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Russian Geology and Geophysics

2007 year, number 7

1.
SEISMIC STRAIN IN THE ALTAI-SAYAN ACTIVE SEISMIC AREA AND ELEMENTS OF COLLISIONAL GEODYNAMICS

S.V. Gol'din†, O.A. Kuchai
Institute of Petroleum Geology and Geophysics, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
Keywords: Seismic strain; earthquake mechanisms; collision; geodynamics; stress
Pages: 536-557

Abstract >>
Seismic strain estimated from about 900 earthquake mechanisms in the Altai-Sayan area indicates that the area evolves mainly under N-S compression caused by the India-Eurasia collision. Plastic flow in the mountains of the western and central Altai-Sayan area is controlled by convergence of aseismic rigid blocks, including the Dzungarian microplate, the Minusa basin, the Tuva basin, Uvs Nuur and other basins in the region of Great Lakes in Mongolia. Earthquake rupture follows the existing fault pattern. The pattern of rigid blocks and mountain ranges correlates well with upper mantle thermal heterogeneity as imaged by seismic tomography.
Earthquake mechanisms in the presence of plate convergence depend on different factors. Slip geometry depends on focal depth at a given geodynamic regime, and the latter, in terms of the seismic process, is controlled by lateral (W-E) constraint. Reverse-slip earthquakes most often originate at shallow depths in regions of constrained compression, such as the Tien Shan, and strike slip is the dominant mechanism under non-constrained and moderately constrained compression. The direction of slip is governed by the parallel component of convergence and by the fault pattern. In regions of strain shadow, slip occurs mostly on normal planes, and shallow earthquakes have strike-slip mechanisms. The crust in the collisional region is divided into systems of rigid and plastic blocks (rheological structure) and of fault blocks (fault-block structure). The two types of systems coexist and determine the generally similar but specifically different features of local mass transfer.



2.
EVOLUTIONARY NATURE OF STRUCTURE FORMATION IN LITHOSPHERIC MATERIAL: UNIVERSAL PRINCIPLE FOR FRACTALITY OF SOLIDS

P.V. Makarov
Institute of Strength Physics and Materials Science, Siberian Branch of the RAS, 2/1 Akademichesky prosp., Tomsk, 634021, Russia
Keywords: Rocks; solids; evolution; nonlinear system; fractality principle; hierarchic modeling
Pages: 558-574

Abstract >>
Destruction of geomaterials and geomedia material, as well as general brittle and ductile materials, have been treated theoretically and experimentally using the general approach of nonlinear dynamic systems. The process of destruction in loaded solids (inelastic deformation, damage accumulation, fracture) is presented as a space-time evolution of a nonlinear dynamic system, which allows interpreting all deformation and fracture within the limits of a single theory. The space-time hierarchies of nonlinear systems were found out to undergo collective effects and self-organization. The experimental and theoretical studies of the evolution of loaded solids revealed their universal fractality and showed brittle fracture and plastic deformation to be self-similar processes at different scales, for which scaling parameters have been estimated. The evolution of inelastic strain and destruction of solids is modeled numerically in terms of hierarchic systems.



3.
INVERSE SOLUTION TO THE WAVE EQUATION USING THE LAGUERRE TRANSFORM

A.F. Mastryukov, B.G. Mikhailenko
Institute of Computing Mathematics and Mathematical Geophysics, Siberian Branch of the RAS, 6 prosp. Akad. Lavrentieva, Novosibirsk, 630090, Russia
Keywords: Inverse problem; wave equation; Maxwell's equations; electromagnetic waves; conductivity; permittivity; finite-difference method; Laguerre transform; accuracy
Pages: 575-580

Abstract >>
An inverse solution to the 1D wave equation is obtained using the spectral Laguerre transform to find the distribution of wave velocities at some point of the medium. The problem is solved as optimization in which the function of Laguerre harmonics is minimized by the conjugate gradient or Newton's algorithms.
Reported are velocities of a wave defined by a stepwise constant function. The accuracy of the inverse solution for the Laguerre harmonics is investigated against the approximation accuracy in the boundary problem. The accuracy and efficiency of the Laguerre method are compared to those in the Fourier method.



4.
PREHISTORIC EARTHQUAKES AND FAULT SCARPS IN THE BARGUZIN FAULT ZONE ( Baikal Rift system )

A.V. Chipizubov, S.G. Arzhannikov, R.M. Semenov, O.P. Smekalin
Institute of the Earth's Crust, Siberian Branch of the RAS, 128 ul. Lermontova, Irkutsk, 664033, Russia
Keywords: Paleoseismology; multiple fault scarps; dating fault scarps; magnitudes of prehistoric earthquakes; Barguzin fault
Pages: 581-592

Abstract >>
We studied fault scarps produced by prehistoric earthquakes in the Barguzin fault zone and estimated the ages and the magnitudes of the scarp-forming events in each scarp segment from their structure, morphology, and scarp parameters. Morphological and structural data reveal two to four surface-rupturing events with displacement up to 5-9.5 m, and two events showed 14C ages of 4.5 and 9 kyr. The area of the Barguzin Fault may have experienced six 7.5 ≥ M < 8.0 earthquakes and two M ≥ 8.0 (8.0-8.2) events for the past 10-12 kyr.



5.
RELATIONSHIP OF THE SEISMIC ACTIVITY OF THE TUVINIAN AND ADJACENT MONGOLIAN AREAS WITH THE FRACTAL DIMENSIONALITY OF A FAULT SYSTEM

O.D. Ayunovaa, Yu.A. Kalusha, V.M. Loginovb
aTuvinian Institute of Complex Natural Resources Exploration, Siberain Branch of the RAS, 117a ul. Internatsional'naya, Kyzyl, 667007, Russia
bInstitute of Mathematics, Physics and Informatics of Krasnoyarsk State Pedagogical University, 7 ul. Perensona, Krasnoyarsk, 660049, Russia
Keywords: Mathematical simulation; seismic activity; fault system; fractal dimensionality; geoinformatics
Pages: 593-597

Abstract >>
Using GIS technologies, we carried out a complex spatial analysis of the seismic activity and fractal dimensionality of fault fields in the Tuvinian and adjacent Mongolian areas. Results obtained showed that seismic activity is intrinsic to zones with the low fractal dimensionalities (1.2-1.4) of fault systems.



6.
LATE CENOZOIC FAULT PATTERN AND STRESS FIELDS IN THE BARGUZIN RIFT ( Baikal region )

O.V. Lunina, A.S. Gladkov
Institute of the Earth's Crust, Siberian Branch of the RAS, 128 ul. Lermontova, Irkutsk, 664033, Russia
Keywords: Fault; stress field; Late Cenozoic; Barguzin rift; Baikal region
Pages: 598-609

Abstract >>
New structural and tectonophysical data, combined with the published geophysical and seismological evidence, were used to map the Late Cenozoic fault pattern and crustal stress in the Barguzin rift. Faults striking in the NE direction are the most abundant elements of the rift structure. A special part in the Late Cenozoic patterns of faults and stresses belongs to an over 400 km long N-S lineament which shows up as a system of separate fault segments between 110



7.
GRAVITY EFFECTS CAUSED BY MODERATE EARTHQUAKES: ROLE OF LOCAL FAULT PATTERN

O.V. Lunina, Ya.B. Radziminovich, A.S. Gladkov
Institute of the Earth's Crust, Siberian Branch of the RAS, 128 ul. Lermontova, Irkutsk, 664033, Russia
Keywords: Rockfall; fault; earthquake; intensity
Pages: 610-613

Abstract >>
A rockfall was discovered on the left bank of the Verkhnyaya Angara River, 25 km away from the northwestern doorway of the North Muya tunnel of the Baikal-Amur Railway. We investigate the tectonic position of the rockfall and its linkage to a moderate earthquake using structural data and show that earthquakes of this intensity can produce notable ground failure if the local fault pattern is favorable for passage of seismic waves.



8.
THE EFFECT OF SEISMIC EVENTS ON SLIDING DEFORMATIONS OF THE BRATSK WATER RESERVOIR SHORES

Yu.B. Trzhtsinsky, E.A. Kozyreva, Ya.B. Radziminovich
Institute of the Earth's Crust, Siberian Branch of the RAS, 128 ul. Lermontova, Irkutsk, 664033, Russia
Keywords: Natural-engineering system; reservoir; response of geologic environment; dynamics of landslides
Pages: 614-615

Abstract >>
Research has shown that the creation of the Bratsk water reservoir considerably changed the seismic conditions in this area of the Siberian Platform. Seismic records revealed a significant increase in the energy classes of earthquakes with epicenters in the north of the reservoir, in trap intrusion zone. The change in engineering-geologic conditions and frequent seismic events affected the rate of development of gravitational deformations on the shore slopes.



9.
UPPER MANTLE LATERAL INHOMOGENEITY ESTIMATED USING GLOBAL MVS

V.V. Plotkin, A.Yu. Belinskaya, P.A. Gavrysh
Institute of Petroleum Geology and Geophysics, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
Keywords: Upper mantle; global MVS; lateral variations of Earth's electrical conductivity; mantle hot fields; spherical harmonic analysis
Pages: 616-625

Abstract >>
We processed synchronous observatory MVS data at periods from 1.2 to 6 days to estimate lateral conductivity variations in the upper mantle. The inverse problem for depth-dependent conductivity distribution was solved using correlation of the measured surface components of the geomagnetic field. We applied spherical harmonic expansion of the complex amplitudes of time harmonics and multiple averaging of the amplitudes obtained for different SH sets. The chosen approximation approach was tested by comparing the EM field simulated for a smoothly inhomogeneous Earth with the exact forward solution. The SHA-analyzed observatory data for fifteen magnetic storms were used to map global apparent conductivity variations.



10.
A GEOELECTRICAL MODEL OF THE BARGUZIN BASIN IN THE BAIKAL RIFT ZONE

M.I. Epov, N.N. Nevedrova, A.M. Sanchaa
Institute of Petroleum Geology and Geophysics, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
Keywords: Vertical electric soundings; data processing; 2D forward modeling and inversion; Barguzin basin
Pages: 626-641

Abstract >>
We processed data from geophysical survey archives of the 1950s acquired in intermontane basins in the Baikal rift, including a large collection of vertical electric soundings (VES) from the Barguzin basin, which remained only partly interpreted. The processing and reinterpretation became possible with the advanced computing facilities and software for forward modeling and inversion, and GIS tools. We estimated the electrical parameters and modeled the complex block structure of the uppermost basement and sediments beneath the Barguzin basin.