Share this article with friends
Dramatic reports of earthquakes, big and small, are in the news from different parts of the world as often as not. But the event which occurred in Gorny Altai in the autumn of 2003 passed away almost unnoticed. And this was only natural because there were no casualties or material damage there. But as different from the general public, the quake aroused tremendous interest on the part of experts. Subterranean strikes were mighty (three of them with strength of 6, 6.5 and 7.5 points) and numerous (from September 27 to October 15, 2003 there were 74 shocks with M of more than 3.5). And the seismic catastrophe that occurred in Iran on December 26 of the same year took a toll of more than 40 thous. lives and reduced to rubble nearly the whole of the ancient town of Bam. And it was not so strong (M = 6.8) although its focus was at the same depth as in Altai - of about 30 - 50 km. It was simply located right under the residential districts consisting of not very durable structures.
Interesting details about the Gorny Altai event were supplied by casual eyewitnesses who happened to be on the spot at that time: staff members of the Institute of Geology of the RAS Siberian Branch - Igor Novikov, Yevgeny Vysotsky, Alina Agatova and Anna Gibsher. In their report published in the NAUKA V SIBIRI (Science in Siberia) newspaper they stressed that "the absence of human casualties in the recent quakes is explained by several reasons. These include low population density in the region and colossal anti-seismic strength of the small local homes made of logs and timber (we saw one such house without any visible damage located in the very center of the zone and only 700 m away from the landslide). And it was sheer luck that no one perished in rock slides, landslides or tectonic fractures."
In an introduction to the article, however, the situation is described in not so accurate terms-that the earth shocks struck "on relatively quiet grounds, like thunder from a clear sky". Indeed, there is no denying the fact that the "elements" strike us most often as a complete surprise. But this time around a long-term seismic forecast had been with us for quite some time and with relative accuracy: the region was marked on the maps as a dangerous zone where quakes of 9-points could be expected. And this was very close to what really happened there. And the absence of a short-time warning is really not surprising because of the lack of the appropriate methods*. And there are no necessary geophysical stations in that region.
Eyewitnesses of the tremor had seen some of the "early warnings - the road they were traveling along was often barred by piles of rock and sand and screes. On that particular occasion landslides of up to one kilometer across and with a volume of up to 300 mln m 3 were formed deep under the surface. Rifts of sediments in flood plains and river terraces were 145 m long and up to 5 m wide. Huge boulders located on the surface were "shrugged off' from their places at distances of up to one meter.
And one would like to specially mention one interesting phenomenon. The aforesaid geologists observed jets (gryphons) of ground water which carried to the surface hundreds of cubic meters of sand and clay forming small lakes and "huge gaping vents of mud volcanoes". In actual fact what they were dealing with were not mud volcanoes, but more rare hydrovolcanoes. The difference between them is appreciable. The former mainly eject gases rising from great depths (of several kilometers). They occur, for example, in the Crimea, Northern Caucasus and the Apsheron Peninsula and often signal the presence of oil-and-gas deposits. Others occur under the pressure of artesian waters of shallow location (20 - 30 m) which "break through" the surface under the impact of seismic shocks.
Such matters have to be mentioned now because up to this day many geologists draw no line between so different natural phenomena. This is despite the fact that some 200 years ago the German Encyclopaedist and Honorary Member of the St. Petersburg Academy of Sciences, Prof. A. Goumboldt, in his book "Pictures of Nature" singled out "salses, or mud volcanoes, which eject mud, asphalt and hydrogen" and also "watery and fiery volcanoes". But the scientist's classification of these natural phenomena remained unnoticed by most specialists.
In all probability hydrovolcanic signs can serve as indicators of major seismic shocks as was vividly demonstrated by the recent earthquake in Gorny Altai.
And the aforesaid geologists were also able to observe one more characteristic process produced by subterranean forces. "Field radiation of the biggest block landslide in the zone of 9 to 10 points - they write-demonstrated that landslides of this magnitude in
* See: V. Morgunov, "Earthquake Forecasts for Tomorrow", Science in Russia, No. 1, 2004. - Ed.
perennially frozen rock develop only as a result of seismic shocks. Taking place right in front of us was degradation of frozen ground and transformation of block slide into a stream-slide whose identification is practically impossible as seismogenic one without the knowledge of the history of its formation".
Expert studies carried out right after this major tremor are of great scientific and practical value. Within a relatively short span of time Nature will start "healing the wounds": hydrovol-canoes will cease to exist and their funnels will be filled up with sand-and-mud mixture; the gaping crust fractures win disappear as well as swell bars produced by shifts of crystal blocks; perennially frozen rock will turn into mudstreams. And then geologists and seismologists will have to try and reconstruct- with great efforts and considerable inaccuracies - the events of the relatively recent past and try and assess the scale of risk for engineering structures erected in some concrete local conditions (on river terraces, in canyons and mountain slopes) within the limits of seismohazardous zones. In the opinion of the authors of the publication, the subterranean hurricane in Gorny Altai can be regarded as a stern warning which has to be considered in the course of the economic development of the territory. And for experts, this has been a "precious gift"-a set of diverse scientific data.
"Analysis of this information-says the article-will not only help improve the regionalization (zoning) of Altai according to the scale of the seismic threat, but will make it possible to have a deeper insight into the processes of the latest inter- continental tectonic activities and orogenesis (mountain building), which are one of the causes of such seismic events".
NAUKA V SIBIRI (Science in Siberia), 2003
Prepared by Rudolf BALANDIN
Permanent link to this publication:
LRussia LWorld Y G