RUSSIAN JOURNAL OF EARTH SCIENCES VOL. 10, ES4004, doi:10.2205/2007ES000293, 2008
Development of complex model of evolution of structural-tectonic blocks of the Earth's crust for choosing storage sites of high level radioactive wasteS. V. Belov1, A. D. Gvishiani1, E. N. Kamnev2, V. N. Morozov1, and V. N. Tatarinov1 1Geophysical Center, Russian Academy of Sciences, Moscow, Russia 2VNIPI Promtechnology, Moscow, RussiaContents
Abstract[1] The results of research aimed at predicting the evolution of structural-tectonic blocks of the Earth's crust for selecting Storage Sites of High Level Radioactive Waste (HLRW). The multifactorial structural-tectonic model of Nizhnekansky Granitoid Massif (NKM) was developed, as the most probable burial site of HLRW in Russia. The synthesis of methods of analysis of geological-geophysical data, paleotectonic reconstruction of stress and modeling of stress fields expand the area of predicting stability of geological environment thus providing the capability to make a more accurate assessment of its destruction during a long period of radiobiological danger of HLRW. As it was shown, blocks with high level of concentration of intensiveness of stress are potentially hazardous in relation to development of tectonic destruction. 1. Introduction
[3] The algorithm of predicting the tectonic evolution of STB is based on the following objectives [Morozov and Tatarinov, 2006]. [4] 1. Analysis of construction, search of active structural heterogeneities and geomorphological indicators of tectonic activity of the region and development on its basis of a multifactorial structural-tectonic model. [5] 2. Reconstruction of the tectonic history of the region, representation of the dynamics of alterations taking into account the fragmentary heterogeneous distribution of stress-strain properties. [6] 3. Modeling of distribution of strain fields at the present stage and possible trajectories of formation of new tectonic destructions. Zoning of the area according to the degree of its geodynamic stability, prediction of the possible order of destruction of existing STBs. [7] 4. Carrying out observations of the modern movements of Earth's crust using the methods of space geodesy and high accuracy relevelling methods over 5-6 years, revealing the most active sectors, correction of stress-strain state models and models of destruction of the geological environment. [8] 5. Selection of the most stable STB, the stable state of which is guaranteed over 104-105 years, for the construction of an underground research laboratory. [9] The basic models: 1) multifactorial structural-tectonic model; 2) model of geotectonic evolution; 3) model of stress-strain state; 4) model of predicting of stability of STB. 2. Results of Research2.1. Multifactorial Structural-Tectonic Model of NKM
[12] The analysis of this scheme has shown that the top edge consists of approximately equal parts, the eastern half (section 2) is more elevated and has a rather simple flat undulated topography, reflected by the placid disposition of isolines and a small part of sections with sharp gradients of the massif's top contour. The western part (section 1), in comparison to the eastern, is 200-250 m lower and very irregular. Its indention is subordinate to sub-meridional direction, according to which the considerable part of large tectonic faults of the area is developing. These peculiarities of the relief's indention provide the opportunity of indirect estimating of the trends of modern tectonic stress in the area. 2.2. Tectonic Features of Relief
![]() [14] Analysis of the scheme proves that, according to the character of isolines K id, nonconforming to contact, the elevation of NKM is related not merely to the "floating'' granites, but to the more general tendency of vertical uplift, characteristic to the southern part of the Yeniseiskiy Ridge. At that the territory of NKM according to the intensity of its elevation is divided into two parts by the sub-meridional Maliy Itatsky fault. The right part of the massif, located to the east of the Maly Itat river, is characterized by the most intensive elevation ( K id = 200-400). 2.3. Analysis of Block Morphological Structures[15] Selection of tectonic faults by various authors is mainly based on the study of satellite images, geomorphological analysis of the relief and riverbeds. The works by S. V. Belov, V. M. Datsenko, R. M. Lobaskaya, D. V. Lopatin, N. V. Lukina, V. L. Milovidova provide an ambiguous interpretation of the geometry and characterize the modern activity of tectonic faults.[16] The faults and over-faults appear in the form of terraces of the modern relief up to 100-150 m high. In the zones of faults the geniculate displacements of the river drainage system are marked with the amplitude of horizontal displacement up to 100-450 m, from 3-5 to 15-20 km long and 100-300 m wide. Within the Nizhnekansky massif the system of fractures of north-western orientation is the most striking (with azimuth 325-345o). The second by intensity of its manifestation is the system of fractures with strike azimuth 10-35o. The third one is the system - with azimuth 295-315o. The research carried out by the geologists of the "NPO V. Khlopin Radium Institute'' [Anderson et al., 2001] has revealed the zones of dynamic influence of active faults in the northern part of NKM. There in the contact zone the processes of strain, residual ruptures and plastic alterations are revealed. HLRW burial is possible only outside these zones. Their width is directly proportional to a length of active faults. Within the area a ratio of width to length of the fault zones is close to 0.05 in separate cases reaching 0.08-0.1. At the uplifted fault walls the zones of dynamic influence are wider, at down-thrown (passive) - narrower.
[18] It is significant that the morphological-structural analysis has recorded practically all considerably large faults, selected by N. V. Lukina and R. M. Lobatskaya by deciphering aero- and satellite images. Altogether 10 levels of multi-elevation blocks were detected with the difference of hypsometric levels equal to 50 m. Within NKM there are 7 levels in the interval of heights from 580 m to 230 m. They are of a predominantly isometrical form from 2 km to 8 km in transverse. The eastern sector of NKM has the higher hypsometric level, the elevation marks of structural blocks vary from 530 m to 380 m, in the western section they are more subsided, up to 430-280 m. [19] The comparison of positions of sections in the general block morphological structure of the region shows that the most favorable position belongs to area "Kamenniy''. About 70% of its area lies within the contours of one STB with low hypsometric level of 330-280 m. The position of area "Itatskiy'' is less favorable, because it is located within the limits of two adjoining multiple-elevation blocks. The position of "Yeniseiskiy'' area is even less favorable, it is traversed by the Provoberezhny fault and by a series of adjoining inter-block distortions. 2.4. Finding Structural Non-Uniformities and Sign of Tectonic Activity[20] The above-mentioned model of NKM was amplified and corrected on the basis of analysis of geophysical fields. For this purpose the data of aero-magnetic survey (scale 1:200,000) were used. For obtaining data on the massif's structure on the anomaly component of the magnetic field new algorithms of cluster analysis were applied, based on the analysis of location of specific points of the anomalous field, marking a roof and center of anomaly-generating objects. Besides the location of specific points, marking the roof, in many cases location of specific points, related to centers of magnetic masses of selected objects, can be established. Such points mark objects that can be physically identified with porphyritic veins or highly magnetic gneiss as a part of the crystalline base. For determining the position of specific points the methods were used, based on the cluster analysis of equivalent sources, obtained from a local linear pseudo-inversion (the method of Euler deconvolution-MED). For the further analysis the algorithms of cluster analysis RODIN and KRISTALL were used, applying the fuzzy logic principles, elaborated by the scientists of the Institute of Physics of the Earth's department of mathematical geophysics and geoinformatics, headed by A. D. Gvishiani. The work provides its detailed description [Mikhailov et al., 2003].
[22] It has to be mentioned that about 30% of obtained linear zones aren't related to the available geological data of tectonic deformations. It could be: a) zones of strongly magnetized rocks, emerging at the formation of NKM; b) healed zones of jointing, faults and contacts with intrusive bodies; c) tectonic deformations, not detected earlier. Thus, if a decision about selecting an area is taken, anomalies have to be checked by detailed geologic-geophysical exploration works. The cluster analysis also allowed to establish that isometrical STBs of 6-8 km in size prevail in the NKM structure. 2.5. Modeling of Stress-Deformed State[23] The above-mentioned structural-tectonic model lies in the foundation of modeling of the strain-stress state of NKM based on the method of finite elements. For this purpose we used a deflection model of the generalized plane stress state. A layer was selected in the three-dimensional rock massif, whose width is small in comparison to the massif's length. The kinematic boundary data correlate with the grip conditions, not allowing displacements towards the directions, corresponding to the surrounding contour. Selection of the boundary data provides the capability to reveal the clusters of stress intensity related to structural heterogeneities, typical for a geological environment.[24] The stress intensity value is calculated by formula:
2.6. Monitoring Modern Earth Crust Movements by GPS and GLONASS[26] It is obvious that verification and correction of the results of stress-strain state modeling of NKM and its parts can be completed by field observations in holes or underground working. The more rapid method demands using the Earth crust movements data based on the methods of space geodesy. In 2005 within the borders of NKM a geodynamic testing region was established. Figure 7b shows the map of the polygon's main objects. The project envisaged carrying out observations of the five geomorphological sections, different by relief parameters, related to the modern tectonic activity of the region: 1. The Yenisei river valley, 2. Scarp of the Yeniseiskiy range, 3. Saddle between the Yeniseiskiy range scarp and river Kan valley, 4. Valley of the river Kan, 5. South-eastern edge of NKM.[27] On optimizing the location of points of geodynamic network a number of alternative requirements to their location sites was taken into account: absence of forestry, availability of roads, bedrocks, optimal size of basic lines between observation points. However due to the absence of roads in the north-western part of the region the geodynamic network was asymmetrically shifted to the west. In 2006 the processing of first 6 bases was accomplished. The arrows in Figure 7b show the first directions of displacement of separate points. [28] In 2008-2009 the network extension is planned in "Yeniseiskiy'' area, where it would be possible to set up the main points of observations of the basement rock of the most representative structural blocks. In order to exclude the influence of freezing at the control points, exploring shafts or wells up to 5 m deep would be essential. [29] Thus, as a result of the research the technology of predicting stability of geological strata at selecting the HLRW burial sites was developed, tested in the Nizhnekansky Granitoid Massif. For the development of a multifactorial structural-tectonic model and predicting stability of structural-tectonic blocks of the Earth's crust new algorithms of cluster analysis for searching the indicators of modern tectonic activity and structural heterogeneities and finite-element models of stress-strain state of heterogenous block media were suggested. In order to correct the boundary data of stress of models of STB deformations the results of GPS-observations on the Earth crust movements will be used in the future. Acknowledgments[30] This study was supported by the RFBR (grant no. 05-05-64975) and the ISTC (project no. 2764). ReferencesAnderson, E. B., and, et al. (2001), The results of combined geological and geophysical and specialized research in the area of Kamenniy and abutting areas (Nizhnekansky massif), Report on research work of GUP, 12 pp., "NPO V. Khlopin Radium Institute'', St. Petersburg. Belov, S. V., V. N. Morozov, V. N. Tatarinov, E. N. Kamnev, and Y. Hammer (2007), Study of the structure and geodynamic evolution of the Nizhnekansky massif in relation to high-level radioactive waste disposal, Geoekologia, (2), 1. Mikhailov, V. O., A. Galdeano, M. Diament, A. D. Gvishiani, S. Agayan, Sh. Bogoutdinov, E. Graeva, and P. Sailhac (2003), Application of artificial intelligence for Euler solutions clustering, Geophysics, 68, (1), 168. Morozov, V. N., and V. N. Tatarinov (1996), The methods of selecting crustal areas of the Earth for the disposal of ecologically hazardous waste, Geoecology, (6), 109. Morozov, V. N., and V. N. Tatarinov (2006), Tectonic processes development with time in the areas of HLW disposal: From expert assessment to prognosis, Int. Nuclear Energy science and Technology, 2, (1-2), 65. Received 8 October 2007; revised 9 January 2008; accepted 13 April 2008; published 16 May 2008. Keywords: Nizhnekansky granitoid massif, structural-tectonic model, modeling of stress fields, radioactive waste. Index Terms: 8004 Structural Geology: Dynamics and mechanics of faulting; 8011 Structural Geology: Kinematics of crustal and mantle deformation; 8038 Structural Geology: Regional crustal structure; 8110 Tectonophysics: Continental tectonics: general; 8120 Tectonophysics: Dynamics of lithosphere and mantle: general; 8199 Tectonophysics: General or miscellaneous. ![]() Citation: 2008), Development of complex model of evolution of structural-tectonic blocks of the Earth's crust for choosing storage sites of high level radioactive waste, Russ. J. Earth Sci., 10, ES4004, doi:10.2205/2007ES000293. (Copyright 2008 by the Russian Journal of Earth SciencesPowered by TeXWeb (Win32, v.2.0). |