Seismic, Structural and Petrological Models of the Subcrustal Lithosphere in Southern Germany: A Quantitative Revaluation

—Anisotropy in the subcontinental lithosphere becomes increasingly important, because it is observed in many seismic studies especially for P _n -waves. Typical rocks of the uppermost mantle are peridotites, which predominantly exhibit a pronounced elastic anisotropy. This anisotropy is mainly caused by the anisotropic elastic properties and the lattice preferred orientation (here referred to as texture) of olivine. To evaluate the elastic anisotropy of peridotites from the subcontinental lithosphere, specimens of the Northern Hessian Depression (Germany) and the Balmuccia Ultramafic Massif (Northern Italy) have been used. They comprise four olivine texture types, which are characteristic for olivine textures observed worldwide. The bulk rock elastic properties have been calculated using olivine and orthopyroxene textures, their single-crystal elastic constants at ambient pressure/temperature conditions and their volume fraction. Clinopyroxene and spinel are assumed to be randomly distributed. The effect of four different orientations of the foliation within the uppermost mantle has been evaluated, since this orientation is usually unknown.¶Two of the olivine textures have a pronounced azimuthal dependence of compressional waves when a horizontal foliation within the uppermost mantle is presumed. These variations cause significant azimuthal variations of the P-wave reflections coefficients at the Moho. Primarily, we predict a significant azimuthal dependence of the critical points where the reflected amplitude increases from approximately 15% to 95%. Possibly, these azimuthal variations can be detected by seismic reflection measurements carried out at earth surface.¶The remaining two texture types only manifest a small directional dependence. When anisotropy of compressional waves is observed in seismic studies, these latter types can only be of subordinate importance. However, all of the peridotites investigated are able to explain the seismically observed azimuthal variations of compressional waves when a vertical foliation is proposed. This ambiguity can be substantially reduced when shear waves (S-waves) are considered. The directional distribution of S-wave velocities and of the S-wave splitting exhibits characteristic patterns for the different olivine texture types. This could be used to discriminate between different texture types and orientations of the foliation within the uppermost mantle. A fundamental requirement for a more comprehensive interpretation is the availability of detailed S-wave observations. The maximum S-wave splitting in the peridotites investigated coincides with the maximum of the faster (leading) S-wave. This may be of importance to detect S-wave splitting in future seismic studies.     

Composition,temperature, and thickness of the lithosphere of the Archean Kaapvaal craton

A new model is proposed for the structure of the Kaapvaal craton lithosphere. Based on chemical thermodynamics methods, profiles of the chemical composition, temperature, density, and S wave velocities are constructed for depths of 100–300 km. A solid-state zone of lower velocities is discovered on the S velocity profile in the depth interval 150–260 km. The temperature profiles are obtained from absolute values of P and S velocities, taking into account phase transformations, anharmonicity, and anelastic effects. The examination of the sensitivity of seismic models to the chemical composition showed that relatively small variations in the composition of South African xenoliths result in lateral temperature variations of ～200°C. Inversion of some seismic profiles (including IASP91) with a fixed bulk composition of garnet peridotites (the primitive mantle material) leads to a temperature inversion at depths of 200–250 km, which is physically meaningless. It is supposed that the temperature inversion can be removed by gradual fertilization of the mantle with depth. In this case, the craton lithosphere should be stratified in chemical composition. The depleted lithosphere composed by garnet peridotites exists to depths of 175–200 km. The lithospheric material at depths of 200–250 km is enriched in basaltoid components (FeO, Al₂O₃, and CaO) as compared with the material of garnet peridotites but is depleted in the same components as compared with the fertile substance of the underlying primitive mantle. The material composing the craton root at a depth of ～275 km does not differ in its physical and chemical characteristics from the composition of the normal mantle, and this allows one to estimate the thickness of the lithosphere at 275 km. The results of this work are compared with data of seismology, thermal investigations, and thermobarometry.     

利用瑞利面波相速度和方位各向异性研究鄂尔多斯块体的岩石圈变形特征

利用在鄂尔多斯块体内部布设的45个宽频带流动台站和固定台站的资料,用双平面波方法反演了20~143 s共12个周期的基阶瑞利面波的平均相速度和方位各向异性,并反演了一维S波速度结构.反演结果显示50~100 s中长周期的瑞利面波相速度高于AK135速度模型的相速度,为高速异常,S波速度显示高速异常主要位于180 km深度范围内,表明鄂尔多斯块体保留有厚的高速岩石圈.20~111 s周期的方位各向异性强度小于1%,较小的各向异性表明鄂尔多斯块体岩石圈变形较弱.20~50 s周期的平均快波方向为近EW向,67~143 s周期的平均快波方向为NW-SE向,相对发生了整体改变,快波方向的转变约开始于80~100 km深度范围,这表明岩石圈上下部存在着由不同变形机制导致的各向异性.上部岩石圈中各向异性可能主要为残留的“化石”各向异性,而下部岩石圈各向异性可能是现今板块构造运动导致的变形而形成.鄂尔多斯块体岩石圈垂向上的变形差异可能主要与岩石圈温度随深度的变化以及青藏高原NE-NNE向挤压引起的上部岩石圈逆时针旋转有关.     

Age-dependent Large-scale Fabric of the Mantle Lithosphere as Derived from Surface-wave Velocity Anisotropy

—Systematic variations of the seismic radial anisotropy ξ to depths of 200–250 km in North America and Eurasia and their surroundings are related to the age of continental provinces, and typical depth dependences of ξ _R are determined. The relative radial anisotropy ξ _R in the mantle lithosphere of Phanerozoic orogenic belts is characterized by ν _SH > ν _SV , with its maximum depth of about 70 km, on the average, while beneath old shields and platforms, it exhibits a maximum deviation from ACY400 model (Montagner and Anderson, 1989) at depths of about 100 km with ν _SV ≥ν _SH signature. An interpretation of the observed seismic anisotropy by the preferred orientation of olivine crystals results in a model of the mantle lithosphere characterized by anisotropic structures plunging steeply beneath old shields and platforms, compared to less inclined anisotropies beneath Phanerozoic regions. This observation supports the idea derived from petrological and geochemical observations that a mode of continental lithosphere generation may have changed throughout earth's history.     

The model of the depth variations in the properties and state of the rocks in the upper,middle, and lower continental crust of the Kola-Norwegian block,Kola Peninsula

Based on the experimental and calculated data, the model of depth variations in density, as well as the velocities of longitudinal (P) and transverse (S) waves, within the upper, middle, and lower crusts of the Kola-Norwegian block down to a depth of about 40 km is suggested. The variations in density and the velocities of the P- and S-waves are primarily caused by the changes in the mineral composition of the rocks. The relative reduction in the velocities of the P- and S-waves under the action of the increasing pressure and temperature in the depth interval from 5 to 37 km is estimated at ～2%.     

Shear velocity structure of crust and uppermost mantle in China from surface wave tomography using ambient noise and earthquake data

We present a 3D model of shear velocity of crust and upper mantle in China and surrounding regions from surface wave tomography.We combine dispersion measurements from ambient noise correlation and traditional earthquake data.The stations include the China National Seismic Network,global networks,and all the available PASSCAL stations in the region over the years.The combined data sets provide excellent data coverage of the region for surface wave measurements from 8 to 120 s,which are used to invert for 3D shear wave velocity structure of the crust and upper mantle down to about150 km.We also derive new models of the study region for crustal thickness and averaged S velocities for upper,mid,and lower crust and the uppermost mantle.The models provide a fundamental data set for understanding continental dynamics and evolution.The tomography results reveal significant features of crust and upper mantle structure,including major basins,Moho depth variation,mantle velocity contrast between eastern and western North China Craton,widespread low-velocity zone in midcrust in much of the Tibetan Plateau,and clear velocity contrasts of the mantle lithosphere between north and southern Tibet with significant E–W variations.The low velocity structure in the upper mantle under north and eastern TP correlates with surface geological boundaries.A patch of high velocity anomaly is found under the eastern part of the TP,which may indicate intact mantle lithosphere.Mantle lithosphere shows striking systematic change from the western to eastern North China Craton.The Tanlu Fault appears to be a major lithosphere boundary.     

Regional fabric of the deep lithosphere in central Europe from seismic anisotropy

Summary The large scale anisotropic structures with plunging symmetry axes in the subcrustal lithosphere of central Europe were derived from independent observations of teleseismic P-residual spheres and polarizations of the split SKS waves. The dipping structures are interpreted as remnants of palaeo-subduction systems which retain olivine orientations from ancient oceanic lithosphere. Values of k_P and k_S estimated from observed teleseismic P and SKS data are within the range of anisotropies found for the upper mantle rocks. The Variscides of central Europe may thus be characterized by two palaeo-subduction systems, with symmetry axes divergent relative to the suture between the Moldanubicum and Saxothuringicum.     

Velocity properties of the lithosphere in the ocean-continent transition zone in the Kamchatka region from seismic tomography data

Arrival times of P and S waves from local earthquakes in the Kamchatka area of the Kurile-Kamchatka Island Arc are used for calculating a spatial model of the elastic wave velocity distribution to a depth of 200 km. The lithosphere is shown to be strongly stratified in its velocity properties and laterally heterogeneous within the mantle wedge and seismic focal zone. A lower velocity layer (an asthenospheric wedge) is identified at depths of 70–130 km beneath the Eastern Kamchatka volcanic belt. The morphology of the Moho interface and the velocity properties of the crust are studied. The main tectonic structures of the region are shown to be closely interrelated with deep velocity heterogeneities. Regular patterns in the statistics of the earthquakes are analyzed in relation to variations in the elastic wave velocities in the focal layer. A mechanism of lithospheric block displacements along weakened zones of the lower crust and upper mantle is proposed.     

Constraining P-wave velocity variations in the upper mantle beneath Southeast Asia

We have produced a P-wave model of the upper mantle beneath Southeast (SE) Asia from reprocessed short period International Seismological Centre (ISC) P and pP data, short period P data of the Annual Bulletin of Chinese Earthquakes (ABCE), and long period PP-P data. We used 3D sensitivity kernels to combine the datasets, and mantle structure was parameterized with an irregular grid. In the best-sampled region our data resolve structure on scale lengths less than 150 km. The smearing of crustal anomalies to larger depths is reduced by a crustal correction using an a priori 3D model. Our tomographic inversions reveal high-velocity roots beneath the Archean Ordos Plateau, the Sichuan Basin, and other continental blocks in SE Asia. Beneath the Himalayan Block we detect high seismic velocities, which we associate with subduction of Indian lithospheric mantle. This structure is visible above the 410 km discontinuity and may not connect to the remnant of the Neo-Tethys oceanic slab in the lower mantle. Our images suggest that only the southwestern part of the Tibetan plateau is underlain by Indian lithosphere and, thus, that the upper mantle beneath northeastern Tibet is primarily of Asian origin. Our imaging also reveals a large-scale high-velocity structure in the transition zone beneath the Yangtze Craton, which could have been produced in multiple subduction episodes. The low P-wave velocities beneath the Hainan Island are most prominent in the upper mantle and transition zone; they may represent counter flow from the surrounding subduction zones, and may not be unrelated to processes beneath eastern Tibet.     

Modeling of the thermal structure of continental lithosphere

The thermal structure of continental lithosphere (the temperature, heat flows, and heat generation in the crust and lithosphere) is reconstructed from geothermal, seismic, and petrologic data. The first step is the determination of the temperature profile from absolute P and S wave velocities (T _{P, S} ). The T _{P, S} profile is then adjusted to a thermophysical model of conductive transfer. In addition, the surface heat flow and the T _{P, S} profile are used to determine heat generation, thicknesses of crustal layers, and heat flow components in the crust and lithosphere. A feature inherent in the solution of the thermophysical inverse problem obtained in this paper is the use of constraints derived from the temperature reconstruction by seismic data inversion. As a result, the analytical dependence of the temperature on depth, the intensity of radiogenic heat sources in the crust, and heat flow components in the crust and lithosphere are determined.     

Upper mantle low anisotropy channels below the Pacific Plate

A new 3D anisotropic model has been obtained at a global scale by using a massive dataset of seismic surface waves. Though seismic heterogeneities are usually interpreted in terms of heterogeneous temperature field, a large part of lateral variations are also induced by seismic anisotropy of upper mantle minerals. New insight into convection processes can be gained by taking seismic anisotropy into account in the inversion procedure. The model is best resolved in the Pacific Plate, the largest and the most active tectonic plate. Superimposed on the large-scale radial (ξ parameter) and azimuthal anisotropy (of V_SV velocity) within and below the lithosphere, correlated with present or past Pacific Plate motions, are smaller-scale (<1000 km) lateral variations of anisotropy not predicted by plate tectonics. Channels of low anisotropy down to a depth of 200 km (hereafter referred to as LAC) are observed and are the best resolved anomalies: one east-west channel between Easter Island and the Tonga-Kermadec subduction zones (observed on both radial and azimuthal anisotropies) and a second one (only observed on azimuthal anisotropy) extending from the south-west Pacific up to south-east Hawaii, and passing through the Polynesia hotspot group for plate older than about 40 Ma. These features provide strong constraints on the decoupling between the plate and asthenosphere. They are presumably related to cracking within the Pacific Plate and/or to secondary convection below the rigid lithosphere, predicted by numerical and analog experiments. The existence and location of these LACs might be related to the current active volcanoes and hotspots (possibly plumes) in the Central Pacific. LACs, which are dividing the Pacific Plate into smaller units, might indicate a future reorganization of plates with ridge migrations in the Pacific Ocean.     

Subcrustal structure of the black sea basin from seismological data

The P-wave travel time data from the earthquakes offshore and onshore around the Black Sea are used for the tomographic reconstruction of the three-dimensional (3D) velocity distribution in the lithosphere of the region. The preliminary refinement of the foci parameters (the coordinates and origin time) has reduced the random errors in the travel-time data. The earthquake data were supplemented by the previous deep seismic sounding (DSS) data on the profiles in Crimea and offshore off the Black Sea. The dataset included more than 4000 travel times overall. In order to eliminate the crustal effect, the travel times were reduced to a surface at a depth of 35 km corresponding to the mean Moho depth in the region. The improved crustal model was used for removing the contribution of the crust from the initial data. The new tomography method, which was recently developed by one of the authors and which relies on the assumption of smoothness of the lateral velocity variations, was applied for reconstructing the velocity structure of the upper mantle beneath the Black Sea up to a depth of 95 km. The lateral velocity variation maps at different depths and the vertical velocity distributions along the meridional and sublatitudinal cross sections across the Black Sea were constructed. High velocities were revealed in the subcrustal lithosphere, and the structural difference below two subbasins—the West Black Sea (WBS) and the East Black Sea (EBS) ones—was established. It shows that the high-velocity body below the WBS is located deeper than below the EBS and is distinguished by higher velocities. Based on these results, it is concluded that the lithosphere beneath the Black Sea has a continental origin.     

用面波方法研究上扬子克拉通壳幔速度结构

本文研究采用单台法和双台法提取了穿越上扬子的基阶面波相速度和群速度频散;通过对提取的面波群速度和相速度频散进行联合反演,得到的1-D SV速度模型显示上扬子块体下地壳S波速度与典型克拉通区域相当,其上地幔顶部80~170 km深处存在高速的岩石圈盖层,较AK135模型要快2%~3%,其岩石圈厚度约为180 km.在上扬子地区,径向各向异性集中分布在300 km以浅的岩石圈与软流圈部分,其中岩石圈部分SH波比SV波波速要快2%~4%,软流圈部分SH波比SV波波速要快3%~5%;Rayleigh波相速度方位各向异性分析结果显示,上扬子块体周期为25~45 s（大致相当于30~70 km深度范围内）的Rayleigh波相速度存在1.8%~2.7%不等的方位各向异性,其快波方向介于147°~174°.我们认为上扬子块体径向各向异性集中分布在岩石圈、软流圈部分,且各向异性随深度变化, 其岩石圈部分各向异性为大陆克拉通化的遗迹,软流圈部分各向异性与现今板块运动相关.     

Stability of the boundary layer between the lithosphere and convecting mantle and the steady-state lithospheric geotherm

In the steady state, the convective boundary layer (CBL) (the transition from the lithosphere to the convecting mantle, the lithosphere-asthenosphere boundary) is on the verge of stability. This determines its depth, thickness, and the steady-state temperature distribution in the lithosphere. Had the mantle been homogeneous, the base of the lithosphere at the current potential temperature would lie globally at the same depth H _rh of 50 to 70 km. Actually, the regime of interaction of the mantle convection with the lithosphere is determined by the relationship between this depth and the thickness H _depl of the chemical boundary layer including the crust and the layer of the depleted rock. If the thickness of the chemical boundary layer is small H _depl < H _rh, as it is the case in the present-day oceanic mantle, the suboceanic regime is established with the mantle convection that does not reach the base of the chemical boundary layer. In this case, the top of CBL is located at depth H _rh, while the oceanic heat flow and the depth of the seafloor only depend on the potential temperature T _p and, within the areas where the crust is older than 60 to 70 Ma, are the same everywhere far from the disturbed territories (the hot points and the subduction zones). The absence of noticeable distinctions between the heat flow in the different oceanic basins suggests a global constancy of the potential temperature. If H _depl > H _rh, the subcontinental regime of the interaction of the mantle convection with the lithosphere is established. In this case, the CBL is immediately adjacent to the depleted lithosphere, its top is located at depth H _depl, and the surface heat flow q(T _p, H _depl) not only depends on the potential temperature T _p but also on the the thickness of the depleted lithosphere H _depl; it decreases with increasing H _depl and, therefore, with the age of the lithosphere. Given the potential temperature, the dependence q(T _p, H _depl) agrees well with the envelope of the results of kimberlite xenolith thermobarometry presented in the diagram of the deepest xenolith depth as a function of the heat flow. It is likely that in the lowest part of the continental lithosphere there is a zone of horizontal shear deformation, from where kimberlites entrain the strongly deformed and, at the same time, the deepest xenoliths. Besides, the azimuthal anisotropy of seismic velocities can be associated with this zone. The change in its direction with depth can be observed as the Lehmann discontinuity.     

Anisotropic models of the upper mantle

Long period Rayleigh wave and Love wave dispersion data, particularly for oceanic areas, have not been simultaneously satisfied by an isotropic structure. In this paper available phase and group velocity data are inverted by a procedure which includes the effects of transverse anisotropy, anelastic dispersion, sphericity, and gravity. We assume that the surface wave data represents an azimuthal average of actual velocities. Thus, we can treat the mantle as transversely isotropic. The resulting models for average Earth, average ocean, and oceanic regions divided according to the age of the ocean floor, are quite different from previous results which ignore the above effects. The models show a low-velocity zone with age dependent anisotropy and velocities higher than derived in previous surface wave studies. The correspondence between the anisotropy variation with age and a physical model based on flow aligned olivine is suggestive. For most of the Earth SH > SV in the vicinity of the low-velocity zone. Neat the East Pacific Rise, however, SV > SH at depth, consistent with ascending flow. Anisotropy is as important as temperature in causing radial and lateral variations in velocity. The models have a high velocity nearly isotropic layer at the top of the mantle that thickens with age. This layer defines the LID, or seismic lithosphere. In the Pacific, the LID thickens with age to a maximum thickness of ～50 km. This thickness is comparable to the thickness of the elastic lithosphere. The LID thickness is thinner than derived using isotropic or pseudo-isotropic procedures. A new model for average Earth is obtained which includes a thin LID. This model extends the fit of a PREM, type model to shorter period surface waves.     

Thermal structure and thickness of the lithospheric mantle underlying the Siberian Craton from the kraton and kimberlit superlong seismic profiles

A self-consistent approach is proposed for the investigation of the thermal conditions, chemical composition, and internal structure of the upper mantle of the Earth. Using this approach, the thermal state of the lithospheric mantle beneath the Siberian Craton (SC) is reconstructed from P velocities, taking into account the phase transitions, anharmonicity, and the effects of anelasticity. The velocities of seismic waves are more sensitive to temperature than to the composition of the mantle rocks, which allows the velocity models to be effectively used for reconstruction of the thermal regime of the mantle. The temperature at depths 100–300 km is reconstructed by inversion of the Kraton and Kimberlit superlong seismic profiles for compositions of the garnet harzburgite, lherzolite, and intermediate composition of garnet peridotite. The averaged temperature in the normal continental mantle is reconstructed by inversion of the IASP91 reference model for depleted and fertile substance. One-dimensional models and two-dimensional thermal fields undergo a substantial fall in temperature (～300–600°C) beneath the Siberian Craton as compared to the temperatures of the continental mantle and paleotemperatures inferred from the thermobarometry of xenoliths. Temperature profiles of the Siberian Craton deduced from seismic data lie between the conductive geotherms of 32.5–40.0 mW/m² and below the P(H)-T values obtained for low- and high-temperature xenoliths from the Mir, Udachnaya, and Obnazhennaya kimberlite pipes. The thickness of the thermal lithosphere estimated from the intersection with the potential adiabat is 300–320 km, which is consistent with the data on heat flows and seismotomographic observations. This provides grounds for the assumption that the low-temperature anomalies (thermal roots of continents) penetrate down to a depth of 300 km. The analysis of the sensitivity of seismic velocity and density to the variations in temperature, pressure, and chemical and phase composition of petrological models shows that recognition of fine differences in chemical composition of the lithospheric rocks by seismic methods is impossible.     

P-SH Conversions in Layered Media with Hexagonally Symmetric Anisotropy: A CookBook

—Reflectivity synthetic seismograms demonstrate that the type, layering and orientation of 1-D anisotropy influences strongly the coda of teleseismic P waves at periods T > 1 sec, particularly P-SH converted waves. We assume the simplest form of anisotropy described by an elastic tensor with a symmetry axis ? of arbitrary orientation. The resulting phase velocities vary as cos 2ξ with respect to that axis. Using three families of simple crustal models, we compare the effects of an anisotropic surface layer with reverberations caused by both "thick" and "thin" layers of anisotropy at depth. If anisotropy in the surface layer is significant, the polarization of direct P can be distorted to generate a transverse component, followed by Ps and a prominent shear reverberation converted from direct P at the free surface. If the anisotropic layer is buried, the first, and often the most prominent, arrival on the transverse component is the P-to-SH conversion at its upper surface. If the anisotropic layer is sufficiently thin, P-to-SH conversions from its boundaries interfere to form a derivative pulse shape on the transverse component, which could be mistaken as the signature of shear-wave splitting. If ? is horizontal, compressional (P) and shear (S) anisotropy both produce similar waveform perturbations with four-lobed azimuthal patterns, suggesting that a weighted stack of P coda from different back-azimuths would improve signal-to-noise. For ? tilted between the horizontal and vertical, however, the effects of P- and S-anisotropy differ greatly. The influence of P-anisotropy on P-to-S conversion is greatest for a symmetry axis tilted at 45° to the vertical, where its azimuthal pattern has two lobes, rather than four. Combinations of P- and S-anisotropy typically lead to a composite azimuthal dependence in the P-coda reverberations.     

Love-Rayleigh wave incompatibility and possible deep upper mantle anisotropy in the Iberian peninsula

Love and Rayleigh wave phase velocities are analyzed with the goal of retrieving information about the anisotropic structure of the Iberian lithosphere. The cross-correlation method is used to measure the interstation phase velocities between diverse stations of the ILIHA network at periods between 20 and 120 s. Despite the 2-D structure of the network, the Love wave data are too few to enable an analysis of phase velocity azimuthal variations. Azimuthal averages of Love and Rayleigh wave phase velocities are calculated and inverted both in terms of isotropic and anisotropic structures. Realistic isotropic models explain the Rayleigh wave and short-period Love wave phase velocities. Therefore no significant anisotropy needs to be introduced in the crust and down to 100 km depth in the upper mantle to explain our data. A discrepancy is observed only at long periods, where the data are less reliable. Love wave data at periods between 80 and 120 s remain 0.15 km/s faster than predicted by isotropic models explaining the long-period Rayleigh wave data. Possibilities of biases in the measurements due to interferences with higher modes are examined but seem unlikely. A transversely isotropic model with 8% of S-wave velocity anisotropy in the upper mantle at depths larger than 100 km can explain the whole set of data. In terms of a classical model of mantle anisotropy, this corresponds to 100% of the crystals perfectly oriented in the horizontal plane in a pyrolitic mantle. This is a rather extreme model, which predicts at time delay between 0 and 2 seconds for split SKS.     

Velocity and Density Heterogeneities of the Tien-Shan Lithosphere

—The Tien-Shan orogene is a region in which the earth’s crust undergoes considerable thickening and tangential compression. Under these conditions the lithosphere heterogeneities (composi tion, rheological) create the prerequisites for the development of various phenomena of tectonic layering (lateral shearing, different deformation of layers). To study the distribution of velocity, density and other elastic parameters, the results from a seismic tomography study on P-wave as well as S-wave velocities were used. Using empirical as well as theoretical formulas on the relationship between velocity, density and silica content in rocks, their distribution in the Tien-Shan’s lithosphere has been calculated. In addition, other elastic parameters, such as Young’s modulus, shear modulus, Poisson’s ratio and coefficient of general compressions have been determined. Zoning of different types of crust was carried out for the region investigated. The characteristics of the "crust-mantle" transition have been investi gated. Large blocks with different types of the earth’s crust were distinguished. Layers with inverse values of velocity, density and shear and Young modulus are revealed in the Tien-Shan lithosphere. All of the above described features open new ways to solve geodynamics problems.     

Seismic Shear Waves in Deep Seismic Reflection Surveys: Some Notes on Problems and Profits

—Shear (S) waves differ from compressional (P) waves because of their lower propagation velocities, their lower frequencies and due to the different character of their particle motion. The move-out of travel-time branches of S-wave reflections is different from P waves owing to the difference in the propagation velocities. To distinguish between P and S waves requires broadband-frequency acquisition, long receiver arrays and three-component recording. S-wave generation at the source and P-to-S-wave conversion at crustal interfaces can be very efficient, implying that there is a real danger of misinterpreting signals if only vertical components are used. On the other hand, integrated P- and S-wave studies promise to provide very efficient lithological discriminators in the crystalline crust, in particular concerning the quartz content, and indicators for rock anisotropy, which can be interpreted for the existence of fine layering, the direction of the recent stress regime (alignments of micro-fractures) or for the direction of palaeo-stress (alignments of minerals).