二维倾斜地形对大地电磁资料的影响与地形校正

二维倾斜地形影响,主要使ＴＭ极化模式的视电阻率降低。数值模拟结果证明,倾角小于１０°时,地形影响可以忽略,随着倾角的增大,地形影响急剧加强。同时,倾斜地形影响与周期有关,周期愈长,影响愈甚,而且,当倾角增大时,开始出现显著影响的周期提前。利用带地形均匀半空间与水平均匀半空间的电磁响应,计算出校正系数,进而可以消除或降低地形影响     

Three-dimensional finite element analysis of the seismic behavior of inclined micropiles

This paper presents a thorough study of the behavior of inclined micropiles under seismic loading. Analysis is carried out using a full three-dimensional finite element modeling. The soil media is assumed to be elastic with Rayleigh damping, while micropiles are modeled as 3D elastic beam elements. The structure is described by a single degree of freedom system composed of a concentrated mass and a column. The paper is composed of four parts. The first part includes a literature survey on the behavior of inclined micropiles. The second part presents the numerical model used in this study. The third part concerns analysis related to the influence of micropiles inclination on the seismic behavior of a group of micropiles embedded in a homogeneous soil with a uniform stiffness. The last part deals with the seismic behavior of inclined micropiles embedded in a soil layer with a depth-based increasing stiffness. The results of this study provide valuable information about the influence of micropiles inclination on dynamic amplification and on the seismic-induced internal forces in micropiles.     

Three-dimensional finite strain analysis in the high-grade part of the Sanbagawa Belt using deformed meta-conglomerate

Abstract   Regional ductile deformation of the Sanbagawa belt is generally thought to be characterized by constrictional strain, based on strain analysis using deformed radiolarians in the low-grade regions. Similar strain analysis could not be carried out in the medium- to high-grade zones, because it is very difficult to identify individual radiolarians after strong recrystallization. However, discovery of the first known meta-conglomerate in the high-grade region of the Sanbagawa Belt allows quantitative 3-D strain to be estimated in this region. Using a development of the Rf-φ method, an evaluation of appropriate errors for this estimate can be determined. The principal strain ratios and estimated errors are X/Y = 5.4–6.6 and Y/Z = 3.8–3.9 implying deformation in the flattening field and refuting the idea of uniform constrictional strain. Semi-quantitative markers of the shape of the strain ellipse throughout the high-grade regions suggest that the deformation of the Sanbagawa Belt is dominantly in the flattening field. The difference with the earlier results may be due to late-stage overprinting by upright folding of the main ductile fabric in the low-grade region of western Shikoku.     

On the inclination functions and a rapid stable procedure for their evaluation together with derivatives

The authors’ individual work on the inclination functions over a period of more than 30 years has led to the need for a joint paper. Intervening papers by other authors have demonstrated misunderstandings needing to be corrected, in particular concerning the key recurrence relation published by the present first author in 1971. This relation is remarkably stable, though this has not always been recognized. The real source of error with the specific functions that are involved in the recurrence relation arises from the possibilities for underflow (as well as overflow) in the computation. The problem exists even with normalized versions of the functions, and is carefully addressed. Very important, for both academic and practical reasons, is a general invariance relation that had been found earlier by the second author, for which a proof is given here for the first time. Some numerical results from our new (and highly efficient) procedure for computing the inclination functions are tabulated, and comparisons made with the results of other authors. Finally, Fortran code for an optimized implementation of this procedure is in supplementary material. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

地球表层物质非均匀分布对地球动力学扁率的贡献

全球动力学扁率(H)是研究地球自转与岁差的-个重要物理量.由对岁差的观测有Hobs=0.0032737≈1/305.5.该文依据内部场理论重新计算了流体静平衡态下的地球内部几何扁率剖面,结果与Denis(1989)的结果相吻合.该文还推导了三阶扁率精度下日的计算式,并计算出PREM地球模型的H理论值为HPREM=1/308.5,这与其他人的结果一样,与观测值之间存在1%的差别.为了研究这个差别的来源,该文将PREM模型中均一的上地壳层与海洋层替换为ECCO、GTOPO30和ETOPO5等真实的地球表层数据,结果表明替换后得到的H更加偏离观测值.此结果说明来自于地幔及更深处质量异常引起的正面影响可能要比先前预期的高,并为地壳均衡理论提供了间接的证据.     

Stratigraphic coordinates: a coordinate system tailored to seismic interpretation

In certain seismic data processing and interpretation tasks such as spiking deconvolution, tuning analysis, impedance inversion, and spectral decomposition, it is commonly assumed that the vertical direction is normal to reflectors. This assumption is false in the case of dipping layers and may therefore lead to inaccurate results. To overcome this limitation, we propose a coordinate system in which geometry follows the shape of each reflector and the vertical direction corresponds to normal reflectivity. We call this coordinate system stratigraphic coordinates. We develop a constructive algorithm that transfers seismic images into the stratigraphic coordinate system. The algorithm consists of two steps. First, local slopes of seismic events are estimated by plane‐wave destruction; then structural information is spread along the estimated local slopes, and horizons are picked everywhere in the seismic volume by the predictive‐painting algorithm. These picked horizons represent level sets of the first axis of the stratigraphic coordinate system. Next, an upwind finite‐difference scheme is used to find the two other axes, which are perpendicular to the first axis, by solving the appropriate gradient equations. After seismic data are transformed into stratigraphic coordinates, seismic horizons should appear flat, and seismic traces should represent the direction normal to the reflectors. Immediate applications of the stratigraphic coordinate system are in seismic image flattening and spectral decomposition. Synthetic and real data examples demonstrate the effectiveness of stratigraphic coordinates.     

高精度引潮力计算中地球扁率的影响

计算了地球扁率对月亮和太阳引潮力影响的量级,并对其空间分布特征、频率分布特征进行了分析,以及利用ELP2000-85星历计算了月亮引潮位中地球扁率影响项的调和展开.结果表明,引潮力中地球扁率的影响最大值接近2×10-11ms-2.引潮位调和展开结果中,振幅大于4×10-13ms-2的潮波项共有16项.     

On the Models of the Lower Mantle Viscosity Consistent with the Modern Data of Core-Mantle Boundary Flattening

In Forte and Claire Perry (2000) models of mantle viscosity (by using the data on tectonic plate velocities, of global free-air gravity anomalies, of surface topography corrected for crustal isostasy, and the excess of dynamic ellipticity of the core-mantle boundary in accordance with Herring et al., 1986 and Mathews et al., 1999) have been constructed. In the following investigation we reconsider the results which are obtained from the presently available data on core-mantle boundary flattening (abbreviated by CMBF). In contrast with the aforementioned work, we use below the value of CMBF (Molodensky and Groten, 1998) which is based on a new approach to the theory of diurnal Earth tides and nutation which takes into account the second-order terms of expansions of a small parameter (for a detailed discussion of this subject see (Molodensky and Groten, 1998)). Below we find the area of admissible values of mantle viscosity which does not contradict the following data sets: (a) the numerical value on CMBF; (b) the value of the whole Earth's dynamical flattening, and (c) the data on the secular deceleration of the Earth's rotation. Our estimations show, that the maximal viscosity at depth 2000 km may be of the order of 10²⁷ Poise. This value is consistent with the distribution obtained by Trubitsin (2000) who adopted the viscosity dependence on temperature and pressure by an exponential function with olivine parameters under the assumption that the activation energy varies only weakly with pressure, and the activation volume varies in inverse proportion to temperature. Under these assumptions, his solution of convection equations gave the depth dependence of temperature and thereby the viscosity distribution.     

托换—挤淤法对已建建筑物进行纠偏加固的实践

以苏南某地一建筑物的纠偏加固工程为实例,讨论适合于这类地区的纠偏加固的有效方法：锚杆静压桩托换—掏土、降水挤淤法。概述此方法操作的全过程,总结了它的优缺点。     

青藏高原的形成与隆升

青藏高原的形成与隆升问题是个十分复杂、倍受地球科学家关注的问题。它被认为是冈瓦纳大陆与欧亚大陆长期相互作用的结果。青藏高原是由6个地体相继增生到亚洲大陆上的一个组合,这些地体之间的边界被5条缝合带所限定。造山作用自北向南相继变年轻。青藏高原是特提斯的主要范畴,它可以分成3个区域,分别代表了3个阶段主洋盆位置。特提斯北区位于昆仑山和祁连山,它的遗迹是第五缝合带,在大陆基底上于震旦纪形成裂谷,奥陶纪闭合。特提斯中区位于可可西里-巴颜喀喇,古生代晚期以来在弧后盆地基础上继续破裂、扩张,典型的洋壳形成于石炭-二叠纪,这个时期的洋称古特提斯,它的遗迹为第三和第四缝合带。特提斯南区位于青藏高原南部,雅鲁藏布江缝合带代表了它的主洋盆遗迹,班公-怒江缝合带代表了它的弧后盆地。青藏高原的隆升以多阶段、非均匀、不等速为特征,大体上可分成4个阶段,即45～38,25～17,13～8和3～0Ma。虽然到目前为止已经提出了多种模式来解释高原的形成与隆升,但是这一问题迄今仍然没有解决。文中笔者根据多年来地质。地球物理和地球化学研究成果和近年来新的实验研究结果,提出了叠加压扁热动力模式来解释青藏高原的形成与隆升机制。