Author: by Andrei NIKONOV, Dr. Sc. (Geol. & Mineral.), RAS Otto Schmidt Joint Institute of Physics of the Earth

Articles in this rubric reflect the opinion of the author.- Ed.

For quite a long time, seismic activity in Russia's European part has not been considered an issue to merit the attention of the scientific community. Researchers were more concerned with other natural, and particularly, human-made disasters. Improbable as it seems, the threat of earthquakes is not as nebulous as it is thought to be in this enormous, heavily populated region honeycombed with underground ducts and sewage systems and packed with vulnerable high-tech industries. Natural seismic tremors, whenever they are felt on the Russian Plain, are more often than not ripples caused by earthquakes thundering elsewhere, very far from Russia. They can, even if rarely, cause some havoc here.

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COOKING IN THE CARPATHIANS

Jolts rolling over Ukraine or Russia have been so far harmless, for all the extensive areas they have involved and bouts of panic they set off. In their vast majority, tremors ranging from 6 points in the south to 4 points in the north of Moscow are generated by strong and very strong Carpathian earthquakes centered on the so-called Vranica deep-focus zone in Romania.

Four quake waves reached the Russian Plain in the 20th century-in 1940 (twice), 1977, 1986, and 1990 (the first two waves rolled north as far as St. Petersburg and Nizhni Novgorod). The strongest tremors felt on nearly half of Russia's western areas in the 19th century were registered in 1802, 1829, and 1838. Weaker ones

occurred in between these major shocks. These earthquakes were studied professionally, and maps were even drawn up to show magnitude distribution that can today be used in estimating the possible effects of earthquakes on sensitive industries, including nuclear power plants. Pinpointing the exact time an earthquake may strike is still a problem nowhere near resolution. That is why scientists in many countries have in recent years focused on measuring average recurrence rates of destructive quakes in different regions. In their efforts, they can benefit much from earthquake studies in countries of long history and longstanding construction and record-keeping traditions.

The Carpathians hardly fit this qualification, even though this mountainous region was a province of the Roman Empire in the 2nd and 3rd centuries A.D. No major building projects were ever undertaken there, and written records are but few. In the centuries that followed, at least to the 16th or 17th centuries, history chronicling in the region was not much better. A report survives, by sheer luck, of a strong earthquake that surprised the Huns under Attila on the Carpathian Plain in the mid-5th century

The history of strong deep-focus earthquakes here in the last thousand years can, fortunately, be reconstructed with as much, if not more, accuracy and reliability as in any other written record-rich area of Southern Europe. Russian chronicles going back to at least the 10th century deserve much of the credit for this.

It is interesting, of course, how tremors, felt but very weakly in Russia's European part, originating far from it, in Romanian mountains, or more exactly, under the mountains, can tell anything worthwhile? The answer is simple enough. The enormous depth of Vranica earthquake centers (between 80 and 150 km) and the specific structure of the lithosphere under the Russian Plain (riddled with wave- guides) are the principal factors allowing seismic waves from Vranica earthquakes to travel very far north and northeast from their birthplace. In this respect, good reference points are provided by well-studied Carpathian earthquakes in the 19th and 20th centuries, which provide a fairly accurate yardstick to determine the magnitude, propagation pattern, and aftereffects of past earthquakes. From this angle, Russian chronicles are a source of information that can hardly be overestimated.

EARTHQUAKES IN CHRONICLES

Having identified the problem, it would be interesting to take a look at some specific characteristics of Russian chronicles, including, in the first place, their continuity for many

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centuries, reliance on some local records to make up composite manuscripts, borrowings and adaptation of reports from previous manuscripts.

In interpreting these records, we have to allow for the level of knowledge at a particular time in the past, concepts and beliefs existing at the time, imperfections of the calendar, and much else. In respect of earthquakes in particular, chronicle records about them can be considered relatively complete (so far as the reports, rather than the descriptions of particular events, are concerned). Let me note in passing that trembling (shaking) of the earth underfoot, even very weak tremors, were, along with other natural events, received by people as an extraordinary, not accidental, phenomenon, and as a warning from above about impending troubles and disasters (crop failure, enemy invasion, death of the ruler, and so on). It is for this reason that chroniclers strove to record them all without missing a single one.

Their records have long been appreciated due to this documentary aspect. The first Catalog of Earthquakes in the Russian Empire compiled for Russia's European part by Ivan Mushketov and Alexander Orlov in 1893 drew fairly extensively on old chronicles. In our time, a fine summary of such events is provided, alongside a survey of weather and climatic anomalies, in the book "A Thousand-Year Chronicle of Unusual Natural Phenomena" (put out in 1988) by Yevgeni Borisenkov and Vassily Pasetsky. Its conclusions are briefly as follows:

Russia was spared by earthquakes in the 14th century, but had more than a fair share of them in the 12th. This period deserves a closer attention, though. Fourteen quakes occurred between the late l lth and early 13th century (for comparison, there were only four major earthquakes in the 20th century). How come? Did the seismic pattern change? Or were data reports irregular? This is a crucial question. The answer may help establish laws governing energy release in the Carpathians.

Most likely, the "shortfall" of subterranean shocks throughout the 13th and 14th centuries can be attributed to the shortage of records that are available to us. Indeed, at the time of the Mongol invasion and, then, under the rule of the Golden Horde keeping records of earthquakes took a far second place to things much closer to home.

What kind of explanation can be offered for the 12th century, when there was an abundance of earthquakes? First, it may safely be assumed, without any allowances, that a single event could be recorded twice, for different, yet closely spaced, years (so the total number of earthquakes goes up). Second, as we said earlier, composite manuscripts were based on different sources, including local chronicles. Local time reckoning systems differed from place to place, sometimes by as much as a year or two. Manuscript copyists paid little attention to this at times. The probability of a single event being recorded under different years rises when the chronicle refers to any other uncommon natural phenomena simultaneously (for example, "a dragon from heaven"), or when earthquakes occurring in two consecutive years are assigned closely spaced dates, sometimes with an interval of a few days only. Allowing for this possibility, we can justifiably combine several pairs of adjacent years, for example, 1088 and 1093, 1107 and 1109, and 1126 and 1127. Moreover, the first pair can safely be struck out, because, according to the chronicle, "the earth shook" after "a great dragon descended from heaven", that is, as we see it, a meteor streaked across the sky.

If we leave out such instances, the number of earthquakes through the 12th century may be counted on the fingers of one hand. By analogy with confirmed data for the past two centuries, shocks may be considered to originate in the Carpathian mountains if they were felt in Kiev (the Kievan Land), and that was certainly the case, if trembling was recorded in a Russian town or principality lying farther north. Tested by this measure, the 1126-1127 pair is wrongly placed in the Kiev Land, because neither the Ustyug record for 1474 to 1516 nor the Ipatiev Chronicle of the early 15th century specifies the exact location of the events. Two earthquakes, in 1100 and 1195, only are referred to as occurring in Kiev in the 12th century And the remaining ones? The reports for the first 30 years of the century, 1107, 1117, 1122/1124, 1126/1127, and 1131 appear to be particularly suspicious to be true. Five earthquakes in

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a row in a single focal zone, isn't it a little too many? Or what?

REREADING THE CHRONICLES

For a start, two earthquakes. One in 1107. In a foreword to their Catalog, Mushketov and Oriov wrote, "The oldest fact of this sort is dated the year 1107, when an earthquake foreshadowed the death of the wife of Grand Prince Vladimir." On this cue, seismologists have to this day cataloged this tremor as having occurred in Kiev and, therefore, place it in the Carpathians. The 1377 Laurentievskaya Chronicle, followed by the Typographskaya Chronicle, second half of the 15th century, and the Vladimirsky Chronicle, 12th and 13th centuries, do not specify the location in their records for 1107:

"... In the same winter, on February 5, the ground shook at night before dawn," while, as the Tale of the Bygone Years (the 1110s) says, "And on February 5 ground trembled in the night before dawn."

Here, contrary to the common practice of indicating, directly or indirectly, the Kievan Land as the site of tremors, the documents fail to specify the location. This looks suspicious, at least. But, in principle, it is possible to put the finger on the place where anything referred to in the chronicles occurred. For example, the reference to an earthquake in the Tale of the Bygone Years concludes an entirely separate passage, set apart from the preceding text describing the Russian princes' action against "Aepa and the other Aepa". Aepa was the name of a Polovtsian khan, who, according to the same source, roamed with his tribe and some other Turkic-speaking tribes, between the Sula and Horol rivers in the northeast and the Don River in the southeast in the late 11th and early 12th centuries.

In 1107, three Russian princes not merely took "action" against the Polovtsi, but went to the nomads to "make peace" with them and there, "on the 12th day of the month of January" celebrated the weddings of two princes. All this means that, first, the Russians visited a Polovtsian permanent winter camp and, second, they stayed with the Polovtsi for more than a week. The Polovtsi used to pitch winter camps, most likely, in the south, at some point on the Don River, and/or in the steppes descending toward the Sea of Azov, through which ran the well-beaten road to Tmutarakan, an old Russian city on the Taman Peninsula in the 10th to 12th centuries. The report of an earthquake at a specific date and time of the day, immediately after the wedding day, leads to a logical conclusion that the chronicler was well aware of the particulars of this historic event.

As may easily be assumed, the seismic tremors on 5 February, 23 days after the wedding on January 12, could occur while the Russian princes were still in the khan's camp or on the way home, that is, in the Azov steppes or on the Don. For otherwise, the chronicler would not have itemized the successive events in such particulars, and the earthquake would have been localized to Kiev or associated with any other events in the Russian central city, that the chronicler put to the same year.

We know, however, that Carpathian earthquakes are not felt, normally, on

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the Sea of Azov or farther north, on the Don. The area only weakly responds to strong earthquakes in the Crimea, like the one in 1927, for example, and, theoretically, can reverberate moderately from powerful shocks, in the Anapa focal zone, on the northeastern shore of the Black Sea, that is, in the vicinity of the old Tmutarakan. It is very likely, therefore, that the Tale of the Bygone Years refers to the 1107 earthquake that occurred at present-day Anapa, rather than in the Carpathian Mountains.

The second earthquake, in 1117, is commonly supported by a single phrase from the Tale of the Bygone Years or from the 15th century Muscovian Book of Chronicles, "In the same year on September 26 the ground shook." Without any second thought, the event is, also commonly enough, in Kiev. But what, in fact, does a single phrase wrested out of its context tell us?

Let us read over the Tale, which ends exactly on the year 1117. The most important events of the year take only half a page. The roll of princely and public affairs in Novgorod, Vladimir and Kiev is suddenly broken in the middle to make room for three short entries, seemingly out of place here, but actually a peculiar triplet of facts, "In that same year the Belaya Vezha people came to Russia. Also in that same year Vladimir married Andrei to Tugorkan's granddaughter. And in the same year on September 26 the ground shook." Plain affairs, simple news, of which there is plenty in the chronicle. Not quite so. The phrase refers to the residents of Belaya Vezha, or Sarkel, an urban center on the Don in the 9th to the 12th centuries. And to Tugorkan, a famous Polovtsian khan; the marriage of the Russian prince's son to the khan's granddaughter was a significant event meriting mention in the

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chronicle. What is, though, common for these three entries? They are related to Russia's remote southeastern margins and the areas under the rule of the Polovtsi. And, of course, emphasize the importance and rareness, if not uniqueness, of the event-arrival of the Belaya Vezha people. Not a bunch of traders, armed men or ambassadors, but residents of Belaya Vezha. What brought them there? Had the reason been important for Kiev, the Russian capital, the chronicler would have named it. They could not be fleeing from the Polovtsi-not a word about that in the chronicle. Rather, the contrary is true-the Russian prince's son marrying Tugorkan's granddaughter, a sign of complete peace, in that year at least, with the Polovtsi.

And, lastly, the final statement, "And in the same year on September 26 the ground shook." No clue as to the whereabouts. It is clear, though, that is does not refer to Pereyaslavl, near Kiev, or Minsk, which is utterly unfamiliar with earthquakes, at least of a magnitude warranting the chronicle's attention.

As well as winding up the chronicle of events described in the Tale of the Bygone Years, the earthquake entry ends the Polovtsian triplet. The earthquake it mentions, therefore, occurred on the far-off fringes of the Russian land, as it was at the time. If we accept this for a fact, we have to dig for a conceptual link between the three events that got into the chronicle. The news of the earthquake (including its exact date) could certainly be brought to Kiev by the wedding train. This is unlikely, though. Minor trembling could be overlooked amidst the merry-making attending the royal marriage. And more, it could frighten the revelers and spoil the wedding, in which case it would have deserved special comment. Most certainly, this news could be brought by the Belaya Vezha people.

As we now know, the trembling caused by strong jolts in the Carpathian center alone was felt (and chronicled) in Kiev No records were left of this one in Kiev However, great earthquakes do occur, even though rarely, on the Sea of Azov, as we can judge by the traces of seismic havoc caused in the ancient Tanais, which stood in the mouth of the Don River in the 3rd century B.C. to the 5th century A.D. It is reasonable to assume that the news of a violent earthquake at Belaya Vezha could be brought to Kiev by that hapless city's residents. Their coming to Kiev was, of itself, an utterly extraordinary event that was explained by a natural disaster, rather than by maltreatment at the Polovtsi's hands. The chronicle in Kiev made no note of the disaster, because it never was: some 700 or 800 km is too large a distance for a 9- point earthquake on the Lower Don to be felt in Kiev

There is still uncertainty about the earthquakes chronicled for the years 1122,1126/1127,1131, and 1170. One thing is clear, though: there is no reason to attribute them to the influence of the deep-focus Carpathian centers, as seismologists continue to do to this day.

The long-held belief that Russia was shaken by an uncommonly large number of earthquakes, or that, at least, the Carpathian focal zone was inordinately active at that time, has been overturned.

WHEN WILL IT STRIKE AGAIN?

The results of our studies and analysis are remarkable in many respects.

Above all, this applies to Carpathian earthquakes in the Vranica focal area. Now we have added proof that seismic energy is released fairly uniformly over 100 years on average. At Kiev's latitude, energy release is manifested in trembling four or five times every hundred years with a magnitude of 5 to 6 points. At the latitude of Moscow, echoes of Carpathian quakes normally do not exceed 3 or 4 points and occur two or three times in the same period.

How are such jolts dangerous for large cities, and particularly for megalopolises with their blocks of high rises and modified soils and hydrogeological conditions? This question needs special study. It is significant, however, that given the above-described behavior of the Vranica zone, it is to be believed that two or three considerable seismic events are to be expected every year in such major cities as Kiev, Kharkov, and Moscow of power in the range of 5 to 6 points, in the two first-named cities, and 4 points in Moscow in centuries to come. They can occur at intervals of several decades apart, or may follow in less than ten years. We cannot tell yet when an earthquake strikes, but it certainly will, sometime.

Another result with equally important implications is the possibility, confirmed by our studies, of very strong (probably, at least 8 points) earthquakes in areas where they could least be expected because of location, and they can be quite destructive. Meanwhile, a majority of earthquake authorities will hardly concede that the threat of quakes is, in this sense, hanging over the northern Azov and Lower Kuban areas. True, there is no cause for panic as yet. The existence of a long-term seismic potential in these areas, never plotted on specialist maps in the past, is an academic reality, requiring closer study. Destructive calamities may occur here at intervals of several hundred years (the reason why we know nothing about them). This possibility must put us on our guard, were it only because this area has a nuclear power plant at Rostov, a gas pipeline running across it to Turkey, and Russia's only major Black Sea port, Novorossiisk. A new oil-handling terminal, not to mention the children's resort of national importance at Anapa, are not far away

Nature has been taking revenge on man for his imprudence in many areas. We have not predicted many seismic catastrophes, because we have been unable to, for yet another reason-we have not studied man's previous brushes with disaster thoroughly enough. Today, the international community of seismologists has owned up its failings and identified priorities, and has launched specialized programs to study major earthquakes of the past ages.

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