From the Editors. The phenomenon of increase of seismic activity during the filling of several large reservoirs, observed in recent years [26], has raised a new complex problem in the hydraulic engineering field. This problem is especially timely for the Soviet hydraulic engineers in connection with the design and construction of several high-head hydraulic structures in seismic regions. It is evidently necessary to take into account in design the possibility of the development of seismicity caused by such activities. This problem is highly complex because of the fact that at the present time there are no clear concepts about the mechanism of the development of such earthquakes. The author of this article, which is being published for discussion, presents several considerations which, in his opinion, can explain the mechanism of earthquakes associated with reservoir construction. The author's pronouncements do not correspond always to the present-day level of geotectonics and seismology, but many of his ideas may be of interest and should lead to discussions of this important problem.Many cases of occurrence of seismic activity during the filling of large reservoirs in regions which had been previously considered as aseismic [8 and 18-22] have raised the problem of the study of the interrelation between these phenomena. This problem was discussed at the Ninth and Tenth International Congresses on Large Dams and has been included in the agenda for the llth Congress. A special group of experts from the UNESCO organization is engaged in the study of the problem of earthquakes connected with artificial reservoirs.Despite a large number of cases of induced seismicity, at the present time there is no clear concept about the mechanisms governing its development. On the other hand, similar characteristics of the "ordinary" 'earthquakes which occur during the filling of reservoirs as well as the occurrence of induced seismicity when water is pumped into deep holes provide reasons for examining more carefully the mechanism of the development of "ordinary" earthquakes from the standpoint of the role played by water in this process. A very characteristic concept on this problem was formulated by the well-known seismologist Rothe: "... The exact mechanism of the development of strong artificial earthquakes is incomprehensible, although it is clear that, just as in natural earthquakes, in this case there is in the weak zones a liberation of energy accumulated within a limited rock volume. Although the origin of natural earthquakes is not known, the relation between artificial earthquakes and the weight of the water is evident. It is hoped that the study of artificial earthquakes will help to solve the problem of the prediction of earthquakes in the general case" [19].According to current theories, the factors considered as the potential causes of earthquake development can have very complex interrelations. However, in the final analysis all of them lead to variations in the stress state of the rock masses in the earth's crust...
In tunneling and concreting four inclined water-intake conduits of the Aswan dam in the United Arab Republic, the conditions for removal of the excavated rock were rather complicated. This was due to tight deadlines for completion of the inclined tunnel sections and the necessity to perform this work while the construction work as a whole was in high gear due to simultaneous work on the intake structure and on the branched tunnel sections at the power house.The tunnels had circular cross sections 15 m in diameter, and clear sections 17 m in the rough, with 1 m thick reinforced-concrete linings. The excavated sections were 30 to 35 m long in each tunnel. The total quantity of loose rock that had to be removed was 54,000 m s. The rock formations encountered were granites and granitic gneisses of medium hardness, with layers of soft magmatites and pegmatites.
It is presently generally recognized that under certain conditions the creation of reservoirs, injection of water into deep wells, and the pumping out of oil and gas are the cause of a sharp increase of seismic activity.Such technogenic ("induced," "stimulated") earthquakes differ in no way from "ordinary" ones. The mechanism of this phenomenon, just as the focal mechanism of an "ordinary" earthquake, is not clear.In the given case we are dealing with a paradoxical situation. On the one hand, it would seem, technogenic earthquakes only add vagueness to the already unclear problem of the focal mechanism.But, on the other hand, the very fact of the effect of technical factors on the focal mechanism (which not long ago was completely denied) and examples of their various combinations make it possible to pose more clearly the question about studying the focal mechanism in the general case. In this regard we can quote the statement of the prominent French seismologist Rothe:"... The exact mechanism of strong artificial earthquakes is not understood, although it is clear that, just as in the case of natural earthquakes, in this case the energy stored in a limited volume of rocks is released through weakened zones. Whereas the origin of natural earthquakes is unknown, the relation of artificial earthquakes to the weight of the water load is obvious."It can be hoped that a study of artificial earthquakes will help to solve the problem of earthquake prediction in the general case." But if we can affect seismicity toward its increase, then on the basis of general principles we can pose the question about developing technical measures not allowing its increase during construction of dams and in other similar situations.The next, completely logical step will be the development of measures to reduce seismicity under ordinary conditions in earthquake-prone regions.The primary and most vital task will be, of course, the organization of an automatic earthquake warning service on the basis of a system of instruments (measuring the water level, temperature, etc.) installed in the region of a potential focus. Attention is called to the fact that such an automatic warning service basically differs from the presently existing practice of earthquake prediction. However, for this purpose it is necessary in principle to change the approach to a study of this problem.For all the complexity of the question about the probability of earthquakes, a passive approach developed in a study of this problem, dooming science and practice just to the collection of information about earthquakes occurring with the timid hope in the distant future of establishing some sort of earthquake prediction systems. As regards an automatic warning system and especially an earthquake counteraction system, such an undertaking is presently practically completely precluded by this approach.Unconditionally, equipping of a large number of seismographic stations with computers will increase the quantity of observation data and simplify their processing, but it will not...
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