What does it mean to predict an earthquake? Modern methods of earthquake prediction

Is it possible to predict an earthquake? Over the past centuries, many methods of prediction have been proposed - from taking into account weather conditions typical of earthquakes, to observing the position of celestial bodies and oddities in the behavior of animals. Most attempts to predict earthquakes have been unsuccessful.

Since the early 1960s, scientific research on earthquake forecasting has taken on an unprecedented scale, especially in Japan, the USSR, China and the USA. Their goal is to make earthquake prediction at least as reliable as weather forecasting. The most famous is the prediction of the time and place of occurrence of a destructive earthquake, especially short-term forecast. However, there is another type of earthquake forecast: an assessment of the intensity of seismic shaking expected in each individual area. This factor plays a major role in the selection of sites for the construction of important structures such as dams, hospitals, nuclear reactors, and is ultimately most important in reducing seismic hazards.

Studying the nature of seismicity on Earth over a historical period of time has made it possible to predict those places where destructive earthquakes may occur in the future. However, the chronicle of past earthquakes does not make it possible to predict the exact time of the next catastrophe. Even in China, where between 500 and 1,000 devastating earthquakes have occurred over the past 2,700 years, statistical analysis has not revealed a clear periodicity of the largest earthquakes, but has shown that major catastrophes can be separated by long periods of seismic silence.

In Japan, which also has a long history of earthquakes, intensive research on earthquake forecasting has been carried out since 1962, but so far it has not brought any success. The Japanese program, combining the efforts of hundreds of seismologists, geophysicists and surveyors, led to the receipt of a huge amount of diverse information and made it possible to identify many signs of an impending earthquake. One of the most remarkable earthquake precursors among those studied so far is the phenomena noted on the west coast of the Japanese island of Honshu. Geodetic measurements carried out there showed that in the vicinity of the city of Niigata there was a continuous rise and fall of the coastline for about 60 years. In the late 1950s, the rate of this process decreased; then during an earthquake. Niigata On June 16, 1964, in the northern part of this area (near the epicenter), a sharp subsidence of more than 20 cm was noted. The nature of the distribution of vertical movements shown in the graphs was clarified only after the earthquake. But should such major changes in elevation occur again, this will undoubtedly serve as some caution. Later in Japan, a special study of historical earthquake cycles in the vicinity of Tokyo was carried out, and local measurements of modern crustal deformation and earthquake frequency were also carried out. The results have led some Japanese seismologists to suggest that a repeat of the great Kanto earthquake (1923) is not currently expected, but that earthquakes cannot be ruled out in neighboring areas.

Since the beginning of this century, if not earlier, assumptions have been made about different types of “trigger mechanisms” capable of causing the initial movement of the earthquake source. Among the most serious assumptions are the role of harsh weather conditions, volcanic eruptions, and the gravitational pull of the Moon, Sun and planets. Numerous earthquake catalogs, including very comprehensive lists for California, have been analyzed to find such effects, but no definitive results have been obtained. For example, it has been suggested that since every 179 years the planets find themselves approximately in one line, the resulting additional attraction causes a sharp increase in seismicity. The San Andreas Fault in southern California has not produced destructive seismic shocks since the Fort Tejon earthquake in 1857, so the impact of this "planetary" trigger on the said fault in 1982 would be considered especially likely. Fortunately for California, this argument is seriously flawed. Firstly, world earthquake catalogs show that in past episodes of such an arrangement of planets: in 1803, 1624 and 1445, no increase in seismic activity was observed. Second, the additional attraction of relatively small or distant planets is negligible compared to the interaction between the Earth and the Sun. This means that in addition to the 179-year period, we must also consider the possibility of many other periodicities associated with the joint action of the largest celestial bodies.

To provide a reliable forecast, such as predicting the phases of the moon or the outcome of a chemical reaction, a strong theoretical basis is usually necessary. Unfortunately, at present there is still no precisely formulated theory of the origin of earthquakes. However, based on our current, albeit limited, knowledge of where and when seismic tremors occur, we can make rough predictions about when the next largest earthquake can be expected on any known fault. Indeed, after the 1906 earthquake, G. F. Reed, using the theory of elastic recoil, stated that the next major earthquake in the San Francisco area would occur in about a hundred years.

Currently, a lot of experimental work is being carried out. Various phenomena are being studied that may turn out to be harbingers, “symptoms” of an impending earthquake. Although attempts at a comprehensive solution to the problem look quite impressive, they provide little reason for optimism: the forecast system is unlikely to be practically implemented in most parts of the world in the near future. In addition, the methods that now seem to be the most promising require very complex equipment and a lot of effort from scientists. Establishing networks of forecasting stations in all high seismic risk areas would be extremely expensive.

In addition, one major dilemma is inextricably linked with earthquake forecasting. Suppose seismological measurement data indicates that an earthquake of a certain magnitude will occur in a certain area within a certain period of time. It must be assumed that this area was previously considered seismic, otherwise such studies would not have been carried out on it. It follows that if an earthquake actually occurs during the specified period, it may turn out to be a mere coincidence and will not be strong evidence that the methods used for the forecast are correct and will not lead to errors in the future. And of course, if you make a specific prediction and nothing happens, this will be taken as evidence that the method is unreliable.

Recently, there has been a significant increase in earthquake forecasting activity in California; As a result, in 1975, a scientific council was formed whose task is to evaluate the reliability of forecasts for the state emergency response agency.

It was decided that every forecast to be considered should include four main elements: 1) the time during which the event will occur, 2) the location at which it will occur, 3) the magnitude limits, 4) an estimate of the probability of a random coincidence, i.e. that an earthquake will occur without connection with phenomena that have been subjected to special study.

The significance of such a council is not only that it carries out the task of the authorities responsible for ensuring minimal losses during an earthquake, but also that the caution exercised by such a council is useful to scientists making forecasts, since it provides independent verification. On a broader social scale, such a scientific jury helps to weed out the unfounded predictions of all sorts of clairvoyants and sometimes unscrupulous people seeking fame.

The social and economic consequences of earthquake forecasting are subject to conflicting interpretations. As seismological research progresses in various countries, numerous predictions are likely to be made about earthquakes that are expected to occur in likely source zones.

In Western countries, negative as well as positive consequences of the prognosis have been studied. If, for example, in some place it was possible to confidently predict the time of a major destructive earthquake about a year before the expected date and then continuously refine it, then the number of victims and even the amount of material damage from this earthquake would be significantly reduced, but public relations in the area would be disrupted and the local economy would collapse.

The only example of a successfully predicted earthquake to date is the 1975 Haicheng earthquake in Liaoning Province in China. In those years, long before the earthquake, a network of geological, geophysical and other observations was organized in China to monitor changes in the physical state of the earth's interior, surface slopes, seismic activity, groundwater levels and the content of various gases in them. Based on all the data received, a decision was made to evacuate the city's population. A few hours later he found himself under the ruins, but there were almost no casualties.

Returning to the extremely complex task of predicting earthquakes, we note that scientists in many countries continue to search for earthquake harbingers. Today they are divided into several groups.

First of all, these are seismological precursors - an increase in the number of foreshocks of a large earthquake.

Geophysical signs include a decrease in the electrical resistance of rocks, fluctuations in the modulus of the total magnetic field vector, etc.

Among the hydrogeological precursors of an earthquake are a decrease, and then a sharp increase in the level of groundwater in wells and wells, a change in water temperature, an increased content of radon, carbon dioxide and mercury vapor.

And, of course, abnormal animal behavior

Not a year goes by without a catastrophic earthquake happening somewhere, causing total destruction and casualties, the number of which can reach tens and hundreds of thousands. And then there is the tsunami - abnormally high waves that arise in the oceans after earthquakes and wash away villages and cities along with their inhabitants on the low shores. These disasters are always unexpected; their suddenness and unpredictability are frightening. Is modern science really unable to foresee such cataclysms? After all, they predict hurricanes, tornadoes, weather changes, floods, magnetic storms, even volcanic eruptions, but with earthquakes - complete failure. And society often believes that scientists are to blame. Thus, in Italy, six geophysicists and seismologists were put on trial for failing to predict the earthquake in L'Aquila in 2009, which claimed the lives of 300 people.

It would seem that there are many different instrumental methods and instruments that record the slightest deformations of the earth’s crust. But the earthquake forecast fails. So what's the deal? To answer this question, let's first consider what an earthquake is.

The uppermost shell of the Earth - the lithosphere, consisting of a solid crust with a thickness of 5–10 km in the oceans and up to 70 km under mountain ranges - is divided into a number of plates called lithospheric. Below is also the solid upper mantle, or more precisely, its upper part. These geospheres consist of various rocks that have high hardness. But in the thickness of the upper mantle at different depths there is a layer called asthenospheric (from the Greek asthenos - weak), which has a lower viscosity compared to the above and underlying mantle rocks. It is assumed that the asthenosphere is the “lubricant” through which lithospheric plates and parts of the upper mantle can move.

During movement, the plates collide in some places, forming huge folded mountain chains, in others, on the contrary, they split to form oceans, the crust of which is heavier than the crust of the continents and is capable of sinking under them. These plate interactions cause enormous stress in rocks, compressing or, conversely, stretching them. When stresses exceed the tensile strength of rocks, they undergo very rapid, almost instantaneous displacement and rupture. The moment of this displacement constitutes an earthquake. If we want to predict it, we must give a forecast of place, time and possible strength.

Any earthquake is a process that occurs at a certain finite speed, with the formation and renewal of many different-scale ruptures, the ripping up of each of them with the release and redistribution of energy. At the same time, it is necessary to clearly understand that rocks are not a continuous homogeneous massif. It has cracks, structurally weakened zones, which significantly reduce its overall strength.

The speed of propagation of a rupture or ruptures reaches several kilometers per second, the destruction process covers a certain volume of rocks - the source of the earthquake. Its center is called the hypocenter, and its projection onto the Earth's surface is called the epicenter of the earthquake. Hypocenters are located at different depths. The deepest ones are up to 700 km, but often much less.

The intensity, or strength, of earthquakes, which is so important for forecasting, is characterized in points (a measure of destruction) on the MSK-64 scale: from 1 to 12, as well as by magnitude M, a dimensionless value proposed by Caltech professor C. F. Richter, which reflects the amount of released total energy of elastic vibrations.

What is a forecast?

To assess the possibility and practical usefulness of earthquake forecasting, it is necessary to clearly define what requirements it must meet. This is not guessing, not a trivial prediction of obviously regular events. A forecast is defined as a scientifically based judgment about the place, time and state of a phenomenon, the patterns of occurrence, spread and change of which are unknown or unclear.

The fundamental predictability of seismic disasters has not raised any doubts for many years. Belief in the limitless predictive potential of science was supported by seemingly quite convincing arguments. Seismic events with the release of enormous energy cannot occur in the bowels of the Earth without preparation. It should include certain restructuring of the structure and geophysical fields, the greater the more intense the expected earthquake. Manifestations of such restructuring - anomalous changes in certain parameters of the geological environment - are detected by methods of geological, geophysical and geodetic monitoring. The task, therefore, was to, having the necessary techniques and equipment, timely record the occurrence and development of such anomalies.

However, it turned out that even in areas where continuous careful observations are carried out - in California (USA), Japan - the strongest earthquakes happen unexpectedly every time. It is not possible to obtain a reliable and accurate forecast empirically. The reason for this was seen in insufficient knowledge of the mechanism of the process under study.

Thus, the seismic process was considered a priori to be predictable in principle if the mechanisms, evidence and necessary techniques, unclear or insufficient today, are understood, supplemented and improved in the future. There are no fundamentally insurmountable obstacles to forecasting. The postulates of the limitless possibilities of scientific knowledge, inherited from classical science, and the prediction of processes that interest us were, until relatively recently, the initial principles of any natural scientific research. How is this problem understood now?

It is quite obvious that even without special research it is possible to confidently “predict”, for example, a strong earthquake in the highly seismic zone of transition from the Asian continent to the Pacific Ocean in the next 1000 years. It can be just as “reasonably” stated that in the area of Iturup Island in the Kuril Ridge tomorrow at 14:00 Moscow time there will be an earthquake with a magnitude of 5.5. But the price for such forecasts is a pittance. The first of the forecasts is quite reliable, but no one needs it due to its extremely low accuracy; the second is quite accurate, but also useless, because its reliability is close to zero.

From this it is clear that: a) at any given level of knowledge, an increase in the reliability of the forecast entails a decrease in its accuracy, and vice versa; b) if the forecast accuracy of any two parameters (for example, the location and magnitude of an earthquake) is insufficient, even an accurate prediction of the third parameter (time) loses practical meaning.

Thus, the main task and main difficulty of predicting an earthquake is that predictions of its location, time and energy or intensity would satisfy the practical requirements at the same time in terms of accuracy and reliability. However, these requirements themselves vary depending not only on the achieved level of knowledge about earthquakes, but also on the specific forecasting goals that are met by different types of forecast. It is customary to highlight:

seismic zoning (seismicity estimates for decades - centuries);
forecasts: long-term (for years - decades), medium-term (for months - years), short-term (in time 2-3 days - hours, in place 30-50 km) and sometimes operational (in hours - minutes).

The short-term forecast is especially relevant: it is this that is the basis for specific warnings about the upcoming disaster and for urgent actions to reduce the damage from it. The cost of mistakes here is very high. These errors are of two types:

A “false alarm” is when, after taking all measures to minimize the number of casualties and material losses, the predicted strong earthquake does not occur.
“Missing the target” when the earthquake that took place was not predicted. Such errors are extremely common: almost all catastrophic earthquakes are unexpected.

In the first case, the damage from disrupting the rhythm of life and work of thousands of people can be very large; in the second, the consequences are fraught not only with material losses, but also with human casualties. In both cases, the moral responsibility of seismologists for an incorrect forecast is very high. This forces them to be extremely careful when issuing (or not issuing) official warnings to the authorities about the impending danger. In turn, the authorities, realizing the enormous difficulties and dire consequences of stopping the functioning of a densely populated area or large city for at least a day or two, are in no hurry to follow the recommendations of numerous “amateur” unofficial forecasters who declare 90% and even 100% reliability your predictions.

The high price of ignorance

Meanwhile, the unpredictability of geocatastrophes is very costly for humanity. As Russian seismologist A.D. Zavyalov notes, for example, from 1965 to 1999 earthquakes accounted for 13% of the total number of natural disasters in the world. From 1900 to 1999, there were 2,000 earthquakes with a magnitude greater than 7. In 65 of them, M was greater than 8. Human losses from earthquakes in the 20th century amounted to 1.4 million people. Of these, in the last 30 years, when the number of victims began to be calculated more accurately, there were 987 thousand people, that is, 32.9 thousand people per year. Among all natural disasters, earthquakes rank third in terms of the number of deaths (17% of the total number of deaths). In Russia, on 25% of its area, where about 3,000 cities and towns, 100 large hydro and thermal power plants, and five nuclear power plants are located, seismic shocks with an intensity of 7 or more are possible. The strongest earthquakes in the twentieth century occurred in Kamchatka (November 4, 1952, M = 9.0), in the Aleutian Islands (March 9, 1957, M = 9.1), in Chile (May 22, 1960, M = 9.5 ), in Alaska (March 28, 1964, M = 9.2).

The list of the strongest earthquakes in recent years is impressive.

2004, December 26. Sumatra-Andaman earthquake, M = 9.3. The strongest aftershock (repeated shock) with M = 7.5 occurred 3 hours 22 minutes after the main shock. In the first 24 hours after it, about 220 new earthquakes with M > 4.6 were registered. The tsunami hit the coasts of Sri Lanka, India, Indonesia, Thailand, Malaysia; 230 thousand people died. Three months later, an aftershock with M = 8.6 occurred.

2005, March 28. Nias Island, three kilometers from Sumatra, earthquake with M = 8.2. 1300 people died.

2005, October 8. Pakistan, earthquake with M = 7.6; 73 thousand people died, more than three million were left homeless.

2006, May 27. Java Island, earthquake with M = 6.2; 6,618 people died, 647 thousand were left homeless.

2008, May 12. Sichuan Province, China, 92 km from Chengdu, earthquake M = 7.9; 87 thousand people were killed, 370 thousand were injured, 5 million were left homeless.

2009, April 6. Italy, earthquake with M = 5.8 near the historical city of L'Aquila; 300 people became victims, 1.5 thousand were injured, more than 50 thousand were left homeless.

2010, January 12. The island of Haiti, a few miles off the coast, two earthquakes with M = 7.0 and 5.9 within a few minutes. About 220 thousand people died.

2011, March 11. Japan, two earthquakes: M = 9.0, epicenter 373 km northeast of Tokyo; M = 7.1, epicenter 505 km northeast of Tokyo. Catastrophic tsunami, more than 13 thousand people died, 15.5 thousand went missing, destruction of the nuclear power plant. 30 minutes after the main shock - an aftershock with M = 7.9, then another shock with M = 7.7. During the first day after the earthquake, about 160 shocks with magnitudes from 4.6 to 7.1 were registered, of which 22 shocks with M > 6. During the second day, the number of registered aftershocks with M > 4.6 was about 130 (of which 7 aftershocks with M > 6.0). During the third day, this number dropped to 86 (including one shock with M = 6.0). On the 28th day, an earthquake with M = 7.1 occurred. By April 12, 940 aftershocks with M > 4.6 were recorded. The epicenters of the aftershocks covered an area about 650 km long and about 350 km across.

All, without exception, of the listed events turned out to be unexpected or “predicted” not so definitely and accurately that specific safety measures could be taken. Meanwhile, statements about the possibility and even repeated implementation of a reliable short-term forecast of specific earthquakes are not uncommon both on the pages of scientific publications and on the Internet.

A Tale of Two Forecasts

In the area of the city of Haicheng, Liaoning Province (China), in the early 70s of the last century, signs of a possible strong earthquake were repeatedly noted: changes in the slopes of the earth's surface, geomagnetic field, soil electrical resistance, water level in wells, and animal behavior. In January 1975, the impending danger was announced. By the beginning of February, the water level in the wells suddenly rose, and the number of weak earthquakes increased greatly. By the evening of February 3, the authorities were notified by seismologists of an imminent disaster. The next morning there was an earthquake with a magnitude of 4.7. At 14:00 it was announced that an even stronger impact was likely. Residents left their homes and security measures were taken. At 19:36, a powerful shock (M = 7.3) caused widespread destruction, but there were few casualties.

This is the only example of a surprisingly accurate short-term forecast of a devastating earthquake in time, location and (approximately) intensity. However, other, very few forecasts that came true were insufficiently definite. The main thing is that the number of both unpredicted real events and false alarms remained extremely large. This meant that there was no reliable algorithm for stable and accurate prediction of seismic disasters, and the Haicheng forecast was most likely just an unusually successful coincidence of circumstances. So, a little more than a year later, in July 1976, an earthquake with M = 7.9 occurred 200–300 km east of Beijing. The city of Tangshan was completely destroyed, killing 250 thousand people. There were no specific harbingers of the disaster, and no alarm was declared.

After this, and also after the failure of a long-term experiment to predict the earthquake in Parkfield (USA, California) in the mid-80s of the last century, skepticism prevailed about the prospects for solving the problem. This was reflected in most of the reports at the meeting “Evaluation of Earthquake Forecast Projects” in London (1996), held by the Royal Astronomical Society and the Joint Association of Geophysics, as well as in the discussion of seismologists from different countries on the pages of the journal "Nature"(February - April 1999).

Much later than the Tangshan earthquake, the Russian scientist A. A. Lyubushin, analyzing geophysical monitoring data of those years, was able to identify an anomaly that preceded this event (in the upper graph of Fig. 1 it is highlighted by the right vertical line). The anomaly corresponding to this catastrophe is also present in the lower, modified graph of the signal. Both graphs contain other anomalies that are not much worse than the one mentioned, but do not coincide with any earthquakes. But no precursor to the Haicheng earthquake (left vertical line) was initially found; the anomaly was revealed only after modifying the graph (Fig. 1, bottom). Thus, although it was possible to identify the precursors of the Tangshan and, to a lesser extent, Haicheng earthquakes a posteriori in this case, a reliable predictive identification of signs of future destructive events was not found.

Nowadays, analyzing the results of long-term, since 1997, continuous recordings of the microseismic background on the Japanese Islands, A. Lyubushin discovered that even six months before the strong earthquake on the island. Hokkaido (M = 8.3; September 25, 2003) there was a decrease in the time-average value of the precursor signal, after which the signal did not return to its previous level and stabilized at low values. Since mid-2002, this has been accompanied by an increase in the synchronization of the values of this characteristic across different stations. From the standpoint of catastrophe theory, such synchronization is a sign of the approaching transition of the system under study to a qualitatively new state, in this case an indication of an impending disaster. These and subsequent results of processing the available data led to the assumption that the event on the island. Hokkaido, although strong, is just a foreshock of an even more powerful upcoming catastrophe. So, in Fig. Figure 2 shows two anomalies in the behavior of the precursor signal - sharp minima in 2002 and 2009. Since the first of them was followed by an earthquake on September 25, 2003, the second minimum could be a harbinger of an even more powerful event with M = 8.5–9. Its place was indicated as “Japanese Islands”; it was more accurately determined retrospectively, after the fact. The time of the event was first predicted (April 2010) for July 2010, then from July 2010 for an indefinite period, which excluded the possibility of declaring an alarm. It happened on March 11, 2011, and, judging by Fig. 2, it could have been expected earlier and later.

This forecast refers to the medium-term ones, which have been successful before. Short-term successful forecasts are always rare: it was not possible to find any consistently effective set of precursors. And now there is no way to know in advance in what situations the same precursors will be effective as in A. Lyubushin’s forecast.

Lessons from the past, doubts and hopes for the future

What is the current state of the problem of short-term seismic forecasting? The range of opinions is very wide.

In the last 50 years, attempts to predict the location and time of strong earthquakes within a few days have been unsuccessful. It was not possible to identify the precursors of specific earthquakes. Local disturbances of various environmental parameters cannot be precursors of individual earthquakes. It is possible that a short-term forecast with the required accuracy is generally unrealistic.

In September 2012, during the 33rd General Assembly of the European Seismological Commission (Moscow), the Secretary General of the International Association of Seismology and Physics of the Earth's Interior P. Sukhadolk admitted that breakthrough solutions in seismology are not expected in the near future. It was noted that none of the more than 600 known precursors and no set of them guarantee the prediction of earthquakes, which occur without precursors. It is not possible to confidently indicate the place, time, and power of the cataclysm. Hopes are pinned only on predictions where strong earthquakes occur with some frequency.

So is it possible in the future to increase both the accuracy and reliability of the forecast? Before looking for the answer, you should understand: why, in fact, should earthquakes be predictable? It is traditionally believed that any phenomenon is predictable if similar events that have already occurred are studied sufficiently fully, in detail and accurately, and forecasting can be built by analogy. But future events occur under conditions that are not identical to the previous ones, and therefore will certainly differ from them in some way. This approach can be effective if, as is implied, the differences in the conditions of the origin and development of the process under study in different places at different times are small and change its result in proportion to the magnitude of such differences, that is, also insignificantly. When such deviations are repeated, random, and have different meanings, they significantly cancel each other out, making it possible to ultimately obtain a not absolutely accurate, but statistically acceptable forecast. However, the possibility of such predictability was called into question at the end of the 20th century.

Pendulum and sand pile

It is known that the behavior of many natural systems is described quite satisfactorily by nonlinear differential equations. But their decisions at a certain critical point in evolution become unstable and ambiguous - the theoretical trajectory of development branches out. One or another of the branches is unpredictably realized under the influence of one of the many small random fluctuations that always occur in any system. It would be possible to predict the choice only with precise knowledge of the initial conditions. But nonlinear systems are very sensitive to their slightest changes. Because of this, choosing a path sequentially at only two or three branching points (bifurcations) leads to the fact that the behavior of solutions to completely deterministic equations turns out to be chaotic. This is expressed - even with a gradual increase in the values of any parameter, for example pressure - in the self-organization of collective irregular, abruptly rearranging movements and deformations of system elements and their aggregations. Such a regime, paradoxically combining determinism and chaos and defined as deterministic chaos, different from complete disorder, is by no means exceptional, and not only in nature. Let's give the simplest examples.

By squeezing a flexible ruler strictly along the longitudinal axis, we will not be able to predict in which direction it will bend. Swinging a frictionless pendulum so much that it reaches the point of the upper, unstable equilibrium position, but no more, we cannot predict whether the pendulum will go backwards or make a full revolution. By sending one billiard ball in the direction of another, we approximately predict the trajectory of the latter, but after its collisions with the third, and even more so with the fourth ball, our predictions will turn out to be very inaccurate and unstable. By increasing a pile of sand with a uniform addition, when a certain critical angle of its slope is reached, we will see, along with the rolling of individual grains of sand, unpredictable avalanche-like collapses of spontaneously arising aggregations of grains. This is the deterministic-chaotic behavior of a system in a state of self-organized criticality. The patterns of mechanical behavior of individual sand grains are supplemented here with qualitatively new features determined by the internal connections of the aggregate of sand grains as a system.

In a fundamentally similar way, the discontinuous structure of rock masses is formed - from the initial dispersed microcracking to the growth of individual cracks, then to their interactions and interconnections. The rapid growth of a single, previously unpredictable disturbance among competing ones turns it into a major seismogenic rupture. In this process, each single act of rupture formation causes unpredictable rearrangements of the structure and stress state in the massif.

In the above and other similar examples, neither the final nor intermediate results of the nonlinear evolution determined by the initial conditions are predicted. This is not due to the influence of many factors that are difficult to take into account, not to ignorance of the laws of mechanical motion, but to the inability to estimate the initial conditions absolutely accurately. In these circumstances, even the slightest differences quickly push initially similar developmental trajectories as far apart as desired.

The traditional strategy for predicting disasters comes down to identifying a distinct precursor anomaly, generated, for example, by the concentration of stresses at the ends, kinks, and intersections of discontinuities. To become a reliable sign of an approaching shock, such an anomaly must be single and stand out in contrast against the surrounding background. But the real geoenvironment is structured differently. Under load, it behaves as a rough and self-similar block (fractal). This means that a block of any scale level contains relatively few blocks of smaller sizes, and each of them contains the same number of even smaller ones, etc. In such a structure there cannot be clearly isolated anomalies on a homogeneous background; it contains non-contrasting macro-, meso- and microanomalies.

This makes traditional tactics for solving the problem futile. Monitoring the preparation of seismic disasters simultaneously in several relatively close potential sources of danger reduces the likelihood of missing an event, but at the same time increases the likelihood of a false alarm, since the observed anomalies are not isolated and are not contrasting in the surrounding space. It is possible to foresee the deterministic-chaotic nature of the nonlinear process as a whole, its individual stages, and scenarios for the transition from stage to stage. But the required reliability and accuracy of short-term forecasts of specific events remain unattainable. The long-standing and almost universal belief that any unpredictability is only a consequence of insufficient knowledge and that with a more complete and detailed study, a complex, chaotic picture will certainly be replaced by a simpler one, and the forecast will become reliable, turned out to be an illusion.

An earthquake is a natural phenomenon with destructive power; it is an unpredictable natural disaster that occurs suddenly and unexpectedly. An earthquake is an underground tremors caused by tectonic processes occurring inside the earth; these are vibrations of the earth's surface that arise as a result of sudden ruptures and displacements of sections of the earth's crust. Earthquakes occur anywhere on the globe, at any time of the year; it is virtually impossible to determine where and when, and what strength an earthquake will be.

They not only destroy our homes and change the natural landscape, but also raze cities and destroy entire civilizations; they bring fear, grief and death to people.

How is the strength of an earthquake measured?

The intensity of tremors is measured by points. Earthquakes with a magnitude of 1-2 are detected only by special devices - seismographs.

With an earthquake strength of 3-4 points, vibrations are already detected not only by seismographs, but also by people - objects around us sway, chandeliers, flower pots, dishes clink, cabinet doors open, trees and buildings sway, and the person himself sways.

At 5 points, it shakes even more strongly, wall clocks stop, cracks appear on buildings, and plaster crumbles.

At 6-7 points, the vibrations are strong, objects fall, paintings hanging on the walls, cracks appear on window glass and on the walls of stone houses.

Earthquakes of magnitude 8-9 lead to the collapse of walls and the destruction of buildings and bridges, even stone houses are destroyed, and cracks form on the surface of the earth.

A magnitude 10 earthquake is more destructive - buildings collapse, pipelines and railway tracks break, landslides and collapses occur.

But the most catastrophic in terms of the force of destruction are earthquakes of 11-12 points.
In a matter of seconds, the natural landscape changes, mountains are destroyed, cities turn into ruins, huge holes form in the ground, lakes disappear, and new islands may appear in the sea. But the most terrible and irreparable thing during such earthquakes is that people die.

There is also another more accurate objective way of assessing the strength of an earthquake - by the magnitude of the vibrations caused by the earthquake. This quantity is called magnitude and determines the strength, that is, the energy of the earthquake, the highest value being magnitude-9.

The source and epicenter of the earthquake

The force of destruction also depends on the depth of the earthquake source; the deeper the earthquake source occurs from the surface of the earth, the less destructive force the seismic waves carry.

The source occurs at the site of displacement of giant rock masses and can be located at any depth from eight to eight hundred kilometers. It doesn’t matter at all whether the displacement is large or not, vibrations of the earth’s surface still occur and how far these vibrations will spread depends on their energy and strength.

The greater depth of the earthquake source reduces destruction on the earth's surface. The destructiveness of an earthquake also depends on the size of the source. If the vibrations of the earth's crust are strong and sharp, then catastrophic destruction occurs on the surface of the Earth.

The epicenter of an earthquake should be considered the point above the source, located on the surface of the earth. Seismic or shock waves diverge from the source in all directions; the further away from the source, the less intense the earthquake. The speed of shock waves can reach eight kilometers per second.

Where do earthquakes most often occur?

Which corners of our planet are more earthquake-prone?

There are two zones where earthquakes occur most often. One belt begins at the Sunda Islands and ends at the Isthmus of Panama. This is the Mediterranean belt - it stretches from east to west, passes through mountains such as the Himalayas, Tibet, Altai, Pamir, Caucasus, Balkans, Apennines, Pyrenees and passes through the Atlantic.

The second belt is called the Pacific. This is Japan, the Philippines, and also covers the Hawaiian and Kuril Islands, Kamchatka, Alaska, and Iceland. It runs along the western coasts of North and South America, through the mountains of California, Peru, Chile, Tierra del Fuego and Antarctica.

There are also seismically active zones on the territory of our country. These are the North Caucasus, Altai and Sayan Mountains, the Kuril Islands and Kamchatka, Chukotka and the Koryak Highlands, Sakhalin, Primorye and the Amur Region, and the Baikal zone.

Earthquakes also often occur in our neighbors - in Kazakhstan, Kyrgyzstan, Tajikistan, Uzbekistan, Armenia and other countries. And in other areas that are distinguished by seismic stability, tremors periodically occur.

The seismic instability of these belts is associated with tectonic processes in the earth's crust. Those territories where there are active smoking volcanoes, where there are mountain ranges and the formation of mountains continues, the foci of earthquakes are most often located there and tremors often occur in those places.

Why do earthquakes happen?

Earthquakes are a consequence of tectonic movement occurring in the depths of our Earth, there are many reasons why these movements occur - these are the external influence of space, the Sun, solar flares and magnetic storms.

These are the so-called earth waves that periodically arise on the surface of our earth. These waves are clearly visible on the sea surface - sea ebbs and flows. They are not noticeable on the earth's surface, but are recorded by instruments. Ground waves cause deformation of the earth's surface.

Some scientists have suggested that the culprit of earthquakes may be the Moon, or rather, the vibrations occurring on the lunar surface also affect the earth's surface. It was observed that strong destructive earthquakes coincided with the full moon.

Scientists also note those natural phenomena that precede earthquakes - these are heavy, prolonged precipitation, large changes in atmospheric pressure, unusual air glow, restless behavior of animals, as well as an increase in gases - argon, radon and helium and uranium and fluorine compounds in groundwater .

Our planet continues its geological development, the growth and formation of young mountain ranges occurs, in connection with human activity, new cities appear, forests are destroyed, swamps are drained, new reservoirs appear, and the changes that occur in the depths of our Earth and on its surface cause all sorts of natural disasters.

Human activities also have a negative impact on the mobility of the earth's crust. A person who imagines himself to be a tamer and creator of nature thoughtlessly interferes with the natural landscape - demolishes mountains, erects dams and hydroelectric power stations on rivers, builds new reservoirs and cities.

And the extraction of minerals - oil, gas, coal, building materials - crushed stone, sand - affects seismic activity. And in those areas where there is a high probability of earthquakes, seismic activity increases even more. With his ill-considered actions, people provoke landslides, landslides and earthquakes. Earthquakes that occur due to human activity are called man-made.

Another type of earthquake occurs with human participation. During underground nuclear explosions, when tectonic weapons are tested, or during the explosion of a large amount of explosives, vibrations of the earth's crust also occur. The intensity of such tremors is not very great, but they can provoke an earthquake. Such earthquakes are called artificial.

There are still some volcanic earthquakes and landslide. Volcanic earthquakes occur due to high tension in the depths of the volcano; the cause of these earthquakes is volcanic gas and lava. The duration of such earthquakes is from several weeks to several months, they are weak and do not pose a danger to people.
Landslide earthquakes are caused by large landslides and landslides.

On our Earth, earthquakes occur every day; about one hundred thousand earthquakes a year are recorded by instruments. This incomplete list of catastrophic earthquakes that occurred on our planet clearly shows the losses humanity suffers from earthquakes.

Catastrophic earthquakes that have occurred in recent years

1923 - Japan epicenter near Tokyo, about 150 thousand people died.
1948 - Turkmenistan, Ashgabat is completely destroyed, about one hundred thousand dead.
1970 in Peru, a landslide caused by an earthquake killed 66 thousand residents of the city of Yungay.
1976 - China, the city of Tianshan is destroyed, 250 thousand dead.

1988 - Armenia, the city of Spitak was destroyed - 25 thousand people died.
1990 - Iran, Gilan province, 40 thousand dead.
1995 - Sakhalin Island, 2 thousand people died.
1999 - Türkiye, the cities of Istanbul and Izmir - 17 thousand dead.

1999 - Taiwan, 2.5 thousand people died.
2001 - India, Gujarat - 20 thousand dead.
2003 - Iran, the city of Bam is destroyed, about 30 thousand people died.
2004 - the island of Sumatra - the earthquake and tsunami caused by the earthquake killed 228 thousand people.

2005 - Pakistan, Kashmir region - 76 thousand people died.
2006 - Java island - 5700 people died.
2008 - China, Sichuan province, 87 thousand people died.

2010 - Haiti, -220 thousand people died.
2011 - Japan - an earthquake and tsunami killed more than 28 thousand people, explosions at the Fukushima nuclear plant led to an environmental disaster.

Powerful tremors destroy the infrastructure of cities, buildings, depriving us of housing, causing enormous damage to the residents of those countries where the disaster occurred, but the most terrible and irreparable thing is the death of millions of people. History preserves the memory of destroyed cities, disappeared civilizations, and no matter how terrible the force of the elements, a person, having survived the tragedy, restores his home, builds new cities, erects new gardens and revives the fields on which he grows his own food.

How to behave during an earthquake

At the first tremors of an earthquake, a person experiences fear and confusion, because everything around begins to move, chandeliers sway, dishes clink, cabinet doors open, and sometimes objects fall, the earth disappears from under one’s feet. Many panic and begin to rush around, while others, on the contrary, hesitate and freeze in place.

If you are on the 1-2 floors, the first thing you should do is try to leave the room as quickly as possible and move to a safe distance from buildings, try to find an open place, pay attention to power lines, you should not be under them in case of strong shocks Wires may break and you may receive an electric shock.

If you are above the 2nd floor or did not have time to jump outside, try to leave the corner rooms. It is better to hide under a table or under a bed, stand in the opening of internal doors, in the corner of the room, but away from cabinets and windows, since broken glass and objects in cabinets, as well as cabinets and refrigerators themselves, can hit you and injure you if they fall.

If you still decide to leave the apartment, then be careful, do not enter the elevator; during strong earthquakes, the elevator may turn off or collapse; it is also not recommended to run to the stairs. Flights of stairs may be damaged due to an earthquake, and a crowd of people rushing to the stairs will increase the load on them and the stairs may collapse. Going out onto balconies is just as dangerous; they can also collapse. You should not jump out of windows.

If tremors find you outside, move to an open space, away from buildings, power lines, and trees.

If you are in a car, stop at the side of the road, away from lamps, trees, and billboards. Don't stop in tunnels, under wires and bridges.

If you live in a seismically active area and earthquakes periodically shake your homes, then you should prepare yourself and your family for the possibility of a stronger earthquake. Determine in advance the safest areas in your apartment, take measures to strengthen your home, teach your children how to behave if children are alone at home during earthquakes.

Nadezhda Guseva

Candidate of Geological and Mineralogical Sciences

Is it possible to predict earthquakes?

Predicting earthquakes is a difficult task. Vertical and horizontal displacements of blocks of the earth's crust cause deep earthquakes, which can reach catastrophic force. Low-hazard surface earthquakes occur due to the fact that magmatic melt rising along cracks in the earth's crust stretches these cracks as it moves. The problem is that these two related but different causes of earthquakes have similar external manifestations.

Tongariro National Park, New Zealand

Wikimedia Commons

However, a team of scientists from New Zealand was able not only to distinguish traces of stretching of the earth's crust caused by magmatic and tectonic processes in the Tongariro deep fault zone, but also to calculate the rate of stretching arising from one and other processes. It has been established that in the area of the Tongariro fault, magmatic processes play a secondary role, and tectonic processes have a decisive influence. The results of the study, published in the July issue of the Bulletin of the Geological Society of America, help clarify the risks of dangerous earthquakes in this popular tourist park, located 320 kilometers from the capital of New Zealand, Wellington, as well as in similar structures in other regions of the Earth.

Grabens and rifts

Tongariro is New Zealand's Yellowstone. Three “smoking mountains” - volcanoes Ruapehu (2797 meters), Ngauruhoe (2291 meters) and Tongariro (1968 meters), many smaller volcanic cones, geysers, lakes painted in blue and emerald colors, stormy mountain rivers together form a picturesque landscape of the national Tongariro Park. These landscapes are familiar to many because they served as natural settings for Peter Jackson’s film trilogy “The Lord of the Rings.”

By the way, the origin of these beauties is directly related to the peculiarities of the geological structure of the region: with the presence of parallel faults in the earth’s crust, accompanied by the “falling through” of the fragment located between the faults. This geological structure is called a graben. A geological structure that includes several extended grabens is called a rift.

Planetary-scale rift structures pass through the median axes of the oceans and form mid-ocean ridges. Large rifts serve as the boundaries of tectonic plates, which, like the hard segments that make up a turtle's shell, form the hard shell of the Earth, its crust.

New Zealand formed where the Pacific Plate is slowly subducting under the Australian Plate. The chains of islands that appear in such zones are called island arcs. On a planetary scale, rift zones are extension zones, and island arc zones are compression zones of the Earth's crust. However, on a regional scale, stresses in the earth's crust are not monotonic, and in each major compression zone there are local extension zones. As a very rough analogy of such local tensile zones, we can consider the occurrence of fatigue cracks in metal products. The Tongoriro Graben is such a local extension zone.

In New Zealand, due to its position in a zone of active geological processes on a planetary scale, about 20 thousand earthquakes occur every year, approximately 200 of them are strong.

Magma or tectonics?

Earthquake forecasting is difficult. Faults often serve as channels through which magma moves from deep levels to the surface. This process is also accompanied by local stretching of the earth's crust. In this case, magma does not always reach the earth's surface, and in some cases it can stop at some depth and crystallize there, forming a long and narrow magmatic body called a dike.

On the surface, extensions of the earth's crust caused by the intrusion of dikes (extensions of a magmatic nature) are often morphologically indistinguishable from extensions caused by the release of stresses arising due to the movement of blocks of the earth's crust relative to each other (extensions of a tectonic nature). But to predict earthquakes, it is critically important to distinguish between these two types of stretching, because earthquakes associated with the intrusion of dikes are near-surface and do not lead to catastrophic consequences, while earthquakes of a tectonic nature can cause a lot of trouble.

It was clear that both types of extension took place in the New Zealand rift system, and in particular in the Tongoriro graben, but there were two mutually contradictory opinions as to which of them predominated.

Threat of catastrophic earthquakes

The research, undertaken by a team including Geological Survey New Zealand and Auckland and Massey universities, was carried out to find a way to distinguish between magmatic and tectonic extension and clarify the risks of large and catastrophic earthquakes in Tongariro National Park.

The scientists used a combination of methods, including relative geochronology to determine the sequence of faults in the earth's crust and analysis of historical records of volcanic eruptions. The key stage of the study was the numerical modeling of the parameters of disturbances in the earth's crust that would arise as a result of the intrusion of dikes, and a careful comparison between the model and actually observed parameters.

The study concluded that the crust in the Tongoriro graben region is stretching by 5.8–7 mm per year due to tectonic events and by 0.4–1.6 mm per year due to volcanic eruptions and dyke intrusions. This means that magmatic processes are not the main cause of crustal movements and building codes must take into account the possibility of strong and catastrophic earthquakes. And the developed methodology can be used to assess the contribution of magmatic processes to the movements of the earth’s crust in similar structures in other regions of the Earth.

Is it possible to predict an earthquake? Over the past centuries, many methods of prediction have been proposed, from taking into account weather conditions typical of earthquakes, to observing the position of celestial bodies and oddities in the behavior of animals. Most attempts to predict earthquakes have been unsuccessful.

Since the early 1960s, scientific research on earthquake forecasting has taken on an unprecedented scale, especially in Japan, the USSR, China and the USA. Their goal is to make earthquake predictions at least as reliable as weather forecasts. The most famous is the prediction of the time and place of occurrence of a destructive earthquake, especially short-term forecast. However, there is another type of earthquake forecast: an assessment of the intensity of seismic shaking expected in each individual area. This factor plays a major role in the selection of sites for the construction of important structures such as dams, hospitals, nuclear reactors, and is ultimately most important in reducing seismic hazards. In this chapter we will look at the scientific approach to predicting the time and location of earthquakes, and we will describe methods for predicting strong ground vibrations in Chapter 11.

As stated in Chap. 1, the study of the nature of seismicity on Earth over a historical period of time made it possible to predict those places where destructive earth events may occur in the future

Shaking. However, the chronicle of past earthquakes does not make it possible to predict the exact time of the next catastrophe. Even in China, where between 500 and 1,000 devastating earthquakes have occurred over the past 2,700 years, statistical analysis has not revealed a clear periodicity of the largest earthquakes, but has shown that major catastrophes can be separated by long periods of seismic silence.

In Japan, where there is also long-term earthquake statistics (Fig. 1), intensive research on earthquake forecasting has been carried out since 1962, but so far they have not brought any success. (However, it must be borne in mind that in recent years no major destructive earthquakes have occurred on the Japanese Islands, although many weak tremors have been noted.) The Japanese program, combining the efforts of hundreds of seismologists, geophysicists and surveyors, has led to the receipt of a huge amount of diverse information and has made it possible to highlight there are many signs of an impending earthquake. One of the most remarkable precursors of earthquakes among those studied so far is the phenomena noted on the west coast of the Japanese island of Honshu. Geodetic measurements carried out there showed (see graphs in Fig. 2) that in the vicinity of the city of Niigata there was a continuous rise and fall of the coastline for about 60 years. In the late 1950s, the rate of this process decreased; Then, during the Niigata earthquake on June 16, 1964, a sharp drop of more than 20 cm was noted in the northern part of this area (near the epicenter). The nature of the distribution of vertical movements, shown in the graphs in Fig. 2, was found out only after the earthquake.
But should such major changes in elevation occur again, this will undoubtedly serve as some caution. Later in Japan, a special study of historical earthquake cycles in the vicinity of Tokyo was carried out, and local measurements of modern crustal deformation and earthquake frequency were also carried out. The results have led some Japanese seismologists to suggest that a repeat of the great Kanto earthquake (1923) is not currently expected, but that earthquakes cannot be ruled out in neighboring areas.

Since the beginning of this century, if not earlier, assumptions have been made about different types of “trigger mechanisms” capable of causing initial movement at the source of an earthquake. Among the most serious assumptions are the role of severe weather conditions, volcanic eruptions, and the gravitational pull of the Moon, Sun, and planets). To find such effects, numerous earthquake catalogs were analyzed,

including very comprehensive lists for California, but no definitive results were obtained. For example, it has been suggested that since every 179 years the planets find themselves approximately in one line, the resulting additional attraction causes a sharp increase in seismicity. The next such planetary alignment is expected in 1982. The San Andreas Fault in southern California has not produced destructive seismic shocks since the Fort Tejon earthquake in 1857, so the impact of this "planetary" trigger on the said fault in 1982 could be considered particularly likely. Fortunately for California, this argument is seriously flawed. Firstly, world earthquake catalogs show that in past episodes of such an arrangement of planets: in 1803, 1624 and 1445, no increase in seismic activity was observed. Second, the additional attraction of relatively small or distant planets is negligible compared to the interaction between the Earth and the Sun. This means that in addition to the 179-year period, we must also consider the possibility of many other periodicities associated with the joint action of the largest celestial bodies.

To provide a reliable forecast, such as predicting the phases of the moon or the outcome of a chemical reaction, a strong theoretical basis is usually necessary. Unfortunately, at present there is still no precisely formulated theory of the origin of earthquakes. However, based on our current, albeit limited, knowledge of where and when seismic tremors occur, we can make rough predictions about when the next largest earthquake can be expected on any known fault. Indeed, after the earthquake of 1906 G.F. Reed, using elastic recoil theory (described in Chapter 4), stated that the next major earthquake in the San Francisco area would occur in about a hundred years.

Briefly, his arguments boiled down to the following. Geodetic measurements made across the San Andreas fault before the 1906 earthquake showed that the relative displacement on opposite sides of the fault reached a value of 3.2 m over 50 years. After elastic recoil occurred on this fault on April 18, 1906, the maximum the relative displacement was about 6.5 m. Having made an arithmetic calculation, we obtain: (6.5:3.2)-50 = 100. Consequently, 100 years must pass before the next strongest earthquake. In this calculation we must make the rather weak assumption that regional deformation occurs uniformly and that the properties of the fault that existed before the 1906 earthquake were not changed by this earthquake. Prudence also requires us to consider that along the San Andreas Fault in the coming centuries there may not be another earthquake with a magnitude of 8.25, but a series of tremors of more moderate magnitude.

Currently, a lot of experimental work is being carried out, various phenomena are being studied (listed in the next section), which may turn out to be harbingers, “symptoms” of an impending earthquake. Although the attempts at a comprehensive solution to the problem look quite impressive, they provide little reason for optimism: the forecast system is unlikely to be practically implemented in most parts of the world in the near future. In addition, the methods that now seem to be the most promising require very complex equipment and a lot of effort from scientists. Establishing networks of forecasting stations in all high seismic risk areas would be extremely expensive.

In addition, one major dilemma is inextricably linked with earthquake forecasting. Suppose seismological measurement data indicates that an earthquake of a certain magnitude will occur in a certain area within a certain period of time. It must be assumed that this area was previously considered seismic, otherwise such studies would not have been carried out on it. It follows that if an earthquake actually occurs during the specified period, it may turn out to be a mere coincidence and will not be strong evidence that the methods used for the forecast are correct and will not lead to errors in the future. And of course, if a specific prediction is made and nothing happens, this will be taken as evidence that the method is unreliable.

There has been a recent increase in earthquake forecasting activity in California, resulting in the formation of a scientific panel in 1975 to evaluate the reliability of forecasts for the state emergency management agency and, therefore, the state governor. The Council plays an important, but not decisive, role in determining the real meaning of certain data and statements of individuals or groups (usually the statement of a seismologist or seismologists working in a government or university laboratory). The board's recommendations do not address the timing or content of public hazard alerts issued by state authorities. As of 1978, this council had only on two occasions had to deal with issues related to earthquakes expected to occur in California.

In Western countries, negative as well as positive consequences of the prognosis have been studied. If, for example, in California it was possible to confidently predict the time of a major destructive earthquake about a year before the expected date and then continuously refine it, then the number of victims and even the amount of material damage from this earthquake would be significantly reduced, but public relations in the pleisto-seist region would be disrupted and the local economy would collapse. The most important social and economic consequences of such a forecast are illustrated in Appendix 6 later in this chapter. Of course, without practical testing, such estimates look very speculative; The overall consequences will be highly complex, as the responses of the public, public and private sectors may be quite different. For example, if, following a scientific forecast and official warning, the public demand for earthquake insurance increases sharply, this will undermine its availability and have a temporary but extremely serious impact on the value of real estate, land and construction, on the value of deposits and employment. The population, scientists and government officials still have a very vague idea of all these problems.