength is of great practical importance for human life and industrial activity. There have already been noticeable successes in this work, but in general the problem of earthquake prediction is still at the development stage.

Volcanism is the process of magma breaking out from the depths of the earth's crust to the surface of the earth. Volcanoes- geological formations in the form of mountains and elevations of cone-shaped, oval and other shapes that arose in places where magma broke out onto the earth’s surface.

Volcanism manifests itself in areas of subduction and obduction, and within lithospheric plates - in zones of geosynclines. Largest quantity volcanoes are located along the coasts of Asia and America, on the islands of the Pacific and Indian oceans. There are also volcanoes on some islands of the Atlantic Ocean (off the coast of America), in Antarctica and Africa, in Europe (Italy and Iceland). There are active and extinct volcanoes. Active are those volcanoes that erupt constantly or periodically; extinct- those that have ceased to operate, and there is no data on their eruptions. In some cases, extinct volcanoes resume their activity again. This was the case with Vesuvius, which unexpectedly erupted in 79 AD. e.

On the territory of Russia, volcanoes are known in Kamchatka and the Kuril Islands (Fig. 47). There are 129 volcanoes in Kamchatka, of which 28 are active. The most famous volcano is Klyuchevskaya Sopka (height 4850 m), the eruption of which repeats approximately every 7-8 years. Avachinsky, Karymsky, and Bezymyansky volcanoes are active. There are up to 20 volcanoes on the Kuril Islands, about half of which are active.

Extinct volcanoes in the Caucasus - Kazbek, Elbrus, Ararat. Kazbek, for example, was still active at the beginning of the Quaternary period. Its lavas cover the area of ​​the Georgian Military Road in many places.

In Siberia, extinct volcanoes have also been discovered within the Vitim Highlands.

Rice. 47.

Volcanic eruptions occur in different ways. This largely depends on the type of magma that is erupting. Acidic and intermediate magmas, being very viscous, erupt with explosions, throwing out stones and ash. The outpouring of mafic magma usually occurs calmly, without explosions. In Kamchatka and the Kuril Islands, volcanic eruptions begin with tremors, followed by explosions with the release of water vapor and the outpouring of hot lava.

The eruption, for example, of Klyuchevskaya Sopka in 1944-1945. was accompanied by the formation of a hot cone up to 1500 m high above the crater, the release of hot gases and rock fragments. After this, an outpouring of lava occurred. The eruption was accompanied by a magnitude 5 earthquake. When volcanoes like Vesuvius erupt, heavy rainfall occurs due to the condensation of water vapor. Mud flows of exceptional strength and magnitude arise, which, rushing down the slopes, bring enormous destruction and devastation. Water formed as a result of melting snow on the volcanic slopes of craters can also act; and the water of lakes formed on the site of the crater.

The construction of buildings and structures in volcanic areas has certain difficulties. Earthquakes usually do not reach destructive force, but the products released by a volcano can adversely affect the integrity of buildings and structures and their stability.

Many gases released during eruptions, such as sulfur dioxide, are dangerous to people. Condensation of water vapor causes catastrophic rainfall and mud flows. Lava forms streams, the width and length of which depend on the slope and topography of the area. There are known cases when the length of the lava flow reached 80 km (Iceland), and the thickness was 10-50 m. The flow speed of the main lavas is 30 km/h, acid lavas - 5-7 km/h, volcanic ash (silt particles) fly up from the volcanoes. , sand, lapilli (particles 1-3 cm in diameter), bombs (from centimeters to several meters). They all represent solidified lava and during a volcanic eruption, they scatter to various distances, cover the surface of the earth with a multi-meter layer of debris, and collapse the roofs of buildings.

The earth's crust consists of lithospheric plates. Each lithospheric plate is characterized by continuous movement. People don't notice such movements because they happen extremely slowly.

Causes and consequences of crustal movement

We all know that our planet consists of three parts: the earth's core, the earth's mantle, and the earth's crust. At the core of our planet are concentrated many chemical substances, which continuously enter into a chemical reaction with each other.

As a result of such chemical, radioactive and thermal reactions, vibrations occur in the lithosphere. Due to this, the earth's crust can move vertically and horizontally.

History of the study of crustal movements

Tectonic movements were studied by ancient scientists. The ancient Greek geographer Strabo first proposed the theory that individual areas of land are systematically rising. The famous Russian scientist Lomonosov called the movements of the earth's crust as long-term and insensitive earthquakes.

However, more detailed study processes of movement of the earth's crust began at the end of the 19th century. American geologist Gilbert classified movements of the earth's crust into two main types: those that create mountains (orogenic) and those that create continents (epeirogenic). Both foreign and domestic scientists studied the movement of the earth's crust, in particular: V. Belousov, Yu. Kosygin, M. Tetyaev, E. Haarman, G. Stille.

Types of crustal movement

There are two types of tectonic movements: vertical and horizontal. Vertical movements are called radial. Such movements are expressed in the systematic raising (or lowering) of lithospheric plates. Often, radial movements of the earth's crust occur as a consequence of strong earthquakes.

Horizontal movements represent displacements of lithospheric plates. According to many modern scientists, all existing continents were formed as a result of horizontal displacement of lithospheric plates.

The significance of the movement of the earth's crust for humans

Movements of the earth's crust today threaten the lives of many people. A striking example is the Italian city of Venice. The city is located on a section of the lithospheric plate, which high speed settles.

Every year, the city sinks under water - a process of transgression occurs (long-term offensive sea ​​water to land). There are cases in history when, due to the movement of the earth's crust, cities and towns went under water, and after some time they rose again (the process of regression).

Tectonic movements are movements of the earth's crust associated with internal forces in the earth's crust and mantle.Branch of Geology, which studies these movements, as well as the modern structure and development of the structural elements of the earth's crust is called tectonics.

The largest structural elements of the earth's crust are platforms, geosynclines and oceanic plates.

Platforms are huge, relatively stationary, stable sections of the earth's crust. The platforms are characterized by a two-tier structure. The lower, more ancient tier (crystalline basement) is composed of sedimentary rocks, crushed into folds, or igneous rocks subjected to metamorphism. Upper tier(platform cover) consists almost entirely of horizontally occurring sedimentary rocks.

Classic examples of platform areas are the East European (Russian) platform, West Siberian, Turanian and Siberian, which occupy vast spaces. The North African, Indian and other platforms are also known in the world.

The thickness of the upper tier of the platforms reaches 1.5-2.0 km or more. The section of the earth's crust where the upper layer is absent and the crystalline foundation extends directly to the outer surface is called shields (Baltic, Voronezh, Ukrainian, etc.).

Within platforms, tectonic movements are expressed in the form of slow vertical oscillatory movements of the earth's crust. Volcanism and seismic movements (earthquakes) are poorly developed or completely absent. The relief of the platforms is closely related to the deep structure of the earth's crust and is expressed mainly in the form of vast plains (lowlands).

Geosynclines are the most mobile, linearly elongated sections of the earth's crust, framing platforms. On early stages In their development, they are characterized by intense dives, and in the final stages – by impulsive rises.

Geosynclinal regions are the Alps, Carpathians, Crimea, Caucasus, Pamirs, Himalayas, the Pacific coastline and other folded mountain structures. All these areas are characterized by active tectonic movements, high seismicity and volcanism. In these same areas, powerful magmatic processes are actively developing with the formation of effusive lava covers and flows and intrusive bodies (stocks, etc.). In Northern Eurasia, the most mobile and seismically active region is the Kuril-Kamchatka zone.

Oceanic plates are the largest tectonic structures in the earth's crust and form the basis of the ocean floors. Unlike continents, oceanic plates have not been studied enough, which is associated with significant difficulties in obtaining geological information about their structure and composition of matter.

The following main tectonic movements of the earth's crust are distinguished:

- oscillatory;

- folded;

- explosive.

Oscillatory tectonic movements manifest themselves in the form of slow uneven uplifts and lowerings of individual sections of the earth's crust. The oscillatory nature of their movement lies in the change in its sign: uplift in some geological epochs is replaced by lowering in others. Tectonic movements of this type occur continuously and everywhere. There are no tectonically stationary sections of the earth's crust on the earth's surface - some rise, others fall.

According to the time of their manifestation, oscillatory movements are divided into modern (last 5-7 thousand years), newest (Neogene and Quaternary periods) and movements of past geological periods.

Modern oscillatory movements are studied at special testing sites using repeated geodetic observations using the method of high-precision leveling. More ancient oscillatory movements are judged by the alternation of marine and continental sediments and a number of other signs.

The rate of rise or fall of individual sections of the earth's crust varies widely and can reach 10-20 mm per year or more. For example, South coast The North Sea in Holland drops by 5-7 mm per year. Holland is saved from the invasion of the sea onto land (transgression) by dams up to 15 m high, which are constantly being built up. At the same time, in nearby areas in Northern Sweden in the coastal zone, modern uplifts of the earth's crust of up to 10-12 mm per year are observed. In these areas, part of the port facilities turned out to be remote from the sea due to its retreat from the coast (regression).

Geodetic observations carried out in the areas of the Black, Caspian and Azov Seas showed that the Caspian Lowland, the eastern coast of the Akhzov Sea, the depressions at the mouths of the Terek and Kuban rivers, and the northwestern coast of the Black Sea are sinking at a rate of 2-4 mm per year. As a consequence, transgression is observed in these areas, i.e. advance of the sea onto land. On the contrary, land areas on the coast experience slow uplifts Baltic Sea, as well as, for example, the regions of Kursk, the mountain regions of Altai, Sayan, New land etc. Other areas continue to sink: Moscow (3.7 mm/year), St. Petersburg (3.6 mm/year), etc.

The greatest intensity of oscillatory movements of the earth's crust is observed in geosynclinal areas, and the lowest in platform areas.

The geological significance of oscillatory movements is enormous. They determine the conditions of sedimentation, the position of the boundaries between land and sea, shallowing or increased erosive activity of rivers. Oscillatory movements that occurred in recent times (Neogene-Quaternary period) had a decisive influence on the formation of the modern topography of the Earth.

Oscillatory (modern) movements must be taken into account when constructing hydraulic structures such as reservoirs, dams, shipping canals, cities by the sea, etc.

Fold tectonic movements. In geosynclinal areas, tectonic movements can significantly disrupt the original form of rock formation. Disturbances in the forms of the primary occurrence of rocks caused by the tectonic movement of the earth's crust are called dislocations. They are divided into folded and discontinuous.

Folded dislocations can be in the form of elongated linear folds or expressed in a general tilt of the layers in one direction.

An anticline is an elongated linear fold, convexly facing upward. In the core (center) of the anticline there are more ancient layers, on the wings of the folds there are younger ones.

A syncline is a fold similar to an anticline, but convexly directed downwards. The core of the syncline contains younger layers than those on the wings.

Monocline - is a thickness of rock layers inclined in one direction at the same angle.

Flexure is a knee-shaped fold with a stepwise bending of layers.

The orientation of layers in a monoclinal occurrence is characterized using the strike line, dip line and dip angle.

Rupture tectonic movements. They lead to disruption of the continuity of rocks and their rupture along any surface. Fractures in rocks occur when stresses in the earth's crust exceed the tensile strength of rocks.

Fault dislocations include normal faults, reverse faults, thrusts, strike-slip faults, grabens and horsts.

Reset– is formed as a result of the lowering of one part of the thickness relative to another.

Reverse fault - formed when one part of the strata rises relative to another.

Thrust – displacement of rock blocks along an inclined fault surface.

Shear is the displacement of rock blocks in the horizontal direction.

A graben is a section of the earth’s crust bounded by tectonic faults (faults) and descended along them relative to adjacent sections.

An example of large grabens is the depression of Lake Baikal and the valley of the Rhine River.

Horst is an elevated section of the earth's crust, bounded by faults or reverse faults.

Disruptive tectonic movements are often accompanied by the formation of various tectonic cracks, which are characterized by their capture of thick rock strata, consistency of orientation, the presence of traces of displacement and other signs.

A special type of discontinuous tectonic faults are deep faults that divide the earth's crust into separate large blocks. Deep faults have a length of hundreds and thousands of kilometers and a depth of more than 300 km. Modern intense earthquakes and active volcanic activity (for example, faults of the Kuril-Kamchatka zone) are confined to the zones of their development.

Tectonic movements that cause the formation of folds and ruptures are called mountain-building.

The importance of tectonic conditions for construction. The tectonic features of the area very significantly influence the choice of location of various buildings and structures, their layout, construction conditions and operation of construction projects.

Areas with horizontal, undisturbed layers are favorable for construction. The presence of dislocations and a developed system of tectonic cracks significantly worsens the engineering and geological conditions of the construction area. In particular, during the construction development of a territory with active tectonic activity, it is necessary to take into account the intense fracturing and fragmentation of rocks, which reduces their strength and stability, a sharp increase in seismic activity in places where fault dislocations develop, and other features.

The intensity of oscillatory movements of the earth's crust must be taken into account when constructing protective dams, as well as linear structures of considerable length (canals, railways, etc.).

- these are slow, uneven vertical (lowering or raising) and horizontal tectonic movements of vast areas of the earth's crust, changing the height land and the depths of the seas. They are sometimes also called secular oscillations of the earth's crust.

Causes

The exact reasons for the movements of the earth's crust have not yet been sufficiently elucidated, but one thing is clear that these fluctuations occur under the influence internal forces Earth. The initial cause of all movements of the earth's crust - both horizontal (along the surface) and vertical (mountain building) - is thermal mixing of a substance in the planet's mantle.

On the territory where Moscow is now located, waves splashed in the distant past warm sea. This is evidenced by the thickness of marine sediments with the remains of fish and other animals buried in them, which now lie at a depth of several tens of meters. And at the bottom Mediterranean Sea Not far from the shore, scuba divers found the ruins of an ancient city.

These facts indicate that the earth's crust, which we are accustomed to consider motionless, is experiencing slow uplifts and subsidences. On the Scandinavian Peninsula, you can currently see mountain slopes corroded by the surf at such a high altitude that the waves cannot reach. At the same height, rings are set into the rocks, to which boat chains were once tied. Now from the surface of the water to these rings there are 10 meters, or even more. This means that we can conclude that the Scandinavian Peninsula is currently slowly rising. Scientists have calculated that in some places this rise is occurring at a rate of 1 cm per year. Material from the site

But the western coast of Europe is sinking at about the same speed. To prevent ocean waters from flooding this part of the continent, people built dams along the seashore that stretched for hundreds of kilometers.

Slow movements of the earth's crust occur over the entire surface of the Earth. Moreover, the period of rise is replaced by a period of decline. Once upon a time, the Scandinavian Peninsula was sinking, but in our time it is experiencing an uplift.

Due to movements of the earth's crust, volcanoes are born,

Question 1. What is the earth's crust?

The Earth's crust is the outer hard shell (crust) of the Earth, the upper part of the lithosphere.

Question 2. What types of earth's crust are there?

Continental crust. It consists of several layers. The top is a layer of sedimentary rocks. The thickness of this layer is up to 10-15 km. Beneath it lies a granite layer. The rocks that make it up are similar in their physical properties to granite. The thickness of this layer is from 5 to 15 km. Below the granite layer is a basalt layer consisting of basalt and rocks, physical properties which resemble basalt. The thickness of this layer is from 10 to 35 km.

Oceanic crust. It differs from the continental crust in that it does not have a granite layer or it is very thin, so the thickness of the oceanic crust is only 6-15 km.

Question 3. How do the types of the earth’s crust differ from each other?

Types of the earth's crust differ from each other in thickness. The total thickness of the continental crust reaches 30-70 km. The thickness of the oceanic crust is only 6-15 km.

Question 4. Why do we not notice most of the movements of the earth's crust?

Because the earth's crust moves very slowly, and only friction between plates causes earthquakes.

Question 5. Where and how does the solid shell of the Earth move?

Each point of the earth's crust moves: rises up or falls down, moves forward, backward, right or left relative to other points. Their joint movements lead to the fact that somewhere the earth's crust slowly rises, somewhere it falls.

Question 6. What types of movement are characteristic of the earth's crust?

Slow, or secular, movements of the earth's crust are vertical movements of the Earth's surface at a speed of up to several centimeters per year, associated with the action of processes occurring in its depths.

Earthquakes are associated with ruptures and disturbances in the integrity of rocks in the lithosphere. The zone in which an earthquake originates is called the earthquake source, and the area located on the Earth's surface exactly above the source is called the epicenter. At the epicenter, vibrations of the earth's crust are especially strong.

Question 7. What is the name of the science that studies the movements of the earth's crust?

The science that studies earthquakes is called seismology, from the word “seismos” - vibrations.

Question 8. What is a seismograph?

All earthquakes are clearly recorded by sensitive instruments called seismographs. The seismograph works based on the principle of a pendulum: the sensitive pendulum will definitely respond to any, even the weakest, vibrations of the earth's surface. The pendulum will swing, and this movement will activate the feather, leaving a mark on paper tape. The stronger the earthquake, the more the pendulum oscillates and the more noticeable the mark of the pen on the paper.

Question 9. What is the source of an earthquake?

The zone in which an earthquake originates is called the earthquake source, and the area located on the Earth's surface exactly above the source is called the epicenter.

Question 10. Where is the epicenter of the earthquake?

The area located on the Earth's surface exactly above the source is the epicenter. At the epicenter, vibrations of the earth's crust are especially strong.

Question 11. How do the types of movement of the earth’s crust differ?

Because secular movements of the earth's crust occur very slowly and imperceptibly, and rapid movements of the crust (earthquakes) occur quickly and have destructive consequences.

Question 12. How can secular movements of the earth's crust be detected?

As a result of secular movements of the earth's crust on the Earth's surface, land conditions can be replaced by sea ones - and vice versa. For example, you can find fossilized shells belonging to mollusks on the East European Plain. This suggests that there was once a sea there, but the bottom has risen and now there is a hilly plain.

Question 13. Why do earthquakes occur?

Earthquakes are associated with ruptures and disturbances in the integrity of rocks in the lithosphere. Most earthquakes occur in areas of seismic belts, the largest of which is the Pacific.

Question 14. What is the principle of operation of a seismograph?

The seismograph works on the basis of the pendulum principle: the sensitive pendulum will definitely respond to any, even the weakest, vibrations of the earth's surface. The pendulum will swing, and this movement will activate the pen, leaving a mark on the paper tape. The stronger the earthquake, the greater the swing of the pendulum and the more noticeable the mark of the pen on the paper.

Question 15. What principle is used to determine the strength of an earthquake?

The strength of earthquakes is measured in points. For this purpose, a special 12-point scale of earthquake strength has been developed. The strength of an earthquake is determined by the consequences of this dangerous process, that is, by destruction.

Question 16. Why do volcanoes most often arise at the bottom of the oceans or on their shores?

The emergence of volcanoes is associated with the eruption of material from the mantle to the Earth's surface. Most often this happens where the earth's crust is thin.

Question 17. Using atlas maps, determine where volcanic eruptions occur more often: on land or on the ocean floor?

Most eruptions occur at the bottom and shores of the oceans at the junction of lithospheric plates. For example, along the Pacific coast.