Depths to Lithospheric Magnetic Sources and Lithospheric Thermal Regime under the East Siberian Sea

Izvestiya, Physics of the Solid Earth - Abstract—We present the results of studying the depths to lithospheric magnetic sources under the East Siberian Sea. The azimuthally-averaged Fourier...     

Lithospheric thickness in the western Pacific

Rayleigh wave phase velocities were determined by the single-station method for ten paths in the western Pacific. The data show that even 100 m.y. after formation, the phase velocity and upper-mantle structure are still dependent upon age. Inversion of the data gave a model with a lithospheric thickness of 76 km at 100 m.y., increasing to 104 km at 150 m.y., measured from the base of the crust.     

Combined Effect of Climatic Variations and Groundwater Movement on Observed Heat Flow

In most practical situations, the upper part of a geological section consists of loose sediments, in which heat transfer cannot be described as a purely conductive process. To investigate such situations a one-dimensional numerical model of terrestrial temperature field formation under the combined influence of vertical groundwater filtration and ground surface temperature changes has been developed. The model allows one to consider the perturbation of heat flow interval values resulting from short- and long-period temperature waves propagating into permeable rocks under conditions of advective heat transfer, caused by vertical groundwater filtration. The results show that temperature profiles and interval heat flow values are sensitive to both the paleoclimatic history and the rate of groundwater filtration. The latter plays the prevailing role in the variations of geothermal field parameters, especially within the uppermost part of the loose sediments in unconfined aquifers. The problem was solved for a permeable layer, underlaid by an impermeable layer. This schematisation of water exchange is the typically accepted for hydrogeological analysis. Even at very low rates of filtration the intensity of this effect is enhanced substantially for long-period variations. In the extreme case (for periods of temperature variations of the order of 100,000 years) at typical rates of filtration within the permeable layer, an almost gradient-free zone can be formed down to depths of a few hundred metres. For the case of upward filtration, on the contrary, the influence of climatic variations on the terrestrial temperature field becomes substantially attenuated.     

Geoid anomalies across fracture zones and the thickness of the lithosphere

Recent advances in the measurement and interpretation of geoid height anomalies provide a new way to estimate the thickness of the oceanic lithosphere as a function of crustal age. GEOS-III satellite altimetry measurements show abrupt changes in sea level across fracture zones which separate areas of lithosphere with different ages. These changes have the correct location, amplitude, and wavelength to be caused by the combined gravitational attraction of the relief across the fracture zone and the isostatic support of this relief. Eight profiles of geoid height and bathymetry across the Mendocino fracture zone are inverted to determine the depth of the isostatic compensation, assuming that the compensation occurs in a single layer. These depths are then interpreted with a thermal boundary layer model of lithospheric growth. To explain satisfactorily the geoid measurements, the thermal diffusivity of the upper mantle must be 3.3 × 10^?3 cm² s^?1 and the thickness of the lithosphere, defined as the depth at which the geotherm reaches 95% of its maximum value, must be9.1km m.y.^?1/2 × t^1/2, where t is lithospheric age.     

Lithospheric strength of the Caroline Islands and its tectonic implications

Studia Geophysica et Geodaetica - The Caroline Islands are located in a broad zone near plate boundaries in southwestern Pacific. Accumulating evidence suggests that the hotspot origin alone cannot...     

利用S波接收函数研究华南块体的岩石圈结构

本文基于跨越华夏块体至四川盆地西部的130个线性流动地震台站及其附近90个固定台网台站的观测资料,采用S波接收函数波动方程叠后偏移方法,开展了华南大陆岩石圈结构研究.成像结果显示,研究区岩石圈结构复杂,不同构造单元之间差异显著,构造边界带附近小尺度变化强烈.150 km以上的厚岩石圈主要位于四川盆地,不足100 km的薄岩石圈主要分布于川东褶皱带和华夏块体.雪峰山下方岩石圈厚度显著增加,且以雪峰山为界岩石圈结构和性质存在着显著的东西差异.结合其它地球物理观测得到的地壳-上地幔结构信息,我们提出：（1）四川盆地还保留着厚而冷的克拉通岩石圈根,且岩石圈地幔具有结构分层特征;（2）雪峰山可能是扬子克拉通与华夏块体在西南部的边界;（3）雪峰山以东区域可能经历了岩石圈的减薄和改造,且华南岩石圈的减薄与华北相似,都主体发生在东部地区,造成现今南北重力梯度带两侧强烈的结构差异.研究结果为认识华南大陆的构造演化及其深部动力学提供了地震学约束.

     

Point Mass Method Applied to the Regional Gravimetric Determination of the Geoid

The determination of the local gravity field by means of the point mass inversion method can be performed as an alternative to conventional numerical methods, such as the least-squares collocation. Based on the first derivative of the inverse-distance Newtonian potential for the representation of the gravity anomaly data, it is possible to compute any wavelength component of the geoid in planar approximation with sufficient accuracy. In order to exemplify the theoretical concept, two applications are presented of the computation of two different wavelength components of the geoid, the long wavelength component in a local solution and the short wavelength component in a regional solution. The results are compared with corresponding least-squares collocation solutions, using a global geopotential model to remove and to restore the long wavelength component.     

Microparticles in the Atmosphere from Lithospheric Sources of Technogenic Origin

Izvestiya, Physics of the Solid Earth - Abstract—There is a brief overview of technogenic sources of microparticles associated with the extraction of mineral raw materials and fuel from the...     

大陆岩石圈地幔形成与演化研究的新进展

研究大陆岩石圈地幔形成与演化的主要途径是利用岩石－地球化学探针研究幔源橄榄岩的年龄、组成及其演化，目前多将岩石圈地幔划分为大洋型和克拉通型，并认识到，岩石圈地幔的矿和相、成分、年龄在垂向上具有分层性；根据研究资料，目前已提出了以熔体抽取为岩石圈地幔形成的主要方式，并通过交代、拆沉等过程使岩石圈地幔遭受改造，中国东部岩石圈地幔的成分主体上是饱满的，与其上的太古代地壳并不协调，一些研究者提出了岩石圈拆沉和地幔置换两种具有代有性的模型来解释岩石圈地幔成分的这种特点，人们对中国东部岩石圈地幔作了大量的研究工作，然而，若要形成较为合理的解释，还需应用新技术（如，Re/Os同位素技术）做进一步的工作。     

福建地区岩石圈磁异场的特征分析

利用2014—2015年福建地区4期流动地磁观测资料,得到该地区岩石圈磁场特征信息。经过5km、10km、20km、30km等不同高度的向上延拓处理,对福建地区岩石圈磁场特征信息进行浅部与深部异常场分离,提取深部异常。结果发现在福建长乐—诏安断裂带出现比较明显的磁异常,即在该断裂带南部和中北部发现磁场正负高值的交替变化,这些磁异常与地质构造的分布、地震活动性有一定的关系。     

Lithospheric response to volcanic loading in the Southern Cook Islands

The response of the ocean lithosphere to volcanic island loading has been investigated for the Southern Cook Islands of Rarotonga, Mangaia and the Aitutaki-Mauke group using (1) estimates of the change—with distance from the load—of uplift of islands located on the flexure-created arch, (2) geoid height perturbations as observed with the GEOS 3 and SEASAT radar altimeters, and (3) bathymetric evidence for the moat and arch about the island loads. The effective flexural rigidity for Rarotonga is found to be higher than for the older and nearby islands of Mangaia and Aitutaki. This, together with an earlier result for Tahiti [1], suggests that stress relaxation of the lithosphere has occurred and that this layer behaves as a viscoelastic material with an effective viscosity of about 5–10×10²⁵ poise. The observations for the flexural rigidity do not indicate any dependence on the age of the lithosphere at the time the loading occurred. This suggests that there are no significant differences in lithospheric properties for plates in the age range of 6–7×10⁷ years. Altimeter passes to the east of Mauke indicate that there may be an uncharted submarine extension of the Aitutaki-Mauke chain.     

Lithospheric seismic fabrics of Sulu ultrahigh-pressure metamorphic belt

The Sulu UHP belt is a regional metamorphic belt,consisting of mainly gneisses. It also shows the ex-posed mountain root of a collisional orogenic belt. Themountain root means the thickened crust during theTriassic collision between the Yangtze andSino-Korean cratons. In the Mesozoic, entire easternChine underwent extensive magmatism and volcanism,which caused great changes of lithospheric composi-tion and structures, and leaved some signatures in deepseismic reflection profiles. In recent…     

Far-Zone Contributions to Topographical Effects in the Stokes-Helmert Method of the Geoid Determination

In the evaluation of the geoid done according to the Stokes-Helmert method, the following topographical effects have to be computed: the direct topographical effect, the primary indirect topographical effect and the secondary indirect topographical effect. These effects have to be computed through integration over the surface of the earth. The integration is usually split into integration over an area immediately adjacent to the point of interest, called the near zone, and the integration over the rest of the world, called the far zone. It has been shown in the papers by Martinec and Vaníek (1994), and by Novák et al. (1999) that the far-zone contributions to the topographical effects are, even for quite extensive near zones, not negligible.Various numerical approaches can be applied to compute the far-zone contributions to topographical effects. A spectral form of solution was employed in the paper by Novák et al. (2001). In the paper by Smith (2002), the one-dimensional Fast Fourier Transform was introduced to solve the problem in the spatial domain. In this paper we use two-dimensional numerical integration. The expressions for the far-zone contributions to topographical effects on potential and on gravitational attraction are described, and numerical values encountered over the territory of Canada are shown in this paper.     

嘉峪关地电场观测资料分析

研究了大地电场变化的基本要素,对嘉峪关地电场观测资料的质量进行了评价和分析,得到:嘉峪关台地电场观测基本反映了地电场的真实变化,特别对大地电场变化的记录准确.并研究了嘉峪关台附近及周围发生的4次中强地震前地电场、大地电场短临前兆现象,认为震前都显示了一定的短临异常.     

Lithospheric composition and structure beneath the northern margin of the Qinling orogenic belt

Swarms of mafic-intermediate volcaniclastic bodies occur in the Minggang region of Henan Province, a tectonic boundary between the North Qinling and the North China Block, and emplaced at (178.31±3.77) Ma. These volcanic rocks are subalkaline basaltic andesites and contain abundance of lower crust and mantle xenoliths. Thus this area is an ideal place to reveal the lithospheric composition and structure beneath the northern margin of the Qinling orogenic belt. Geochemical data indicate that these mafic granulites, eclogites and metagabbros have trace elemental and Pb isotopic characteristics very similar to those rocks from the South Qinling Block, representing the lower part of lower crust of the South Qinling which subducted beneath the North China Block. Talcic peridotites represent the overlying mantle wedge materials of the North China Block, which underwent the metasomatism of the acidic melt/fluid released from the underlying lower crust of the South Qinling Block. Deep tectonic model proposed in this paper is that after the Late Paleozoic South Qinling lithosphere subducted northward and decoupled, the upper part of the lithosphere emplaced under the North Qinling and the lower part continuously subducted northward under the North China Block. In Early Mesozoic, the North Qinling Block obducted northward and the North China Block inserted into the Qinling orogenic belt in a crocodile-mouth shape.     

On Gravity Inversion for Point Mass Anomalies by Means of the Truncated Geoid

The physical meaning of the truncated geoid, which is defined by the convolution of gravity anomalies with the Stokes function on a spherical cap of specified radius, has been studied by the authors. They investigated its relation to the density distribution, generating the surface gravity, and its potential use in inversion. Some progress results for simulated studies on point mass anomalies are presented. The behavior of the truncated geoid is controlled by the radius of the integration domain, hereinafter referred to as the truncation parameter, which is treated as a free parameter. The change of the truncated geoid in response to the change of the truncation parameter was studied in the context of the simulated mass distributions. By means of such computer simulations we have managed to demonstrate the clear sensitivity of the truncated geoid to the depths, in addition to the horizontal positions, of point mass anomalies generating the synthetic surface gravity. The objective of this paper is to illustrate, with the help of computer simulation as the method of our study, the contribution of the truncated geoid to the solution of the gravimetric inverse problem. Further work towards employing the truncated geoid in gravity exploration is being conducted.     

青藏高原东北缘岩石圈厚度与上地幔各向异性

利用青海地震台网和甘肃地震台网2007-2009年记录的远震波形资料,提取S波接收函数和SKS分裂参数,得到了青藏高原东北缘的三维岩石圈厚度分布和上地幔各向异性特征.S波接收函数结果表明:昆仑-阿尼玛卿缝合带以南的松潘-甘孜地块东北缘和西秦岭造山带下方岩石圈较薄,厚度为125~135 km;昆仑-阿尼玛卿缝合带以北具有较厚的岩石圈,在昆仑和祁连地块下方岩石圈厚达145~175 km,并向柴达木盆地(175~190 km)和克拉通(鄂尔多斯南部约为170 km、阿拉善南缘约为200 km)下方增厚.上地幔各向异性结果显示:东北缘地区的SKS快波偏振方向为NW-SE向,与前人得到的昆仑断裂带南侧的快波方向存在较大差异,南侧自高原内部呈顺时针旋转,表明昆仑断裂带可能为上地幔变形的转换带.SKS快、慢波延迟时间为0.8~1.9 s,且在昆仑-阿尼玛卿缝合带以北,延迟时间与岩石圈厚度呈正相关关系,推断该区各向异性主要来源于地幔盖层的初期伸展变形.     

基于三重震相的青藏高原东缘岩石圈地幔波速结构

本文利用中国数字地震台网记录到的中国青海和缅甸弧发生的两次浅源地震的区域波形资料,在以Crust2.0改进AK135模型所构建的参考模型C2AK的基础上,通过三重震相波形拟合的方法,获得了青藏高原东部下方从莫霍面至上地幔顶部180 km深度范围内的P波和S波最佳拟合模型。最佳模型显示:松潘—甘孜地块（A和B剖面）下方的P波速度比C2AK模型高5%,而川滇地块（C剖面）下方上地幔顶部的P波速度要比参考模型低5%,且随深度逐渐增加,直至120 km处与C2AK模型值相同;松潘—甘孜地块下方的S波速度较C2AK模型要高3%。上述区域性速度结构差异表明,相对于松潘—甘孜地块,川滇地区的岩石圈地幔存在着更明显的挤出效应。      

Geoid and topography of Venus in various thermal convection models

Important though indirect information about the internal structure of Venus is provided by its topography and geoid. In the last decades this information has been used to constrain the Venus mantle viscosity structure and its dynamic regime. Recently, the geodynamic inversion of the Venus?? geoid and topography resulted in a group of best fitting viscosity profiles. We use these viscosity models here as an input to our mantle convection code. We carry out simulations of the Venus?? mantle evolution in a 3D spherical shell with depth dependent viscosity and check whether the character of the dynamic topography and the geoid represented by their power spectra fits the observed quantities. We compare the results with several other models obtained for different viscosity stratifications (constant, constant with highly viscous lithosphere, linear increase of viscosity). Further, we estimate the effect of other factors such as internal heating and varying Rayleigh number. We use a 2D spherical axisymmetric convection code to study the effect of lateral viscosity variations. In these 2D models we monitor the topography and the geoid developing above the axisymmetric plume and compare them with the observed elevations of Venus?? geoid and topography in several Regia. Though none of the models fits observed data perfectly, we can generally conclude, that the best fit between the observed and predicted quantities is reached for viscosity profiles with 200 km thick lithosphere followed by a gradual increase of viscosity with depth and with the upper mantle viscosity of 2 × 10 ²¹ Pa s. For all viscosity profiles the predicted geoid and topography spectra match the observed ones only up to the degree 40, thus indicating other than dynamic origin of these quantities for higher degrees.     

Numerical Modeling of the Observed Wiechert Seismograph Magnification

—The paper presents results of experiments designed to measure the actual dynamic magnification of the Wiechert 1000 kg horizontal seismometer when excited by seismic waves. This is accomplished by comparing 51 digital records of seismic events recorded by the Wiechert and a well calibrated reference seismometer. The results obtained indicate that the magnification of the Wiechert seismometer is influenced by the interaction of its mass and frame, especially for high frequencies. This interaction has been modeled by considering a system of two coupled pendulums, yielding a theoretical dynamic magnification curve which exhibits main features of the observed magnification. The dis crepancy between the nominal and the actual response of the Wiechert seismograph may lead to errors in studies involving spectral analyses of recorded seismograms, and to overestimation of local earth quake magnitudes.