NATIONAL SCIENTIFIC CONFERENCE "MODERN SEISMOLOGY: ADVANCES AND PROBLEMS"
The conference "Mordent Seismology: Advances and Problems" was held in Moscow on October 7 –9, 1998 under sponsorship of Russian Basic Research Foundation, National Geophysical Committee of RF and Scientific Council of RAS for IDNDR.
50 years have passed in 1998 since the catastrophic earthquake in Ashkhabad and 10 years since the no less lamentable Spitak earthquake. Both earthquakes induced considerable changes in seismological research in Russia. After 1948, the quest for earthquake precursors was initiated and a Unified System of Seismological Observations in the USSR was developed. The Spitak tragedy triggered a fundamental reassessment of notions about the level of seismic hazards on the territory of the CIS and initiated the compilation of a New Map of Seismic Zoning of Russia and the Adjacent Territories.
At present, a large amount of new data on the deep structure and dynamics of the Earth is collected, the mathematical and physical-geological models of the seismic process development are evolved, and new methods are elaborated for estimation of seismic risk and earthquake prediction. The seismic risk rapidly grows with industrial and civic construction in earthquake prone regions also as a result of technogenic effect on seismicity. With these problems in view for further progress in seismological science, an All-Russia Forum of scientists-seismologists became expedient.
The main goal of the conference "MODERN SEISMOLOGY: ADVANCES AND PROBLEMS" was to discuss the most pressing problems of seismological science and to work out a strategy for further fundamental and applied research. The three sessions of the Meeting were dedicated to three topics:
A brief review of results of the conference that were made by convenors is presented below.
Fourteen scientific papers and communications and seven poster papers were presented on "The theory of seismic process". Most of them summarized theoretical and experimental research, and six papers were dedicated to the nontraditional and acute problems in seismology. The larger part of the papers discussed, in different measure, the physical models of formation of seismicity, its numerical modeling and mathematical description.
A.A. Solov'ev (International Institute of Earthquake Prediction Theory and Mathematical Geophysics, RAS) presented a model of the lithosphere plates movement as a set of discrete shifts that are interpreted as earthquakes. Despite a rather simple model, the author showed the grouping of earthquakes in time and the formation of certain spatial regularities on artificial catalogs. An approach to the real block medium will provide in future the possibility to use mathematical modeling not only for a better understanding of the process, but for the long-term earthquake prediction as well.
V.B. Smirnov studied the fine fractal properties of the seismic process and generalized them as simple quantitative relations that develop a simplified model of the seismic flow process. It allows him to connect the main characteristics of seismicity and of the process of destruction of the medium within the frame of more extensive notions about self-similarity.
B.V. Levin and E.B.Chirkov reported the results of their research on the regularities in the latitudinal distribution of earthquake foci and described the obtained general regularities which they attribute to the processes associated with the Earth's rotation and to tectonic movements occurring against the background of this rotation. The influence of the Moon on the Earth is shown as manifested in the characteristic latitudinal distribution of seismicity.
A.V. Nikolaev gave a general analysis of directed seismicity in a wider perception of this process, i.e., the effect of endogenous and exogenous factors, both natural and technogenic. It was shown that owing to the high sensitivity of the earthquake preparation processes to external activity, particularly at the final stage, a possibility appears to not only predict an earthquake by a higher sensitivity of the focal zone to external effects, but also to influence the process of preparation by an man-made activity in combination with the natural one.
This proposition is in agreement with the studies carried out by N.T. Tarasov and N.V. Tarasova, who experimentally confirmed a significant and peculiar influence of the subsurface nuclear tests in the Semipalatinsk test-area on the earthquakes in the Garm region of Tadjikistan. It is also in agreement with the poster paper presented by N.T.Tarasov , N.V.Tarasova, A.A. Avagimov and V.A. Zeigarnik, who showed the fact of the effect of the powerful MGD-generator impulses on seismicity in Tien Shan; in this case the same methodical approach was used as in the study of the effect of subterranean nuclear tests.
I.A.Garagash compiled a new theoretical model of the seismic process, which takes into account the saturation of rocks with water and the role of water in the process of deformation of the environment. The dehydration of the lower crust results in the long-term (about 1000 y) changes in the stress state and seismicity.
The paper by E.M. Chesnokov, Yu.A. Kukharenko and P.Yu. Kukharenko on seismic emissions in thermoactive areas belongs to the same topic of study of the seismic process. The theoretical research has yielded quantitative relations allowing to estimate the role of thermal effect on seismic emission; apparently, this result can be generalized for weak seismicity as well.
A.V. Vikulin and A.G. Ivanchin described a model of seismic energy discharge by means of a rotating block, which was applied to the analysis of seismicity in the Pacific Ring. The well-known regularities in the migration of strong earthquake foci were confirmed, as also the mechanism of maintenance of the crust in the stress state by the rotating movement of lithospheric plates.
Another group of papers was dedicated to the study of processes in the source.
S.V. Sharov and L.N. Solodilov constructed a model of the focal process development using the current notions about the nonequilibrium thermodynamics; the authors established a three-stage character of the seismogenic process and determined the physical differences in weak and strong earthquakes confirmed by experimental studies of the fine structure of their seismograms. A seismic emissional response was recorded of the medium to the action of man-made sources causing excitation of seismic waves during seismic reconnaissance and DSS.
V.V. Guschin and O.V. Pavlenko studied the problem of non-linear crustal parameters determination from observations of microseisms, the coda-wave and the technogenic periodic signals. An analysis of experimental results produces data of the variations of elastic waves velocities caused by the change in the stress state of the Earth's crust; a strong elastic nonlinearity of rocks was also established.
In his paper, S.V. Gol'din treats the problems of seismic tomography by the passing waves and develops a general approach to reconstruction of seismic images on the basis of kinematic characteristics of waves in nonlinear environment, when velocity variations affect the trajectories of seismic rays.
S.Yu Burmin described improvements introduced to the theory and practice of determination of the seismic boundary position by converted waves using the data on travel-time curves of longitudinal and transversal waves in the flat-layered medium.
The implications of studies discussed above, therefore, indicate that the characteristic feature of this Session and, apparently, of the present-day trend in both theoretical and experimental seismology is focused on the development of physical models, on the synthesis of theory and experiment, on the expansion of models into the region of energy-saturated and nonlinear media, on the application of numerical modeling.
Within the frame of "Seismicity and Active Tectonics" investigation trend, four requested papers, ten scientific communications and 13 poster papers were presented. On the whole, the materials of the session showed a systematic approach to the study, at different scale levels, i.e., global, regional and local, of the hierarchic deep structure of the Earth's crust and the entire lithosphere and of the geodynamic and seismic processes. The main results and problems under discussion were: (a) the structure and dynamics of the geological medium, (b) the structure of seismicity and zonation of seismic hazards, (c) the genesis of earthquake sources and their geological-geophysical manifestations.
D.V. Rundkvist and V.I.Keilis-Borok presented their studies of the peculiarities of deep (and discordant) geostructures, controlling the mantle magmatism, metallogeny and seismicity, carried out on the basis of integration of seismological, geological-geophysical and geodynamic observations and numerical mathematical modeling.
The high-resolution vibroseismic sounding approach seems rather promising in the study of the inner structure of the Earth and for tracing the fine space-time variations of the stress state of the medium in the focal zones of pending and occurring earthquakes. This method was applied to elaborate a concept of a system of active monitoring of seismically prone zones by using powerful low-frequency vibrators, the area registration, and remote data collection.
P.G. Dyad'kov presented a paper describing a complex of theoretical and experimental studies carried out on the Baikal test-area that demonstrate a high variability of the stress field in the Earth's crust by both global and regional factors.
The vast territory of Northern Eurasia, the structural and dynamic peculiarities of which enable to place it in the rank of a planetary seismodynamic system, is now an object of study of its regional structure of seismicity and seismic regime with the aim of its seismic zonation. On this territory, all the main types of lithospheric plates interactions are represented: rift structures, subduction zones, collisions, and transform faults. The studies are based on the concepts of the structural-dynamic and energetic unity of the geophysical medium and the seismogeodynamic processes developing in it, which is clearly evident in the hierarchic orderliness of seismoactive structures and in the trend of their geodynamic development. One of the assets of the new studies conducted for the general seismic zoning (GSZ-97) of Northern Eurasia, as reported by V.I. Ulomov, E.A. Rogozhin, G.I. Reisner, and A.A. Gusev, in parallel with the elaboration of the integral methodology and up-to-date technology, was the construction for the entire territory under consideration of a unified lineament-domaine-focal (LDF) model of the zones of the appearance of earthquake sources (AES), which shows prognostic seismicity in its three-dimensional representation. It is for the first time that the concepts of long earthquake sources and non-linear manifestation of seismogeodynamic processes were used in modeling and calculations, as also the probability and probability-determinate characteristics, which account for both the casual and the regular factors of seismogenesis as well as the different kinds of ambiguities in the initial and output data.
Of particular importance are the identification of seismic sources, the determination of their kinematic and dynamic parameters, the geometric dimensions and recurrence period of earthquakes in these sources. By using independent methods (lattice models, the fractal analysis, recovery of paleoseismodislocations, etc.) it was shown, among other factors, that the earthquake foci are stable structural objects and most often appear in the same locations, whereas the seismic movements in them recur, on the average, with the same periodicity regardless of the earthquake magnitude, but caused by seismotectonic and seismogeodynamic conditions in the region. The identification of potential earthquake foci is carried out by applying the method of identification of seismotectonic characteristics analogous to those in which strong earthquakes were recorded and by applying the analysis of the predominant inter-epicentral distances between the earthquake sources with fixed magnitudes.
Further development of fundamental and applied research in seismotectonics and seismogeodynamics and the identification of potential earthquake sources and seismic zonation should be aimed at forming the scientific principles and methods based on the study of seismicity dynamics, migration of deformation waves and seismic activation, recurrence of earthquakes in the same source and elaboration of other as yet unstudied problems of seismogenesis.
In the course of the "Physics of the Source and Earthquake Prediction" session, four scientific papers, ten oral reports and 25 poster papers were presented.
The emphasis was on the results of modeling earthquake sources in the laboratory and the multidisciplinary study of precursors, on the analysis of the deterministic and statistical approach to prognosis.
In his report, V.S. Kuksenko revealed the essence of the physico-mechanical model of earthquake preparation and demonstrated the general regularities and peculiarities in the process of rock destruction at different levels of the scale. It was demonstrated that a number of prognostic features, derived from the kinetic conception of durability of solid bodies, can be used successfully for prediction of mining shocks, and their further elaboration shows considerable prospects for earthquake prediction.
A.A. Malovichko presented evidence of the reality of this approach for prediction of mining shocks by the example of the Solikamsk mine.
A.V. Ponomarev presented a detailed report on the modeling of the earthquake source development in the unit of high-pressure apparatus.
G.A.Sobolev described how the stages of the earthquake source evolution, observed in the course of modeling in the laboratory, can be used for earthquake prediction. The RTL prognostic algorithm was elaborated. Two scientific predictions of earthquakes in Kamchatka, with magnitude 7 and higher, were obtained in real time by establishing the consecutive stages of weak earthquakes foci clustering, of seismic quiescence and foreshock activation.
The applicability of this algorithm for other geotectonic conditions was confirmed by prognostic studies carried out by Yu.S. Tyupkin and R. Di Giovambattista in Italy.
In his communication A.D. Zavyalov showed that, as revealed in the course of laboratory experiments, the process towards macrofracture is manifested in the seismoactive region as the migration of hypocentres of relatively weak earthquakes towards the source of a stronger pending seismic event.
A number of communications were dedicated to the study of Earth tides variations as earthquake precursors. The problems of nonlinearity of properties of precursors were also discussed.
A.S. Alekseev launched a new concept of multidisciplinary prediction of earthquakes. The solution of the model theoretical problem of deformation field of an earthquake source resulted in the conclusion that vast areas of dilatancy in the near-surface crustal layers can appear. This circumstance provides means to use different geophysical approaches to find precursors associated with the development of the fissuring process.
V.G. Kosobokov discussed the experience of prediction in real time by using the M8 and SM algorithms. It was shown, among other things, that the verification scheme for checking the methods of mid-term earhquakes prediction, suggested in 1991, allowed to confirm the statistical significance of the complex of parameters used in the M8 algorithm.
Sobolev G.A., Chairman, Corresponding Member RAS
Alekseev A.S., Academician
Gol'din S.V., Academician
Keilis-Borok V.I., Academician
Kuksenko V.S., Prof..
Levin B.V., Prof.
Nikolaev A.V., Corresponding Member RAS
Rogozhin E.A., Prof.
Rundkvist D.V., Academician
Rykunov L.N., Corresponding Member RAS
Solov'ev A.A., Prof.
Tyupkin Yu.S., Prof., Scientific Secretary
Ulomov V.I., Prof.
Yanovskaya T.B., Dr.