Geologiya I Geofizzika, 2001, V 42, N 10.
SPECIAL ISSUE:
"International Workshop "Geodynamics of the Tien Shan"
PREFACE
1433
REGIONAL GEOLOGY
GEODYNAMIC EVOLUTION OF THE TIEN SHAN LITHOSPHERE
A. B. Bakirov and R. A. Maksumova
1435
In recent two decades, new data on the age of strata and their spatial
arrangement and geodynamic formation conditions have appeared, which give new
insight into the geologic history of the Tien Shan. This mountain system evolved
in several large megastages and stages, from the Archean through the Quaternary,
which are recognized according to the predominant oceanic or continental regime
of development. The fold-nappe structure of the Tien Shan is the result of
crushing of the edge of the ancient supercontinent into a series of small
blocks, which were then localized on the periphery of the Paleoasian ocean and
underwent accretion, completed in the late Late Paleozoic.
The modern Eurasian plate within Central Asia is separated into several
blocks, whose counter and rotational movements determine the recent geodynamics
of the region. The Tien Shan lithosphere is layered as a result of the
appearance of a migma layer in its lower part, which causes a relatively free
transfer and deformation of its upper part.
Rifting, subduction, accretion, migma, wave guide, asthenosphere, Tien Shan
STRUCTURE AND EVOLUTION OF THE TIEN SHAN NAPPE-FOLDED OROGEN
R. A. Maksumova, A. V. Dzhenchuraeva, and A. V. Berezanskii
1444
New data on stratigraphy , tectonics, and magmatism of the Tien Shan
ancient rocks suggest the plate-tectonic interpretation of the structure and
evolution of the Tien Shan nappe-folded orogen. A new scheme of tectonic
regionalization has been proposed for the Kyrgyz Tien Shan. Emphasis is placed
on recognition of geodynamic complexes (continents, microcontinents, passive and
active margins, open ocean basins, and marginal seas) and structural elements
(autochthons, para-autochthons, allochthons, and neoautochthons), governing the
spatial arrangement of their units with specific texture and composition. Over
the long geologic history of the territory, the continental blocks changed their
outlines, and ocean basins appeared and disappeared. The Caledonian and
Hercynian orogenies in the Tien Shan underwent a complete Wilson cycle. The
Mesozoic history was controlled by within-plate processes of sedimentation and
magmatism. Since the Oligocene, the Tien Shan territory has been involved in the
recent orogeny.
Continent, ocean, passive and active margins, island arcs, marginal sea, volcanic belt
ANALOGS OF THE SINIAN COMPLEX IN THE CENTRAL AND NORTHERN TIEN SHAN
V. V. Kiselev
1453
This paper considers the composition, structure, spatial location, and
paleotectonic formation conditions of Precambrian rocks of the Tien Shan and
adjacent regions analogous to the Sinian series in China and the Tamian(??)-
Vendian strata of the cover of the Russian Platform. A model is proposed for the
Precambrian evolution of the Central Asian ocean basin with pre-Sinian accretion
and Vendian orogeny. The major events are dated: subduction and continent-
marginal volcanism - 830 .. 20 Ma BP, pre-Sinian accretion - 700 .. 20 Ma BP,
rifting - 700-650 Ma BP, and orogeny - 650 .. 10 Ma BP.
Sinian system, Vendian system, Riphean, paleocontinents, Central Asian
ocean basin, accretion, rifting
DEEP STRUCTURE OF THE TURKESTAN PALEOOCEAN SUTURE NORTHEASTERN FERGANA)
O. M. Lesik and A. V. Mikolaichuk
1464
The types and subtypes of a density section of the Earth's crust in the
zone limited by the Talas-Fergana and East Fergana faults are considered. The
zone has an inversion deconsolidated layer in the lower crust (35-50 km). Rock
densities are calculated by an empirical formula with the use of seismic
tomography data on P- and S-wave velocities. In the geological aspect this
territory is remarkable as it involves the South Tien Shan ophiolite belt
notching a suture which resulted from the closure of Turkestan paleoocean in the
Middle Carboniferous. In the Earth's crust section the suture is traceable to a
depth of 15-20 km, is cone-shaped, and is characterized by an increased density
of rocks. Analysis of the gravimetric field and density sections suggests that
within this cone the Earth's crust is saturated with rocks of ophiolite
association.
Inversion layers, density of rocks, Turkestan paleoocean, suture
PETROCHEMICAL FEATURES OF MAGMATITES AND MAJOR KINEMATIC PARAMETERS OF MIDDLE
CARBONIFEROUS-EARLY PERMIAN SUBDUCTION OF THE TURKESTAN PALEOOCEAN (TIEN SHAN,
NORTHERN FERGANA)
K. V. Seliverstov and M. D. Ges'
1471
The paper presents the dip angles of a seismofocal zone, the rate of
underthrust, and other kinematic parameters of Middle Carboniferous-Early
Permian subduction in northern Fergana, reconstructed from the petrochemical
features of coeval magmatites. Comparison of these parameters with those in
zones on some modern active continental margins suggests the metallogenic
similarity of these regions.
Magmatites, petrochemical zonation, subduction, kinematic parameters,
Turkestan paleoocean, Tien Shan
TRANSREGIONAL DEEP FAULTS IN THE TIEN SHAN AS A STRUCTURAL CONTROL
OF LARGE MINERAL DEPOSITS
R. D. Dzhenchuraeva
1476
The paper presents new data on several ore fields and mineral deposits of
the Tien Shan spatially associated with transregional NW faults, which are
easily identified by geophysical methods as they are marked by epicenters of
shallow earthquakes and their aftershocks and abnormal heat flux (up to 130
mW/m2). The faults inherit the strike of older faults and cross structures of
the "Tien Shan" orientation.
In a low-seismisity block east of the Talas-Fergana fault (east of 74°E),
MT soundings reveal a continuous crustal conductor, and the behavior of P waves
indicates the presence of waveguides. The block involves the Barskoon zone of
deep faults and a number of rift depressions. A large gold deposit (Kumtor)
occurs at the intersection of the Borskoon fault with the Mid Tien Shan back-arc
magmatic belt and the "Nikolaev line".
Transregional faults, earthquake epicenters, carbonaceous shales, Kumtor
gold deposit, deep structural control, Moho
GEOPHYSICS
THE SOUTH BAIKAL GEODYNAMIC TESTING GROUND: STRATEGY OF
EARTHQUAKE PREDICTION
S. V. Gol'din, P. G. Dyad'kov, and Yu. A. Dashevskii
1484
A new conceptual approach has been proposed and substantiated for solving
the problem of earthquake prediction and organization of monitoring on the South
Baikal geodynamic testing ground. The new concept takes into account first of
all general geodynamic factors leading to the appearance of foci of metastable
state in the Earth's crust. It has been shown that of great importance are
regional variations in the stress state caused by the processes of
redistribution of crustal stresses during seismic activity in the region as well
as by more distant seismogeodynamic processes on interplate boundaries. It is
supposed that with time the physics of a focus should give way to the physics of
sufficiently large focal zones. One of the main factors determining the seismic
properties of a medium is its block structure. Hence, both experimental and
theoretical studies are necessary to clear up the behavior of dynamic processes
in such block geosystems.
Monitoring, earthquake prediction, seismicity, physics of focus, Baikal
Rift Zone
THICKENING OF MANTLE LITHOSPHERE BENEATH NEW ZEALAND AND THE
ROLE OF BUOYANT CRUST IN THIS PROCESS
P. Molnar, T. Stern, and G. A. Houseman
1497
P-wave delays recorded by two linear arrays of seismographs across the Southern Alps of New Zealand require a high-speed zone in the upper mantle
beneath the Alps. The pattern of residuals does not match that predicted for
subduction of one plate of mantle lithosphere beneath the other. Instead, the
high-speed zone seems to mark a blob of cold lithospheric mantle sinking beneath
the eastern part of the Southern Alps, directly beneath the thickest crust, and
hence where mantle lithosphere has thickened by pure shear. Calculations of
Rayleigh-Taylor instability for a thickening heavy layer buoyed up by a lighter
layer show that the form of the sinking blobs of dense material depends strongly
on the ratio of effective viscosities of crust and mantle. Where the effective
viscosity of the buoyant upper layer (crust) is large, a single blob sinks
beneath the area of maximum thickening of the upper layer. In New Zealand, where
a single sinking blob is inferred, large-strike-slip shear of the region may
have lowered the viscosity of the mantle. Elsewhere, if the viscosity of the
upper layer is small, however, two sinking blobs can form adjacent to the area
where the more buoyant layer (crust) is shortened horizontally. Between the
blobs, the unstable layer (lithospheric mantle) thins. Such a process may occur
within the Tien Shan.
Subduction, mantle lithosphere, Earth's crust, New Zealand
VARIATIONS IN GLOBAL AND MIRROR COMPONENTS OF THE EARTH'S
SEISMIC ACTIVITY
A. M. Fridman, S. K. Tatevyan, Yu. A. Trapeznikov, and A. V. Klimenko
1504
On the basis of harmonic analysis of the data for 125 thousand earthquakes
from the catalog of the National Earthquake Information Center of the U.S.
Geological Survey for the period 1964-90 and of a series of time-dependent
changes of the Earth's angular velocity <$EOMEGA (t)> during the same period,
significant positive correlation has been established between graphs of |<$Ed
OMEGA "/" dt>| and <$EN Bar (t)>, an annual number N(t) of earthquakes for
different regions of the Earth averaged over several years depending on their
hypocenter depths (so-called T-component of seismic activity). Besides, special
attention was paid to studies of spreading and subduction zones. At the same
time, in any two adjacent areas along the both sides of the tectonic plate (in
subduction zones and in the system of mid-ocean ridges and continental mountain
ranges) the correlation coefficient between the functions [<$EN sub 1 (t)^-^N
Bar sub 1 (t)>] and [<$EN sub 2 (t)^-^N Bar sub 2 (t)>], describing the so-
called M-component of seismic activity, is negative. Such behavior is displayed
by shallow (<<400 km) earthquakes.
Sesmicity, earthquake, magnitude, correlation
DEEP-LEVEL HEAT FLOW STUDIES IN THE TIEN SHAN: ADVANCES AND DRAWBACKS
A. D. Duchkov, Yu. G. Shvartsman, and L. S. Sokolova
1516
The paper contains a summary of heat flow studies in the Tien Shan since
the early 1960s and the "Catalog of heat flow determinations in the Tien Shan
and adjacent territories" published for the first time. Heat flow in the region
varies in a broad range from 16 to 134 mW/m2 with the average of 50 _ 12 mW/m2.
The area of enhanced heat flow (>>60 mW/m2) occupies 60 % of the Kyrgyzstan
territory, mostly its northeast and west. The heat flow data have been used for
modeling deep-level (lowermost part of lithosphere) temperatures on the basis
of thermal conductivity equations for the real lithosphere. In the zones of
abnormal heat flow, temperatures on the Moho exceed 1000-1200°C, and the
lithosphere is thinned to 50 km. More detailed and reliable information can be
gained by further geothermal studies in the region using nontraditional methods,
such as gas geochemistry (contents of SiO2 and stable helium isotopes (3He/4He)
in springs) and thermobarometry of crustal and mantle xenoliths.
Heat flow, deep-level temperatures, thermal lithosphere, Tien Shan,
Kyrgyzstan
MANIFESTATION OF THE TIBET PLUME STRUCTURE AND SEISMICITY OF HIGH
ASIA IN REGIONAL GEOPHYSICAL FIELDS
V. N. Pogrebnoi and T. M. Sabitova
1532
This paper present results of a comprehensive analysis of the geophysical
fields in High Asia, which show the peculiarites of the tectonic structure of
the region and geodynamic processes occurring there. Comparison of maps of
geophysical fields, namely, geoidal undulations, anomalous magnetic and gravity
fields, heat flow, shear-wave attenuation, distributions of group velocities of
Rayleigh waves for periods of 10-70 s, and distribution of Pn-wave velocities in
the upper mantle of High Asia, shows that they are all caused by an anomalous
body which might consist of deconsolidated and hot material and is called by us
as the Tibetan plume. We suggest its III-level structure. Comparison of
seismicity and geophysical fields shows a particular correlation between the
occurrence of earthquakes and the structure of geophysical fields. Gradients of
geophysical fields have been found to be indicators of possible zones of strong
earthquakes. Dynamic processes in High Asia are governed by combination of
collision between the Indostan and Euroasian litospheric plates and the ongoing
development of the Tibet plume.
Plume, geophysical fields, seismicity, seismic tomography, deep structure,
mantle diapirism, collision of litospheric plates, geodynamics
SEISMIC TOMOGRAPHY STUDY OF THE TIEN SHAN CRUST
T. M. Sabitova and A. A. Adamova
1543
This paper presents the characteristics of the first 3D velocity model of
the Tien Shan crust, inferred from the traveltimes of P- and S-waves from local
and regional earthquakes, recorded by seismic stations in Kyrgyzstan and
adjacent regions. Seismic tomography imaging provided new data on the deep
structure of the Tien Shan orogen.
Velocity section along the profile crossing source zones of five strong
earthquakes (M>6) shows different structural types of the crust. We describe the
peculiarities of the velocity structure of strong-earthquake zones and criteria
for their distinguishing: waveguides, subvertical weakened ?channels?, and high-
velocity bodies to which the foci of strong events are confined.
We also give examples of geological and geophysical interpretation of the
first velocity model and show its weakness. The necessity of new imaging is
shown. For this purpose a data set was enlarged and described in detail. The
principles of collection of data and calculation of a new model are also
considered. Much attention was paid to calculation of a 1D model which is the
basis for further computation of the new 3D model. Some preliminary results of
3D inversion for P-wave velocities are presented. We believe that the new model,
describing the velocity structure of the Tien Shan in regional scale, will
provide a more argued judgment about the geodynamic processes there.
Seismic tomography, orogen, waveguide, geodynamics
CONSTRAINTS ON THE CRUST AND UPPER MANTLE OF THE KYRGYZ TIEN
SHAN FROM THE PRELIMINARY ANALYSIS OF GHENGIS BROAD-BAND SEISMIC DATA .
S. Roecker
1554
The Tien Shan is the best example of active intracontinental mountain
building in the world. In order to determine how strain has accumulated in the
range, a 28 station network was deployed in the Tien Shan during 1998-2000.
Preliminary analysis of seismograms from this network showed two important
results: first, P-SVwave conversions from the Moho reveal that the crust beneath
the central Tien Shan is unusually thin, being no thicker than that beneath the
Kazakh Shield to the north or the Tarim Basin to the south. Second, splitting of
SKS-waves shows that the strain in the mantle is largely a passive response to
north-south shortening and that this strain is imprinted on the mantle far to
the north of the orogeny itself.
Earth's crust, seismic activity, GPS measurements, geodynamics
MAGNETOTELLURIC AND MAGNETOVARIATIONAL STUDIES OF THE KYRGYZ TIEN SHAN ..
A. K. Rybin, V. Yu. Batalev, P. V. Il'ichev, and G. G. Shchelochkov
1566
Normalized bimodal interpretation of magnetotelluric sounding in the Kyrgyz Tien
Shan mountains provides a reliable geoelectric model for this seismic region.
The model contains a conductive layer in the lower crust and subvertical
conductive zones in the upper crust. High overall conductivity of crustal zones
clearly correlates with low-density zones.
Correction, bimodal interpretation, magnetotelluric sounding, 2D-inversion,
overall conductivity, impedance tensor
GEOPHYSICAL STUDIES OF THE STRUCTURE AND GEODYNAMICS OF A LANDSLIDE
SLOPE IN THE SUUSAMYR RIVER VALLEY (NORTHERN TIEN SHAN, KYRGYZSTAN)
Yu. I. Kolesnikov, S. M. Babushkin, A. D. Duchkov, A. F. Emanov,
V. S. Seleznev, V. M. Solov'ev, and G. M. Trigubovich
1574
The paper presents results of microseismic and electromagnetic studies of a
landslide in the Suusamyr River valley (northern Tien Shan, Kyrgyzstan) and
laboratory pulse transmission experiments on ground samples from the landslide.
Spectral and polarization patterns of microseisms on the slope show that the
main portion of seismic energy in the frequency range of 120 to 210 Hz is
related to microfaulting in zones of stress concentration. The high-resolution
image of the landslide obtained by the applied techniques of areal TEM soundings
and the high sensitivity of seismic parameters to the stress-strain state of the
ground demonstrated in the pulse transmission experiments confirm the efficiency
of geophysical methods in investigation of landslides and slope stability.
Landslide, microseisms, polarization, TEM soundings, pulse transmission
measurements, Tien Shan
MODERN GEODYNAMICS OF THE TIEN SHAN
ORIGIN, DIRECTION, AND RATE OF MODERN COMPRESSION OF THE CENTRAL
TIEN SHAN, KYRGYZSTAN
K. E. Abdrakhmatov, R. Weldon, S. Thompson, D. Burbank, Ch. Rubin,
M. Miller, and P. Molnar
1585
We have determined slip rates on the most active reverse faults,
reconstructed an extensive preorogenic erosion surface, constructed local and
regional cross sections, and dated syntectonic Tertiary sedimentary rocks by
magnetostratigraphy along a north-south transect that spans the Kyrgyz portion
of the west-central Tien Shan. The cumulative Late Quaternary shortening rate
along this transect is ~12 mm/yr. The trabsect consists of five major fault
zones, and the most active faults lie in the interior of the range. Using
geometric models developed in other regions of basement-involved determination,
we estimate shortening during the Late Cenozoic at 40-80 km. Apparent
simultaneous onset of sedimentary basins (at least 3 major basins) about 12 Ma
BP is interpreted to mark the onset of the current orogeny. Given the current
shortening rate of about 10 mm/yr, measured across active faults and by GPS, we
infer that the rate increased with time. We assumed accelerated shortening and
have shown that it has always been of similar style, dominated by north-south
shortening across east-west trending basement-involved reverse faults.
Deformations were localized in five zones, which border the largest and deepest
Tertiary basins, show the greatest structural relief, and contain the currently
most active faults.
Tectonics, orogeny, Central Tien Shan
QUALITATIVE BEARING OF MODERN MOVEMENTS ON THE DEEP GEOELECTRIC
STRUCTURE OF THE EARTH'S CRUST IN THE CENTRAL TIEN SHAN AND
DISTRIBUTION OF SEISMICITY
V. D. Bragin, V. Yu. Batalev, A. B. Zubovich, A. N. Lobanchenko,
A. K. Rybin, Yu. A. Trapeznikov, and G. G. Shchelochkov
1610
Earlier investigations based on seismological data and results of
electromagnetic monitoring of a terrain in one of the most active seismic
regions of the North Tien Shan (Bishkek prognostic test ground) revealed that
regional and local deformations proceed synchronously. It is important to clear
up the mechanism of link of these processes. As known, the seismic process
depends on distribution of stresses in a volume of rocks. The pattern of
distribution of stresses can be statistically mirrored through allocation of
earthquakes in the study terrain. Allocation of seismic events permits us to
judge about the mechanism that controls the distribution of stresses.
The obtained maps of allocation of earthquake epicenters show a stable
maximum in the Hindu Kush area and a gradual decrease in magnitudes at a
distance from it. Preliminary solutions to the model problem on distribution of
stresses in an elastic medium demonstrate that the stresses from a central
source attenuate much faster than it could be inferred from the observed
allocation of earthquakes in the region. It is possible to eliminate this
discrepancy by assuming that horizontal forces act from below.
The GPS data received from 1993 to 1999 on the Tien Shan regional networks
suggest that some tectonic blocks (especially in the eastern part of the study
terrain) move at approximately identical velocities predominantly northward. The
impression is created that the blocks move over the surface of a certain ductile
horizon in the Earth's crust. Magnetotelluric investigations have revealed an
electroconductive horizon in the lower crust throughout South Kazakhstan and the
Tien Shan. This geological bed can be just that plastic horizon, on the top of
which the Earth's crust moves and through which the horizontal forces are
transmitted simultaneously to the entire region at the expense of viscosity of
current matter.
It is established that local seismogenic zones coincide with subhorizontal
areas of elevated conductivity. These areas are tectonic zones of weakening.
Their elevated conductivity is, most likely, caused by inflow of hot solutions
from lower-crust horizon through subvertical zones connecting these horizons.
The subvertical zones are also channels through which seismogenic zones and
lower-crust horizon are interacted by force.
Seismicity, electromagnetic monitoring, plastic horizon, Tien Shan
THE CURRENT DISTRIBUTION OF DEFORMATION IN THE WESTERN TIEN SHAN
FROM BLOCK MODELS CONSTRAINED BY GEODETIC DATA
B. J. Meade and B. H. Hager
1622
We interpret Global Positioning System measurements of interseismic
deformation throughout the western Tien Shan in the context of a block model
which accounts for important geologic features (faults) and physical processes
(elastic strain accumulation.) Through this analysis we are able to quantify the
amount of deformation localized on active structures. In the central part of the
belt the Dzhuanaryk fault zone appears to be the most important thrust fault,
accommodating nearly five millimeters per year of north-south shortening across
it. Conversely, the most widely recognized strike-slip fault in the region, the
Talas-Fergana, is found to have very little of the previously estimated right
lateral motion.
Deformations, GPS measurements, rate fields, geodetic data
DEFORMATION FIELD, EARTH'S CRUST DEEP STRUCTURE, AND SPATIAL
SEISMICITY DISTRIBUTION IN THE TIEN SHAN
A. V. Zubovich, Yu. A. Trapeznikov, B. D. Bragin, O. I. Mosienko,
G. G. Shchelochkov, A. K. Rybin, and V. Yu. Batalev
1634
High density of GPS network in the Tien Shan and long period of
observations have allowed us to construct a velocity vector field of movement on
the Earth's surface and a strain rate field. A compact uniform area of
compressing deformations has been detected. Comparison of the strain rate field
with the spatial distribution of weak seismicity for the same period of time
showed their considerable correlation. The GPS and seismic data were also
compared with data of the magnetotelluric sounding and in particular with
geometry of the surface of a crustal conductive layer detected beneath the Tien
Shan. The area of maximum compressing deformations coincided with the northern
slope of the layer surface, and the strain rate intensity is correlated with the
slope angle magnitude of that surface. Nearly all seismic events occur above the
surface of the crustal conductive layer. The coincidences suggest that the
deformation field and the seismicity distribution are connected by a single
tectonic process and depend on the geometry of the crustal layer.
GPS, velocity field, space geodesy, deformation, seismicity distribution,
magnetotelluric sounding, Tien Shan
THE EFFECT OF ELECTROMAGNETIC IMPACTS ON SEISMICITY OVER THE
BISHKEK GEODYNAMIC TEST GROUND
N. T. Tarasov, N. V. Tarasova, A. A. Avagimov, and V. A. Zeigarnik
1641
The effect of high-power electromagnetic pulses of MHD-generator on the
seismicity of the Bishkek geodynamic test ground has been studied. Local
earthquakes became more frequent after the MHD-generator had been started up.
High activity of local earthquakes was observed 2 to 4 days after startups. It
is shown that electromagnetic pulses cause release of the energy accumulated
during tectonic deformation process. The energy releases as a series of
relatively weak earthquakes rather than as a catastrophic event.
Seismicity, electromagnetic impact, energetic class K, catalogue,
electrokinetics, fluid-containing medium
LONG-TERM AND TIDAL STRAINS RECORDED BY EXTENSOMETERS AND
TILTMETERS (TIEN SHAN - ALA-ARCHA OBSERVATORY)
V. Yu. Timofeev, V. S. Yakovenko, A. D. Duchkov, E. A. Revtova, and B. Ducarme
1650
Measurements performed by means of tiltmeters and expansometers in special-
purpose underground observatories are important part of the research of the
crustal kinematic parameters in the northern Tien Shan. Long runs of tilts and
deformations observed at the Ala-Archa underground station (42.63° N, 74.50° E)
have been analyzed. Results of tidal analysis are reported. Slow variations in tilts and deformations reveal seasonal changes and slope effects caused by
seismic activity of the region. The annual average rate of meridional
compression was <$E3 cdot 10 sup -7> for the period 1985-97 and <$E7 cdot 10 sup
-7> for 1989-97.
Tiltmetry, extensometry, geophysical monitoring, Ala-Archa observatory,
Tien Shan, Kyrgyzstan
MONITORING OF DEFORMATION PROCESSES ON THE ALMATY PROGNOSTIC
TEST GROUND BY TILTMETERS AND EXTENSOMETERS
A. V. Tikhomirov, A. L. Smirnov, I. D. Pil'guk, and M. P. Bakulina
1659
This paper deals with deformation processes in the Earth's crust recorded
by tiltmeters and extensometers in the Northern Tien Shan. The characteristics
of instrumentation are reported. The deformation stations located in different geological conditions are described, and the accuracy of measurements of
deformations is estimated. Examples of deformation disturbances preceding an
earthquake are given. The deformations are of seasonal character. Thus, expansion deformations are recorded in vernal periods, and compressional ones,
in the fall. Zones of development of abnormal deformations during preparation of
a seismic event are characterized. Abnormal deformations irrelevant to
earthquakes are recognized, which are usually due to changes of the groundwater
regime.
Deformation, Earth's crust, disturbances, anomaly, earthquake, stress
LANDSLIDES AND SURFACE BREAKS OF THE 1911, MS 8.2 KEMIN
EARTHQUAKE, KYRGYZSTAN
D. Delvaux, K. E. Abdrakhmatov, I. N. Lemzin, and A. L. Strom
1667
The 1911, Ms 8.2 Kemin (Kebin) earthquake in the Northern Tien Shan
(Kazakhstan, Kyrgystan) formed a complex system of surface ruptures nearly 190
km long and numerous landslides and rock avalanches up to tens of millions of
cubic meters in volume. Judging from their distribution, six fault segments of
the Kemin-Chilik and the Aksu fault zones with different strikes, dips, and
kinematics have been activated. The Kemin earthquake was one of the strongest
events of a sequence of seismic catastrophes that affected the Kungei and Zaili-
Alatau mountain ranges between 1887 and 1938. The effects of the Kemin
earthquake are well documented in a monograph published soon after the event by
K. I. Bogdanovich. In the frame of a European INCO-COPERNICUS program, the
surface ruptures, landslides, and rockslides associated to this earthquake have
been re-examined in detail. In addition, the large-scale tectonic setting of the
Kemin-Chilik and Aksu fault zones has been re-evaluated, and their segments have
been identified and described. The whole system forms a sinistral
transpressional structure, which controls the formation of the mountain ranges
between the Issyk-Kul depression and the Kazakhstan block. The surface ruptures
of the 1911 earthquake can presently be observed in the field over a total
length of nearly 100 km and generally reactivate longer-term cumulative
paleoseismic fault scarps. The presence of well-expressed paleoseismic fault
scarps and several tremendous ancient landslides in the Chon-Kemin, Chon-Aksu, and Aksu valleys can be considered as evidence for strong prehistoric
earthquakes.
Active faults, landslides, 1911 Kemin earthquake, Tien Shan, Kyrgyzstan
PHYSICAL PROPERTIES OF ROCKS
VIBROELASTICITY, ACOUSTIC-PLASTIC EFFECT, AND ACOUSTIC EMISSION
OF LOADED ROCKS
L. M. Bogomolov, B. Ts. Manzhikov, V. N. Sychev,
Yu. A. Trapeznikov,and G. G. Shchelochkov
1678
The effect of low-amplitude vibrations on the process of rock deformation
at a constant load has been studied. Deformation characteristics, parameters of
regime of acoustic emission (AE), and waveforms of isolated AE-pulses have been
recorded during axial compression test of granite samples. A delay of AE
activation after the start of vibration action as well as the aftereffect
following the termination of vibration session have been revealed. The delay
becomes shorter as the load enhances and the time interval between consecutive
vibration sessions decreases. Triggering effect of weak vibrations on the rate
of dilatation rock strain has been found.
The effects observed have been treated in the light of known results
concerning vibroelasticity, acoustic-plastic effect, and acoustic emission of
overburden solids. Suggested theoretical model of vibration action to loaded
geomaterials and scaling effects are considered from the viewpoint of kinetic
concept of solids strength and nonlinear acoustics.
Rock, vobration, plastic strain, constant load, acoustic emission, trigger,
seismicity, scaling factor, kinetics, strength, stick-slip
STRUCTURE OF ACOUSTIC AND ELECTROMAGNETIC EMISSION SIGNALS
ON AXIAL COMPRESSION OF ROCK SPECIMENS
B. Ts. Manzhikov, L. M. Bogomolov, P. V. Il'ichev, and V. N. Sychev
1690
Study was given to a thin structure of pulses of acoustic and
electromagnetic emission recorded on axial compression of specimens of rocks at
the stage of their dilatantion deformation. Four types of signals have been
distinguished in frequency and duration. It is supposed that the type I signals
account for the formation of detachment fractures; the type II signals, of shear
fractures; and the low-frequency type III signals correspond to vibrations of
constructive elements of the loading device. The type IV signals are referred to
as pulse electromagnetic emission caused by charged dislocations coming to a
grain boundary in minerals with ionic bonds, components of granite.
Acoustic emission, electromagnetic radiation, rock, constant load,
fracture, detachment, shear, dislocation, charge, ionic bond, transient
radiation
PERSONALIA
VYSHEMIRSKII VLADISLAV STANISLAVOVICH (to the 80th birthday)
1697