The Glueckstadt Graben of the North-German Basin: new insights into the structure from 3D and 2D gravity analyses   总被引：1，自引：0，他引：1  

Tamara Yegorova  Yuriy Maystrenko  Ulf Bayer  Magdalena Scheck-Wenderoth 《International Journal of Earth Sciences》2008,97(5):915-930

The structure of the Glueckstadt Graben has been investigated by use of 3D gravity backstripping technique and by 2D gravity and magnetic modelling. Subtracting the gravity effects of the Meso-Cenozoic sediments together with Permian salt reveals a positive residual anomaly within the Glueckstadt Graben. This anomaly includes two local maxima over the Westholstein and Eastholstein Troughs. The 2D gravity models point to the presence of a high-density body within the lower crust of the Glueckstadt Graben. In addition, the results of 2D magnetic modelling indicate that the central part of the high-density body is overlain by an area with high susceptibility. Most probable, the formation of this high-density body is a result of complex poly-phase tectonic history of the study area. Finally, the results of gravity modelling indicate that Permian salt is not homogeneous. 3D gravity analysis and, especially, 2D gravity modelling have distinguished the differences in degree of salt saturation in salt-rich bodies, and elucidate the proportion of Rotliegend salt.  相似文献   

New perspectives on Mars’ crustal magnetic field     

Benoit Langlais  Yoann Quesnel 《Comptes Rendus Geoscience》2008,340(12):791-800

The planet Mars lacks, today, a planetary, dynamic magnetic field, but strong, intense, localized magnetic fields of lithospheric origin, one to two orders of magnitude larger than the terrestrial lithospheric field, are present. This lithospheric magnetic field is the result of magnetization processes in the presence of a magnetic dynamo and of demagnetization processes after the dynamo shutdown, such as impact or volcanoes. This crude scenario can be more accurately specified by interpreting global and local models of the current magnetic field of Mars. Some specific areas are studied, including the intensely magnetized Terra Sirenum, as well as the magnetic anomaly associated with Apollinaris Patera. Magnetic minerals could be of primary and/or secondary origin; this latter would imply an early hydration of a basaltic crust. A scenario, in which Mars experienced a major polar wander due to the Tharsis bulge, prior to the cessation of its dynamo, is proposed and discussed.  相似文献   

利用DInSAR和GPS综合方法估计地表3维形变速率   总被引：2，自引：0，他引：2  

罗海滨  何秀凤  刘焱雄 《测绘学报》2008,37(2):0-249

在分析基于贝叶斯统计和马尔科夫随机场理论的解析优化法的基础上,提出以GPS提供的高精度的水平形变速率作为约束,利用直接分解法,将DInSAR的斜距向形变速率分解成垂直形变速率。试验结果表明,直接分解法有效地综合了GPS的高水平精度与DInSAR的高垂直精度优点,且计算简单,克服了解析优化法可能出现的数值不稳定问题。  相似文献   

地面核磁共振模型约束反演含水层参数   总被引：1，自引：1，他引：0  

张继令  翁爱华 《吉林大学学报(地球科学版)》2008,38(4)

导电模型的地面核磁共振感应电动势是含水量的非线性函数.引入模型约束的迭代反演方法求解该非线性问题的反演.在反演过程中,根据理论公式计算迭代过程中灵敏度矩阵,并采用平坦模型和光滑模型两种约束.对均匀半空间、层状导电模型和实际数据进行了反演模拟,结果表明,模型约束迭代反演方法能从地面核磁共振感应电动势获得含水层较为合理的含水量及分布,且该结果可以从作为初始模型的均匀含水量分布反演得到.对无噪音数据,平坦模型和光滑模型约束对反演的含水量分布影响不大;但当数据存在一定的噪音时,平坦模型约束将比光滑模型约束获得更为精确的含水层参数.  相似文献   

勘查油气田化探新方法——土壤相态烃测量法     

李生郁  徐丰孚 《物探与化探》1993,17(6):441-448

烃气测量是油气化探最主要的方法。目前应用的烃气测量方法有两类:一类是测量土壤中游离烃气如K—V指纹法、吸附丝法、物上气法及直接取土壤气测量法等。此类方法由于需特殊设备及壤气测量方法本身固有的缺陷,目前还未得到普遍应用,另一类为土壤吸附烃气法即国内外目前普遍使用的酸解烃气法、此法在多数油气田上取得好效果,但也有相当多的地区如黄土、荒漠及水网发育等特殊景观区效果不好或不显著。本文介绍一种新的烃气测量法──土壤相态烃测量法。这是用一种特殊的技术,只选择性提取由油气藏渗漏过程中保存在运移通道围岩及近地表土壤各种次生矿物结构中以"穴居"态存在的轻烃组分。"穴居"态烃为累积性的指标,不受外界温度、修水等的影响,保存较牢固,测定结果稳定。相态烃法避免了酸解烃法存在的生物成因烃、矿物同生烃及碳酸盐的干扰影响,提高了测量指标的信噪比,突出了应有的异常。本方法已在黄土厚覆盖区两个已知油气田和一个风成沙覆盖的断裂发育油田上试验获得成功,结果表明相态烃法优于酸解烃法。  相似文献   

Efficient generation of conditional simulations by chebyshev matrix polynomial approximations to the symmetric square root of the covariance matrix     

C. R. Dietrich  G. N. Newsam 《Mathematical Geology》1995,27(2):207-228

Consider the problem of generating a realization y₁ of a Gaussian random field on a dense grid of points ₁ conditioned on field observations y₂ collected on a sparse grid of points ₂. An approach to this is to generate first an unconditional realization y over the grid =_{1 2}, and then to produce y₁ by conditioning y on the data y₂. As standard methods for generating y, such as the turning bands, spectral or Cholesky approaches can have various limitations, it has been proposed by M. W. Davis to generate realizations from a matrix polynomial approximations to the square root of the covariance matrix. In this paper we describe how to generate a direct approximation to the conditional realization y₁, on ₁ using a variant of Davis' approach based on approximation by Chebyshev polynomials. The resulting algorithm is simple to implement, numerically stable, and bounds on the approximation error are readily available. Furthermore we show that the conditional realization y₁ can be generated directly with a lower order polynomial than the unconditional realization y, and that further reductions can be achieved by exploiting a nugget effect if one is present. A pseudocode version of the algorithm is provided that can be implemented using the fast Fourier transform if the field is stationary and the grid ₁ is rectangular. Finally, numerical illustrations are given of the algorithm's performance in generating various 2-D realizations of conditional processes on large sampling grids.  相似文献   

Magnetically-aided evolution of protoplanetary disks     

T. F. Stepinski  M. Reyes-Ruiz 《Astrophysics and Space Science》1995,224(1-2):565-566

We investigate the global evolution of a turbulent protoplanetary disk incorporating the effects of Maxwell stress due to a large-scale magnetic field permeating the disk. A magnetic field is produced continuously by an dynamo and the resultant Maxwell stress assists the viscous stress in p roviding the means for disk evolution. The most striking feature of magnetized disk evolution is the presence of the surface density bulge located in the magnetic gap, the region of the disk where the degree of ionization is too low to allow for coupli ng between the magnetic field and the gas. The bulge persists for a time of the order of 10⁵–10⁶ yr. The presence and persistence of the surface density bulge may have important implications for the process of planet formation and the overall characteristics of resultant planetary systems.Operated by USRA under contract No. NASW-4574 with NASA.  相似文献   

220 ka以来萨拉乌苏河流域地层磁化率与气候变化   总被引：6，自引：7，他引：6  

靳鹤龄  李明启  苏志珠  董光荣  赵晖 《中国沙漠》2006,26(5):680-686

 萨拉乌苏河流域滴哨沟湾剖面磁化率变化结果表明:近220 ka来我国北方气候变化极不稳定,存在着不同尺度的频繁变化,特别是寒冷气候阶段变化尤为频繁,其中倒数第二次冰期存在5个气候旋回,末次冰期存在10个气候旋回。这些气候变化与深海氧同位素、极地冰芯反映的全球变化具有良好的对应关系,反映了该区气候变化与全球变化的一致性。控制本区气候变化的主要因素是全球冰量变化及太阳辐射影响的东亚季风变化。  相似文献   

Effects of magnetic interactions in anisotropy of magnetic susceptibility: Models, experiments and implications for igneous rock fabrics quantification     

Philippe Gaillot  Michel de Saint-Blanquat  Jean-Luc Bouchez   《Tectonophysics》2006,418(1-2):3

Besides granites of the ilmenite series, in which the anisotropy of magnetic susceptibility (AMS) is mainly controlled by paramagnetic minerals, the AMS of igneous rocks is commonly interpreted as the result of the shape-preferred orientation of unequant ferromagnetic grains. In a few instances, the anisotropy due to the distribution of ferromagnetic grains, irrespective of their shape, has also been proposed as an important AMS source. Former analytical models that consider infinite geometry of identical and uniformly magnetized and coaxial particles confirm that shape fabric may be overcome by dipolar contributions if neighboring grains are close enough to each other to magnetically interact. On these bases we present and experimentally validate a two-grain macroscopic numerical model in which each grain carries its own magnetic anisotropy, volume, orientation and location in space. Compared with analytical predictions and available experiments, our results allow to list and quantify the factors that affect the effects of magnetic interactions. In particular, we discuss the effects of (i) the infinite geometry used in the analytical models, (ii) the intrinsic shape anisotropy of the grains, (iii) the relative orientation in space of the grains, and (iv) the spatial distribution of grains with a particular focus on the inter-grain distance distribution. Using documented case studies, these findings are summarized and discussed in the framework of the generalized total AMS tensor recently introduced by Cañon-Tapia (Cañon-Tapia, E., 2001. Factors affecting the relative importance of shape and distribution anisotropy in rocks: theory and experiments. Tectonophysics, 340, 117–131.). The most important result of our work is that analytical models far overestimate the role of magnetic interaction in rock fabric quantification. Considering natural rocks as an assemblage of interacting and non-interacting grains, and that the effects of interaction are reduced by (i) the finite geometry of the interacting clusters, (ii) the relative orientation between interacting grains, (iii) their heterogeneity in orientation, shape and bulk susceptibility, and (iv) their inter-distance distribution, we reconcile analytical models and experiments with real case studies that minimize the role of magnetic interaction onto the measured AMS. Limitations of our results are discussed and guidelines are provided for the use of AMS in geological interpretation of igneous rock fabrics where magnetic interactions are likely to occur.  相似文献   

T -distributed Random Fields: A Parametric Model for Heavy-tailedWell-log Data1     

Jo R?islien  Henning Omre 《Mathematical Geology》2006,38(7):821-849

Histograms of observations from spatial phenomena are often found to be more heavy-tailed than Gaussian distributions, which makes the Gaussian random field model unsuited. A T-distributed random field model with heavy-tailed marginal probability density functions is defined. The model is a generalization of the familiar Student-T distribution, and it may be given a Bayesian interpretation. The increased variability appears cross-realizations, contrary to in-realizations, since all realizations are Gaussian-like with varying variance between realizations. The T-distributed random field model is analytically tractable and the conditional model is developed, which provides algorithms for conditional simulation and prediction, so-called T-kriging. The model compares favourably with most previously defined random field models. The Gaussian random field model appears as a special, limiting case of the T-distributed random field model. The model is particularly useful whenever multiple, sparsely sampled realizations of the random field are available, and is clearly favourable to the Gaussian model in this case. The properties of the T-distributed random field model is demonstrated on well log observations from the Gullfaks field in the North Sea. The predictions correspond to traditional kriging predictions, while the associated prediction variances are more representative, as they are layer specific and include uncertainty caused by using variance estimates.  相似文献