地震波速度约束的大横向黏度变化的地幔对流研究

本文将横向黏度变化提高到3个量级,获得了地震波速度结构约束下的大横向黏度变化的地幔浅部的极型场和环型场对流图像.与小横向黏度变化下的结果相比,本文的结果具有显著的改善.对极型场对流图像,主要体现在本文结果能更清楚地解释太平洋板块、大洋洲和南美洲以及东太平洋洋中脊处的现今运动状态;对环型场对流图像,能更合理地解释北太平洋板块的右旋运动.本文计算的极型场、环型场对流速率以及揭示的某些区域如欧亚大陆和非洲大陆的运动状态与现今地表板块的运动速率以及欧亚板块和非洲板块的运动状态有明显差异,但相比小横向黏度变化下的结果,有助于更好地认识和理解现今地表板块运动的深部动力学过程.     

地幔深部运动,全球构造格局及中国地震应力场背景

本文探讨了形成岩石层内部应力场两种可能的力源:地幔对流产生的作用于岩石层底部的切向拖曳力和沿板块边界分布力系对岩石层内应力场的影响.发现这两种力同时作用控制了中国大陆应力场的基本格局,它们产生的应力场主压应力方向和用地震震源机制解、钻孔应力测量及地质构造推断的中国应力场分布基本吻合.     

地幔对流

地幔对流是地幔中．特别是地幔软流层中发生的热对流。地幔对流是一种自然对流．既是发生在地幔中的一种传热方式（通过物质运动传递热量）．又是一种地幔物质的运动过程（由物质内部密度差或温度差所驱使的）．是地球内部向地球表面输送能量、动量和质量的一种有效途径。地幔对流是一个复杂的系统．是在缓慢的进行的,对流活动的时间可达几千万年,甚至几亿年。地幔对流的流动形态可以不同。     

横向黏度变化对球层中热对流的影响

本文在常黏度的基础上,加上横向黏度变化,纯粹研究了横向黏度变化对球层中热对流的影响.结果表明,横向黏度变化可以加速或阻碍球层中的热对流,并对球层中热传输方式有调节作用,但是横向黏度变化对球层中热对流的影响会限制在一定的强度范围内,并且难以改变球层中热对流的格局.横向黏度变化所产生的环型场速度占总速度场的比例最多为十几个百分点,难以解释观测到的地表板块运动中的环型场能量大小.     

地幔深部运动,全球构造格局及中国地震应力场背景c

本文探讨了形成岩石层内部应力场两种可能的力源:地幔对流产生的作用于岩石层底部的切向拖曳力和沿板块边界分布力系对岩石层内应力场的影响.发现这两种力同时作用控制了中国大陆应力场的基本格局,它们产生的应力场主压应力方向和用地震震源机制解、钻孔应力测量及地质构造推断的中国应力场分布基本吻合.     

地震层析成像—地幔对流新模型的研究

利用地震层析成像数据计算地幔对流模型的方法。假设地幔地震层析成像数据对应的地幔横向不均匀结构是地幔热对流的结果，将地震层析成像数据转化为地幔温度不均匀分布。该方法考虑热流体动力学的3个基本方程，以及热输运方程中的非线性项，直接将上述地震层析成像转化的地幔温度不均匀分布作为内部荷载直接引入基本方程，进而反演计算地幔对流的基本格局。理论结果表明，对流格局不仅依赖地震层析成像数据，而且在很大程度上受地幔动力学框架和热动力参数（如Rayleigh数）以及边界条件和系统响应函数的影响。     

地幔对流的数值模拟及其与表面观测的关系

本文从基本的热对流方程出发,并结合地幔对流特点,特别考虑到自重及非线性影响,探讨地幔对流及其与表面观测的关系,发展了相应的数值方法.结果表明,计算得到的长波大地水准面、地表地形、板块速度场水平散度与观测值符合程度较好.上、下地幔的非绝热温度异常与由地震层析得到的地震波速异常显示一定的相关性.地幔内部的流动呈现复杂形态,反映了高瑞利数对流的特征.     

三维地震波速结构约束下的变黏度地幔对流及其动力学意义

建立了三维黏度扰动下的变黏度地幔对流模型,并提供了在引入地幔的三维地震波速度结构下相应的求解方法. 依此反演了瑞利数Ra = 106时,两种不同边界条件下的极、环型场对流图像,这有助于深化对地幔物质流动和大地构造运动的深部动力学过程的认识和理解. 研究结果表明,不但地幔浅部的极型场对流图像显示出了与大地构造运动的相关性并揭示了其深部动力学过程,更重要的是,地幔浅部的环型场对流图像首次为我们认识和理解板块构造的水平与旋转运动提供了重要的信息：环型场速度剖面中在赤道附近存在一条大致南东东—北西西向的强对流条带,可能与环赤道附近大型剪切带的形成相关,进而表明可能是该带强震发生的深部动力学背景;在南北半球存在的旋转方向相反的对流环表明它们整体上可能存在差异旋转.     

Upper mantle lateral heterogeneities and magnetotelluric daily variation data

We use telluric and magnetic data of the diurnal variation recorded in Europe, Australia and North America to study the magnetotelluric tensor in the 6h–24h period range. We use associate directions and we eliminate the effects of deviation of telluric currents. We thus obtain for each observatory reliable phases and apparent resistivity values representative of the neighbouring stratified substratum. It appears that the values obtained in the four European observatories (Saint-Maur, France; Ebro, Spain; Toledo, Spain; Nagycenk, Hungary) give similar results and that these results are different from those obtained either in Tucson (USA) or in Watheroo (Australia).Using Bostick transform we interpret these phase and apparent resistivity values in terms of conductivity of the upper mantle. We discuss then the conductivity heterogeneities in terms of change either in temperature, or partial melting or percentage of fluids of the upper mantle: at depths of about 300 km, the upper mantle appears to be 100 °C hotter under Australia than under Europe; the probable presence of fluids at depths about 100 km in the southwestern North America upper mantle appears to be responsible for the high observed conductivities. All these conductivity values are coherent with tomography results from Woodhouse and Dziewonsky: high (low) conductivities are cohernet with low (high)seismic wave velocities.     

Lateral variation in upper mantle viscosity: role of water

Differences in the viscosity of the earth's upper mantle beneath the western US (∼10¹⁸-10¹⁹ Pa s) and global average values based on glacial isostatic adjustment and other data (∼10²⁰-10²¹ Pa s) are generally ascribed to differences in temperature. We compile geochemical data on the water contents of western US lavas and mantle xenoliths, compare these data to water solubility in olivine, and calculate the corresponding effective viscosity of olivine, the major constituent of the upper mantle, using a power law creep rheological model. These data and calculations suggest that the low viscosities of the western US upper mantle reflect the combined effect of high water concentration and elevated temperature. The high water content of the western US upper mantle may reflect the long history of Farallon plate subduction, including flat slab subduction, which effectively advected water as far inland as the Colorado Plateau, hydrating and weakening the upper mantle.     

The influence of thermochemical convection on the fixity of mantle plumes

A general feature of both isochemical and thermochemical studies of mantle convection is that horizontal plume velocities tend to be smaller than typical convective velocities, however, it is not clear which system leads to a greater fixity of mantle plumes. We perform two- and three-dimensional numerical calculations and compare both thermochemical and isochemical cases with similar convective vigor to determine whether presence of a dense component in the mantle can lead to smaller ratios of horizontal plume velocity to surface velocity. We investigate different viscosity and density contrasts between chemical components in the thermochemical calculations, and we perform isochemical calculations with both free-slip and no-slip bottom boundary conditions. We then compare both visually and quantitatively the results of the thermochemical and isochemical calculations to determine which leads to greater plume fixity. We find that horizontal plume velocities for thermochemical calculations are similar to those from isochemical calculations with no-slip bottom boundary conditions. In addition, we find that plumes tend to be more fixed for isochemical cases with free-slip bottom boundary conditions for two-dimensional calculations, however, in three dimensions, we find that plume fixity is similar to that observed in thermochemical calculations.     

中国地幔结构及物性研究的进展

对2004——2007年中国地球物理学家在地幔内部结构和物质性质方面的研究工作进行了总结. 对地幔结构的地震波速度成像,地幔介质的各向异性,地幔间断面,地幔对流,以及地幔介质物性进行了综述,指出了各方面的主要内容,使用的主要方法和主要结果. 从这4年的研究可以发现,一些原有的研究领域工作更加深入,方法更加先进,而且进行了广泛的国际合作,合作的范围也逐渐扩大,方式多样,并出现了一些新的研究方向.      

Deep mantle flow, global tectonic pattern and the background of seismic stress field in China

In this paper we investigate the sources of two kinds of forces to form the stress field in the lithosphere. These are the drag force caused by mantle flow and the force system along plate boundaries. The results show that both forces control the basic stress pattern in China and compressive stresses can fit with the stress patterns constructed by focal mechanisms,in-situ stress measurements in boreholes and that deduced from other geophysical and geological observation. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 295–306, 1991. This research is sponsored by the Chinese Joint Seismological Science Fundation.     

Nonlinear free thermal convection in a spherical shell:A variable viscosity model

Introduction The velocity field of surface plate motion can be split into a poloidal and a toroidal parts.At the Earth′s surface,the toroidal component is manifested by the existence of transform faults,and the poloidal component by the presence of convergence and divergence,i.e.spreading and subduc-tion zones.They have coupled each other and completely depicted the characteristics of plate tec-tonic motions.The mechanism of poloidal field has been studied fairly clearly which is related to …     

地幔对流与深部物质运移研究的新进展

现代固体地球科学已经认识到,地幔对流不再是少数动力学家的假想,它是地幔热动力系统的主要构架.地幔对流和板块运动驱动机理关系的研究已经从简单的主动或被动驱动的讨论转向对统一热动力系统的探讨.包括地幔热柱在内的地幔对流的深入研究不仅成为研究地幔热动力系统演化的主线,也成为研究大陆形成和演化驱动机理的主线.与此同时,以地震层析成像为主体的地震、地球物理观测资料和以地幔岩石化学组份为主体的地球化学观测成为认识地幔对流的强有力的工具.然而,地球化学和地球物理观测之间存在明显的差异,一些依赖于地球化学数据构思的新的热动力学框架对地幔对流的研究构成了强烈的挑战.