The task of predicting earthquakes based on observations of precursors (predicting not only the location, but, most importantly, the time of a seismic event) is far from being solved, because none of the precursors can be considered reliable. There are isolated cases of exceptionally successful timely forecasts, for example, in 1975 in China an earthquake with a magnitude of 7.3 was very accurately predicted. In earthquake-prone areas, the construction of earthquake-resistant structures plays an important role (see Anti-seismic construction). Dividing the territory according to the degree of potential seismic hazard is part of the task of seismic zoning. It is based on the use of historical data (on the recurrence of seismic events, their strength) and instrumental observations of earthquakes, geological and geographical mapping and information on the movement of the earth’s crust. The zoning of the territory is also associated with the problem of insurance against earthquakes.
Seismograph
Instrumental observations first appeared in China, where in 132 Chang Hen invented a seismoscope, which was a skillfully made vessel. On the outside of the vessel, with a pendulum placed inside, the heads of dragons holding balls in their mouths were engraved in a circle. When the pendulum swung from the earthquake, one or more balls fell into the open mouths of frogs, placed at the base of the vessels so that the frogs could swallow them. A modern seismograph is a set of instruments that record ground vibrations during an earthquake and convert them into an electrical signal, recorded on seismograms in analogue and digital form. However, as before, the main sensitive element is a pendulum with a load.
Seismic service
Constant observations of earthquakes are carried out by the seismic service. The modern global network includes St. 2000 stationary seismic stations, the data of which is systematically published in seismological bulletins and catalogues. In addition to stationary stations, expeditionary seismographs are used, including those installed on the ocean floor. Expedition seismographs were also sent to the Moon (where 5 seismographs annually record up to 3000 moonquakes), as well as to Mars and Venus.
Anthropogenic earthquakes
In con. 20th century Technogenic human activity, which has assumed a planetary scale, has become the cause of induced (artificially caused) seismicity, which occurs, for example, during nuclear explosions (tests at the Nevada test site initiated thousands of seismic tremors), during the construction of reservoirs, the filling of which sometimes provokes strong earthquakes. This happened in India when the construction of the Koyna reservoir caused an 8.0 magnitude earthquake that killed 177 people.
Studying earthquakes
Seismology studies earthquakes. Seismic waves generated during earthquakes are also used to study the internal structure of the Earth; advances in this area served as the basis for the development of seismic exploration methods.
Earthquakes have been observed since ancient times. Detailed historical descriptions that reliably indicate earthquakes since mid. 1 thousand BC, given by the Japanese. Ancient scientists - Aristotle and others - also paid great attention to seismicity. Systematic instrumental observations began in the 2nd half. 19th century, led to the separation of seismology into an independent science (B.B. Golitsyn, E. Wichert, B. Gutenberg, A. Mohorovichic, F. Omori, etc.).
EARTHQUAKE MAGNITUDE (from Latin magnitudo - value), a conventional value characterizing the total energy of elastic vibrations caused by earthquakes or explosions; allows you to compare vibration sources by their energy.
SEISMIC SCALE, a scale for assessing the intensity of an earthquake on the Earth's surface. In the Russian Federation, the 12-point seismic scale MSK-64 is used.
MIDDLE OCEAN RIDGE, mountain structures that form a single system at the bottom of the World Ocean, encircling the entire globe.
LITHOSPHERIC PLATE, a large (several thousand km across) block of the earth’s crust, including not only the continental crust, but also the associated oceanic crust; bounded on all sides by seismically and tectonically active fault zones.
HYPOCENTER, the point at which mass movement begins (rupture rupture) at the source of the earthquake. Depth up to 700 km.
Man-made earthquakes
Recently, information has emerged that earthquakes can be caused by human activity. For example, in areas of flooding during the construction of large reservoirs, tectonic activity increases - the frequency of earthquakes and their magnitude increases. This is due to the fact that the mass of water accumulated in reservoirs, with its weight, increases the pressure in rocks, and seeping water reduces the tensile strength of rocks. Similar phenomena occur when large quantities of rock are removed from mines, quarries, and during the construction of large cities from imported materials.
Earthquake warning
Modern research has shown that by provoking small tremors in the fault zone, it is possible to relieve the pressure that could cause a strong earthquake. Many weak earthquakes, reducing stresses that accumulate over time, can release as much energy as one destructive one.
One way to prevent strong earthquakes is to inject water into wells located along the fault line in which increased pressure has been detected. Water acts like a lubricant, reducing friction between the rocks in the fault and creating the conditions for their smooth movement, accompanied by a series of light tremors.
Another means of generating small earthquakes is explosions along the fault surface.
earthquake earth wobble warning
Earthquake warning using animals
It has long been known that people used more sensitive animals to warn of possible danger. The classic idea is that before earthquakes, some animals sense noise and are able to analyze it. They determine whether they pose a danger or not. If these noises are associated with probable danger, the animals react accordingly. Since not all animals hear danger, but only individual individuals, animals in flocks are saved precisely thanks to individuals.
But the question is, if the science of earthquakes and tsunamis is “extremely simple,” then why the model of the preparation of a tsunami, as a grandiose phenomenon, cannot explain the many associated phenomena. For everyday understanding, the most accessible question is: why, after the “Sumatran disaster” (2004/12/26), among the innumerable victims of our species, not a single corpse of those wild animals that often visit the surf strip, abundant in tasty gifts of the tropical ocean and its seas with bays, was found . What frightened them, surviving only with the help of the maximum performance of their sense organs? The Descartes-Mendeleev-Vernadsky-Larin-ALAN GOA model explains the repelling of animals by the fact that the oversaturation of the source of a giant earthquake with protons was accompanied by pulsed “leaks” of protons, which impulsively migrated most easily along the boundary of the bottom and sea water, that is, within the double electrical layer between solid and liquid phase. The pulses of these protons most intensely jumped into the atmosphere just above the edge of the sea water. Sensitive animals perceived these electrical impulses as unpleasant, and wandered away from the zone of impulse-proton discomfort. Which saved them from the merciless embrace of the tsunami, all of them without exception.
April 26th, 2015Remember, we discussed the article about what, but it also said that “ shale earthquakes are still a poorly understood and difficult to predict phenomenon«
Now the US Geological Survey has presented the first official report on the impact of oil and gas development on seismic activity. Scientists have identified 17 dangerous zones in eight states, and also stated that this kind of man-made earthquakes can reach a magnitude of 7 on the Richter scale - this is enough to collapse buildings. The report is reported by Science News.
Geologists have long known that injecting liquid into underground wells can increase pressure in the pores of deep rocks - this deals the final, decisive blow to faults. However, a sharp increase in the number of small earthquakes in the central United States in recent years has brought particular attention to this phenomenon. The increase in seismic activity coincided with the introduction of new methods of oil and gas extraction.
We are talking mainly about fracking (hydraulic fracturing), where a high-pressure mixture is injected into underground wells, causing gas or oil to flow to the surface. However, the cause of tremors is usually not fracking itself (this operation takes several hours, maximum days), but the injection of waste water into underground horizons, where wider and more dangerous faults are located.
The “red” zones on the map (for example, central Oklahoma) are already approaching the level of seismic danger in states such as California, the epicenter of natural earthquakes in the west of the country. So far, the most destructive man-made earthquake in the United States was a 5.6-magnitude earthquake, the epicenter of which was in the city of Prague in Oklahoma (several dozen houses collapsed at that time).
But geophysicists say the oil and gas industry is capable of more. “There are faults large enough to cause a magnitude seven earthquake. We do not rule out this possibility,” said report co-author Justin Rubinstein.
Seismic hazard maps are typically compiled by the USGS for a 50-year period (also the average "life expectancy" of buildings). However, the intensity of man-made earthquakes depends on rapidly changing factors: wastewater wells are drilled in new areas, falling oil prices force production to stop, state governments change laws governing the oil and gas industry.
For this reason, the new map takes into account the probability of earthquakes within one year. In addition, it will be revised by the end of 2015 - but even now it brings practical benefits: authorities, for example, can decide which bridges in the state to repair first.
Recently, both scientists and officials have begun to take the threat of man-made earthquakes more seriously. Thus, on April 21, 2015, the Oklahoma Geological Survey admitted for the first time that the recent increase in tremors is not due to natural causes, but to the injection of waste water into the formations.
It has long been known that changes in stress in the earth’s crust during large-scale mining of minerals or hydrocarbons automatically entail threats to the movement of layers of the earth’s crust, thereby causing the danger of earthquakes.
One of the first man-made earthquakes associated with oil production occurred in 1939 in the Wilmington field in California. It marked the beginning of a whole cycle of natural disasters that led to the destruction of buildings, roads, bridges, oil wells and pipelines. The problem was solved by pumping water into the oil-bearing formation. But this method is far from a panacea. Water pumped into deep layers can affect the temperature regime of the massif and become one of the causes of an earthquake.
The field stretches through the southwestern areas of Los Angeles and across Long Beach Bay to the coastal areas of the resort city of the same name. The oil and gas bearing area is 54 km 2 . The field was discovered in 1936, and already in 1938 it became the center of California oil production. By 1968, almost 160 million tons of oil and 24 billion m 3 of gas were extracted from the subsoil; in total, they hope to get more than 400 million tons of oil here.
The location of the field in the center of a highly industrialized and densely populated region of southern California, as well as its proximity to the large oil refineries of Los Angeles, was important in the development of the economy of the entire state of California. In this regard, from the beginning of the field's production until 1966, it consistently maintained the highest level of production compared to other oil fields in North America.
In 1939, residents of the cities of Los Angeles and Long Beach felt quite noticeable shaking of the earth's surface - subsidence of the soil above the field began. In the forties, the intensity of this process intensified. An area of sedimentation emerged in the form of an elliptical bowl, the bottom of which fell precisely on the arch of the anticlinal fold, where the level of selection per unit area was maximum. In the 60s, the amplitude of subsidence already reached 8.7 meters. The areas confined to the edges of the subsidence bowl experienced tension. Horizontal displacements with an amplitude of up to 23 cm appeared on the surface, directed towards the center of the area. The movement of soil was accompanied by earthquakes.
Between 1949 and 1961, five fairly strong earthquakes were recorded. The ground was literally disappearing from under our feet. Piers, pipelines, city buildings, highways, bridges and oil wells were destroyed. 150 million US dollars were spent on restoration work. In 1951, the subsidence rate reached a maximum of 81 cm/year. There is a threat of land flooding. Frightened by these events, the city of Long Beach stopped development of the field until the problem was resolved.
By 1954, it was proven that the most effective means of combating subsidence is to inject water into the formation. This also promised an increase in the oil recovery factor. The first stage of waterflooding work began in 1958, when nearly 60 thousand m 3 of water per day began to be pumped into the productive formation on the southern flank of the structure. Ten years later, the injection intensity has already increased to 122 thousand m 3 /day. The subsidence has practically stopped.
Currently, in the center of the bowl it does not exceed 5 cm/year, and in some areas even a surface rise of 15 cm has been recorded. The field has returned to production, with about 1,600 liters of water being injected for every ton of oil withdrawn. Maintaining reservoir pressure currently provides up to 70% of daily oil production in the old areas of Wilmington. In total, the field produces 13,700 tons of oil per day.
Recently, reports have appeared about the subsidence of the North Sea bottom within the Ekofisk field after 172 million tons of oil and 112 billion m 3 of gas were extracted from its depths. It is accompanied by deformations of well bores and offshore oil platforms themselves. The consequences are difficult to predict, but their catastrophic nature is obvious.
Subsidence and earthquakes also occur in the old oil-producing regions of Russia. This is especially strongly felt at the Starogroznenskoye field. Weak earthquakes, as a result of intensive extraction of oil from the subsoil, were felt here in 1971, when an earthquake with an intensity of 7 points occurred at the epicenter, which was located 16 km from the city of Grozny. As a result, residential and administrative buildings were damaged not only in the oil workers' settlement at the field, but also in the city itself. In the old fields of Azerbaijan - Balakhani, Sabunchi, Romany (in the suburbs of Baku) surface subsidence occurs, which leads to horizontal movements. In turn, this causes collapse and breakage of the casing pipes of production oil wells.
Very recent echoes of intensive oil development occurred in Tataria, where in April 1989 an earthquake with a magnitude of up to 6 points was recorded (Mendeleevsk). According to local experts, there is a direct relationship between the increase in oil production from the subsoil and the intensification of small earthquakes. Cases of well bore breakage and column collapse have been recorded. Tremors in this area are especially alarming, because the Tatar Nuclear Power Plant is being built here. In all these cases, one of the effective measures is also the injection of water into the productive formation, compensating for the extraction of oil.
At least 20% of the earthquakes occurring in recent years in the US state of Oklahoma are most likely associated with gas production, which is produced by hydraulic fracturing, according to a study published in the scientific journal Science. Since the beginning of the year, 240 earthquakes of magnitude 3.0 or higher have been recorded in Oklahoma in the south-central United States, twice as many tremors of this magnitude as in California, which is considered the country's "seismic center." Moreover, until 2008, when mass production of gas and oil began in Oklahoma by pumping water into wells, the state experienced no more than one earthquake of this magnitude per year.
Scientists from Cornell University and other organizations concluded in their study that a fifth of all earthquakes in the state are associated with the four largest gas wells southeast of Oklahoma City. According to researchers, activities at these sites can cause tremors within a radius of up to 35 kilometers from their location.
One of the authors of the report, a professor at Columbia University Geoffrey Abers, ruled out the natural origin of the surge in seismic activity in Oklahoma. “Such a large number of repeating earthquakes cannot be part of a natural system,” the British newspaper Guardian quotes the scientist. Local authorities in the United States have previously linked a series of earthquakes with new mining methods that have been actively introduced in the country in recent years. The report, released on Thursday, gives scientific support to these speculations for the first time.
Having begun the exploitation of oil and gas fields, man, without knowing it, let the genie out of the bottle. At first it seemed that oil only brought benefits to people, but it gradually became clear that its use also had a downside. What does oil bring more, benefit or harm? What are the consequences of its use? Won't they turn out to be fatal for humanity?
sources
http://lenta.ru/news/2015/04/24/oilgasearthquakes/
http://www.nefteblog.ru/blog/zemletrjasenie_v_kalifornii_iz_za_dobychi_nefti/2014-06-25-71
http://www.krugosvet.ru/enc/Earth_sciences/geologiya/ZEMLETRYASENIYA.html
http://www.earth-shaking.ru/texnogennye_zemletryaseniya.html
But that's not all there is to worry about in the US, for example, many are waiting. Here’s another famous one, and here’s how it happened in the USA The original article is on the website InfoGlaz.rf Link to the article from which this copy was made -Landslide earthquakes
Earthquakes can also be caused by landslides and large landslides. Such earthquakes are called landslides; they are local in nature and of low strength.
Earthquakes of artificial nature
An earthquake can also be caused artificially: for example, by the explosion of a large amount of explosives or by an underground nuclear explosion (tectonic weapon). Such earthquakes depend on the amount of material exploded. For example, when the DPRK tested a nuclear bomb in 2006, a moderate earthquake occurred, which was recorded in many countries.
Catastrophic earthquakes
Of the huge number of earthquakes that occur annually, only one has a magnitude equal to or greater than 8, ten have a magnitude of 7-7.9, and one hundred have a magnitude of 6-6.9. Any earthquake with a magnitude of St. 7 could be a major disaster. However, it may go unnoticed if it occurs in a desert area. Thus, the enormous natural disaster - the Gobi-Altai earthquake (1957; magnitude 8.5, intensity 11-12 points) - remains almost unstudied, although due to the enormous strength, shallow depth of the source and lack of vegetation cover, this earthquake left surface a complete and diverse picture (2 lakes appeared, a huge thrust was instantly formed in the form of a stone wave up to 10 m high, the maximum displacement along the fault reached 300 m, etc.). An area 50-100 km wide and 500 km long (like Denmark or Holland) was completely destroyed. If this earthquake had occurred in a densely populated area, the death toll could be in the millions. The consequences of one of the most powerful earthquakes (magnitude could be 9), which occurred in the oldest region of Europe - Lisbon - in 1755 and covered an area of over 2.5 million km 2, were so enormous (50 thousand out of 230 thousand citizens died , a rock grew in the harbor, the coastal bottom became dry land, the outline of the coast of Portugal changed) and so amazed the Europeans that Voltaire responded to it with “The Poem on the Death of Lisbon” (1756, Russian translation 1763). Apparently, the impression of this catastrophe was so strong that Voltaire challenged the doctrine of pre-established world harmony in his poem. Strong earthquakes, no matter how rare they are, never leave contemporaries indifferent. Thus, in W. Shakespeare’s tragedy “Romeo and Juliet” (1595), the nurse recalls the earthquake of 1580, which, apparently, the author himself survived.
187 ..14.2. ACTIVATION OF NATURAL PROCESSES DURING UNDERGROUND CONSTRUCTION
Man-made (induced) earthquakes
Man-made (induced) earthquakes most often occur during the creation of large underground reservoirs. The possibility of man-made earthquakes is aggravated by the seismic activity of the underground construction area. About 20% of the territory of the former The USSR was located in a seismically active zone; the area with catastrophic earthquakes of magnitude 9 and above was approximately 300 thousand km2.
An example of increased seismic activity as a result of construction work is the experience of creating a reservoir in the vicinity of Bombay (India). On the river The Koine dam, 103 m high, created a reservoir with a volume of 2.8 km3. It was located in a region composed of traps, broken by faults with a displacement amplitude of several hundred meters. The area was considered seismically inactive. When the reservoir was filled to l/3, weak tremors were recorded (no more than 4 points). The epicenters of the earthquakes were located under the dam and 40 km from it. When the reservoir was filled to a height of 100 m, a strong earthquake with a magnitude of 6.4 occurred, causing severe destruction in Koynagar, located 1.5 km from the dam (Fig. 14.5).
During the construction and operation of hydraulic structures, the following features of man-made earthquakes can be observed:
1) there is an ambiguous connection between the creation of reservoirs and seismic activity: there are known cases of a decrease in seismic activity near the reservoir;
2) man-made earthquakes are localized within a radius of 30 km from the site of large hydraulic structures;
3) there is a connection between seismic activity and changes in the level of the reservoir, and the manifestations of seismicity lag in time by one to two months;
4) activation of earthquakes occurs in cases when the level of the reservoir exceeds 90-100 m with its volume exceeding 10 billion m3.
The strength of man-made earthquakes can vary from small ground vibrations caused by the movement of cars and trains, to noticeable shaking during volleys, explosions, underground nuclear tests, etc.
Man-made earthquakes can be caused by underground waste disposal. Thus, the injection of water contaminated with radioactive waste into deep wells drilled for this purpose in the 70s near the Rocky Mount military plant (Colorado, near Denver, USA) caused more than 700 small earthquakes around the wells. The increased fluid pressure at the bottom of the wells facilitated movement along cracks in local, highly fractured rocks; the frequency of earthquakes corresponded to the volume and pressure of injected water. Stopping water injection led to the cessation of oscillations. This experience in Colorado suggested that artificially induced earthquakes could weaken elastic deformations along active faults, promoting the development of displacements along them, and thereby reduce the risk of a powerful shock.
Man-made earthquakes are also observed in areas of recent continental glaciation, which is due to the removal of the load of the ice sheet and leads to a vertical rise in the areas of mining.
The causes of man-made earthquakes in underground construction are the special nature of the change in the stress-strain state of the rock mass as a result of mining construction activities, in which existing tectonic faults are activated or new faults or zones of deep fractures with a certain inclined surface appear. In this case, disturbed rocks undergo shape distortion and a decrease in volume at depth under the influence of pressure, which in turn causes phase changes in minerals from less dense to more dense, despite their heating. Blocks of rocks lying on opposite sides of the rupture, being in close contact, are capable of accumulating elastic deformation, gradually changing their shape until their elastic limit is reached. After
This causes a sharp cleavage, and a significant part of the accumulated elastic energy is released in the form of seismic waves. The rock blocks return to their original shape, but find themselves disturbed and displaced relative to each other on opposite sides of the resulting gap (Fig. 14.6).
Rice. 14.5. Koyna earthquake diagram:
I - reservoir; 2 - Koyna dam; 3 - epicenter (8-9 points); 4 - nzoseists
Another cause of man-made earthquakes may be a disruption of heat transfer processes as a result of undermining of the rock mass. The appearance of heterogeneous thermal zones in combination with high pressure causes a direct change in the volume of rocks. A change in volume - be it expansion or compression - leads to movement, which can be accompanied by the formation of ruptures.
A change in the nature of mass transfer processes can also be the cause of a man-made earthquake. It is known that the strength of rocks can sharply decrease upon contact with certain liquids or gases. Moderate mineralization of groundwater increases the reduction in rock strength, especially if the solution contains the same ions as the rock. Water confined in fractured rocks or in crushing zones experiences elastic compression, which extends to a depth of several kilometers and is measured in several tens of millimeters. To transfer pressure over 1 km, a time of several days is required; surface pore pressure is transmitted to a depth of 10 km within 100 days. Outside the zone of fractured rocks, pressure transfer is even slower. Due to the time difference between the increase in pore pressure in the zone of intense fracturing and in the non-fractured part of the rock mass, a decrease in resistance in the zone of intense fracturing or crushing may occur. The consequence of this may be a release of stress, expressed on the surface in the form of an earthquake. Consequently, in a more general form, the causes of man-made earthquakes can be characterized as follows:
1) the location of the mining construction site to tectonically active and discontinuous structures of the region;
2) the presence of temperature anomalies (geothermal gradient, thermal waters, etc.);
3) the presence of a hydraulic connection between surface and groundwater and activation of mass transfer processes.
All the described processes - landslides, rock collapse, karst formation, man-made earthquakes - are the results of the complex structure of the rock mass and the stress-strain state of the massif, which quickly loses its stability under any engineering influence on it. Underground construction, which is characterized, as a rule, by the presence of weak, water-logged host rocks, is associated with the activation of all negative natural processes of natural redistribution of stresses in the massif. Therefore, the environmental hazard of underground construction processes can only be considered with an integrated approach to studying the patterns of mutual influence of underground objects and the environment.
In this article you will learn what is an earthquake, for what reasons does it occur and how dangerous it can be for humans. Also learn about the types of earthquakes and how to measure force.
Earthquakes are one of the most serious enemies for humans, due to their nature of origin and destructive potential. Depending on the strength of the tremors, destruction on the surface of the earth can reach catastrophic proportions. No matter how strong buildings and any human structures are, everything can be destroyed by the force of nature.
About a million earthquakes occur on our planet every year, most of which do not cause harm to humans and are not even physically felt. But strong tremors occur periodically (approximately once every two weeks), posing a threat to human life. Most earthquakes occur on the ocean floor, which is the cause of another natural phenomenon - tsunami, which can be no less dangerous, destroying everything in its path with a tidal wave. The danger of a tsunami occurs only in coastal areas and with a significant earthquake, and earthquakes are dangerous for almost the entire planet.
An earthquake is nothing more than tremors, provoked by processes occurring inside our planet, is a seismic phenomenon that occurs as a result of sharp displacements of the earth's crust. This process can occur at great depths in the bowels of the earth, but most often on the surface (up to 100 km).
Earthquakes are the final stage of the movement of Earth's rocks. The friction force prevents shifts in the earth's crust, but when the stress reaches a critical level, a sharp displacement occurs with rock rupture, the energy of the friction force finds an outlet in motion, the vibrations from which spread, like sound waves, in all directions. The place where the fault or movement occurs is called the focus of the earthquake, A a point on the earth's surface above the focus - the epicenter of the earthquake. As you move away from the epicenter, the strength of the shock wave decreases. The speed of such waves can reach 7-8 km per second.
The causes of earthquakes are tectonic processes(associated with natural movement or deformation of the earth's crust or mantle), volcanic and other less serious ones associated with collapses, landslides, filling of reservoirs, collapse of underground mine cavities, explosions and other changes, most often provoked by human activity, which are called artificial pathogens.
Types of earthquakes
Volcanic earthquakes arise as a result of high tension in the depths of the volcano, due to the movements of lava or volcanic gas. Such earthquakes do not pose a great threat to humans, but they continue for a long time and repeatedly.
Man-made earthquakes caused by human activity, for example, in the event of flooding during the construction of large reservoirs, during the extraction of oil or natural gas, coal, that is, when the integrity of the earth’s crust is violated. Earthquakes in such cases do not have large magnitudes, but can be dangerous for a small area of the Earth’s surface, and also provoke more serious tectonic changes, which entails an increase in the stress of rocks in the planet’s crust.
Landslide earthquakes caused by landslides and large landslides, are not so dangerous and are local in nature.
Man-made earthquakes arise in the case of the use of powerful weapons or the use of climate weapons (tectonic weapons). The strength of such earthquakes depends on the power of the explosion or the intensity of use (in the case of climate weapons). Information about the use of tectonic weapons is most often classified for mere mortals, and one can only guess what exactly led to an earthquake in a particular region of the planet.
To measure the strength of an earthquake, a magnitude scale and an intensity scale are used..
Magnitude scale– a relative characteristic of an earthquake, which has its own varieties: local magnitude (ML), surface wave magnitude (MS), body wave magnitude (MB), moment magnitude (MW). The most popular scale is the local magnitude scale of Richter, who in 1935 proposed this method of measuring the strength of earthquakes, which gave the name to this scale. The Richter scale has a range from 1 to 9, the magnitude of the magnitude is measured by a special device - a seismograph. The magnitude scale is often confused with the 12-point scale, which evaluates the external manifestations of tremors (destruction, impact on people, natural objects). At the moment of the shock itself, first of all, data is received on the magnitude of the magnitude, and after the earthquake - the strength of the earthquake, which is measured on an intensity scale.
Intensity scale– a qualitative characteristic of an earthquake, indicating the nature and scale of this phenomenon in relation to humans, animals, nature, natural and artificial structures in the earthquake affected area.
The intensity of an earthquake can be determined in terms of one of the accepted seismological intensity scales, or by the maximum kinematic parameters of vibrations of the earth's surface
Different countries have different ways of measuring the intensity of an earthquake.:
In Russia and some other countries, the 12-point Medvedev-Sponheuer-Karnik scale has been adopted.
In Europe - 12-point European macroseismic scale.
In the USA - a 12-point modified Mercalli scale.
In Japan - 7-point scale of the Japan Meteorological Agency.
Let's see what these numbers mean, excluding the Japanese method of measurement:
3 points - minor vibrations that are noticed by particularly sensitive people who are indoors at the time of the earthquake.
5 points - there is swaying of objects in the room, shocks are felt by everyone who is conscious.
6-7 points - destruction of buildings, cracks in the earth’s crust are possible, tremors are felt in any area and in any room.
8-10 points - buildings of almost any design begin to collapse, it is difficult for a person to stand on his feet, and large cracks may appear in the earth’s crust.
Reasoning logically, one can roughly imagine that a smaller value on this scale causes less damage, while a maximum value wipes everything off the face of the Earth.