RUSSIAN JOURNAL OF EARTH SCIENCES VOL. 10, ES4004, doi:10.2205/2007ES000293, 2008
2. Results of Research
2.1. Multifactorial Structural-Tectonic Model of NKM
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Figure 2
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[10] The Nizhnekansky Granitoid Massif is located in Siberia a few dozens of kilometers
to the east of Krasnoyarsk. It protrudes from the north-west to south-east at
approximately 60 km, at an average width of about 30 km (Figure 2). According
to the data of geological-geophysical and structural-geomorphological research,
carried out in the western part of the massif and partly in the enclosing rocks,
3 sites were selected for storing HLRW: "Kamenniy'', "Itatskiy'' and "Yeniseiskiy''
[Anderson et al., 2001].
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Figure 3
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[11] The NKM is an integrate autonomously formed synorogenic batholit. The
morphology of its upper and lower edge, vertical magnitude, location of its stem
root, interactions of phases, character of contacts, linearity, and the most
important - the inner structure of the massif, is a result of self-development
(of cooling down and crystallization of the magma and formation of endokynetic
contraction cracks), and on the other part - a consequence of superposition of
the later tectonic process. The morphology of top edge of HKM is rather
complicated and heterogenous. It appears to be a "mirror'' of its
geodynamic activity. The massif occupies the area of about 2000 km
2, 60 km
long and 23-35 km wide. The structure of the massif's crystal edge is rather
complicated and heterogenous. It is intensively divided by modern erosion
processes. The spread of absolute elevations is around 250 m reaching 500 m
at the maximal elevation mark. For revealing the general pattern of its
structure the relief smoothing operation was applied, accomplished by
subtracting from elevation marks the average magnitude of porous deposits,
comprising about 50 m. As a result the scheme of NKM top edge morphology was
developed, shown in Figure 3 [Belov et al., 2007].
[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
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Figure 4
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[13] The second element of the structural-tectonic model of NKM, reflecting
its modern tectonic activity, is the contemporary relief, revealing fairly well
the recent movements of the crust and its modern tectonic activity. For its
analysis the coefficient of relief dissection intensity ( K id) was used,
calculated by sliding window of a uniform grid 4
4 km as the ratio of maximal and
minimal elevation marks to a unit area. The higher is the velocity of elevation
of the area, the higher is
K id. Figure 4 shows the scheme of relief fracturing,
shown in isolines of coefficient
K id.
[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.
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Figure 5
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[17] To reveal the regional block structure a morphological structural analysis
(scale 1:200,000) (method of A. Orlova) was carried out, providing the
capability to select relief-generating faults and multiple-elevation structural
blocks (Figure 5).
[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].
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Figure 6
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[21] For determining the depths of upper edges of anomalies structural index
value
n = 0.5 was used. Applying the linear pseudo-inversion method 25371
marks of specific points were obtained. After the cluster analysis 16183 points
were detected, forming dense clusters. The depths of these points were
interpolated by a Kreiging method on a iniform grid with 1 km interval. The
obtained points distribution is shown in Figure 6.
[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:
σi = (σ2x + σ2y - σ2x σ2y + 3σ2xy)1/2.
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Figure 7
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[25] The presented expression of stress intensity serves as a measure of the
energy, accumulated in the rock by deformations of specific potential energy of
stress. As a unified criteria of the stress-strain level of local parts of the
Nizhnekansky Granitoid Massif stress intensity
σi, and distribution of the
shear stress component
τxy were used (Figure 7a).
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.

Citation: Belov, S. V., A. D. Gvishiani, E. N. Kamnev, V. N. Morozov, and V. N. Tatarinov (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 Sciences
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