Modelling of sedimentary basins from gravity anomalies with variable density contrast   总被引：3，自引：0，他引：3  

D. Bhaskara Rao 《Geophysical Journal International》1986,84(1):207-212

Summary. The decrease of density contrast with depth in sedimentary basins could be approximated by a quadratic function. The sedimentary basin is viewed as a number of outcropping vertical prisms put in juxtaposition at each observation point. Equations are derived for the gravity anomaly of a vertical prism for a quadratic density function. The initial model is obtained by calculating the thicknesses of the prisms at each station by an infinite slab formula. The differences between the observed anomalies and the anomalies of the initial model at each station are used to modify the initial model. A computer program is developed for initial estimates and refinement of the model. The method is applied to interpret the gravity anomaly of San Jacinto Graben, California, where sediments filling the graben have a density contrast that can be approximated to a quadratic function. Finally the convergence of the method is discussed.  相似文献   

Dynamic topography and gravity anomalies for fluid layers whose viscosity varies exponentially with depth     

Justin Revenaugh  Barry Parsons 《Geophysical Journal International》1987,90(2):349-368

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A Constrained Nonlinear Inversion Approach to Quantitative Interpretation of Self-potential Anomalies Caused by Cylinders,Spheres and Sheet-like Structures     

J.?AsfahaniEmail author  M.?Tlas 《Pure and Applied Geophysics》2005,162(3):609-624

An interpretative method based on a nonlinearly mathematical optimization concept has been developed in this paper, in order to interpret self-potential anomalies (SP) due to horizontal cylinder, vertical cylinder, sphere and sheet-like structures. This interpretative method comprises three main steps. The first step is to formulate mathematically a nonlinearly constrained minimization problem (NCMP) to describe the geophysical problem related to the studied structure. The second one is to suggest an interior penalty function in order to convert the nonlinearly constrained minimization problem (NCMP) into a nonlinearly unconstrained minimization one (NUMP). The third step is to solve the converted nonlinearly unconstrained minimization problem (NUMP) by the well-known Hooke and Jeeves direct search algorithm in order to estimate the geophysical parameters of the studied structure, i.e., depth, polarization angle, electric dipole moment (magnitude of polarization) and geometric shape factor. The Hooke and Jeeves direct search algorithm is purposely chosen for being robust and its application to SP data allows a rapid convergence towards the optimal estimate of parameters. This interpretative method was first tested on theoretical synthetic models with different random noise, where a very close agreement was obtained between assumed and evaluated parameters.The validity of the proposed interpretative method is also tested on practical field examples taken from Turkey, India and Germany, where available SP data existed and was previously analyzed by different interpretative methods. The agreement between the results obtained by the developed method and those obtained by other published methods is good.Acknowledgment Authors would like to thank Dr. I. Othman Director General of the Atomic Energy Commission of Syria for his interest and continuous encouragement to achieve this work. Special thanks to the reviewers for their constructive suggestions aimed at enhancing the quality of this paper.  相似文献   

关键海区海温异常的变化与中国区域降水和气温的关系   总被引：2，自引：0，他引：2  

Zhang Weiqing  Qian Yongfu 《大气科学进展》2001,18(2):294-308

利用 １９５１年到 １９９８年的月平均海温资料及同时期中国 １６０个测站的降水和气温的月平均资料,选用海温异常的变化趋势一变温,讨论了关键海区海温异常的变化与我国降水和气温的关系,旨在探讨变温因子与我国降水和气温的关系与海温距平与降水和气温的关系有什么不同,用变温因子能否降低降水预报的不确定性。结果表明：降水异常对海温异常两种变化趋势的响应不完全相同,说明分别讨论同一种海温异常态的两种变化趋势对降水的影响比单独讨论海温距平对降水的影响更有效一些,有助于降低预报的不确定性;除西太平洋海区外,气温异常对各海区海温异常两种变化趋势的响应较一致。降水异常对变温的响应与对海温异常的响应,有一致之处,也有不同之处。  相似文献   

Resistivity studies over the Flinders conductivity anomaly, South Australia     

S. C. Constable 《Geophysical Journal International》1985,83(3):775-786

Summary. Seven Schlumberger resistivity soundings with maximum current electrode spacings of 20 km have been conducted south of Lake Frome in South Australia. These experiments were done partly to test new electrical sounding equipment and partly to investigate a large conductivity anomaly previously delineated by other workers using magnetometer array and MT methods (the 'Flinders'anomaly). These previous studies left some doubt as to the depth to the conductive region responsible for the anomaly.
The electrical soundings did not detect a buried conductive zone, which constrains it to lie deeper than 5–7 km. However, the study did show the surface sediments of the region to be very conductive; resistivities of 2–9 μm were measured over thicknesses of 50–400 m, with sediment thickness inferred to be up to 2 km to the north of the studied area. This raises the question of whether current channelling in the surface sediments could have been responsible for the earlier results. Simple modelling and application of the criteria given by Jones suggest this may be so.
The equipment used for this study is a low power (200 W), computer controlled system which employs synchronous stacking and other signal processing to achieve signal to noise improvement ratios of up to 1000.  相似文献   

重力异常源深度探讨     

刘晓华 《大地测量与地球动力学》1994,(1)

对不同深度内异常密度的分布与不同阶次谐波分量间的关系作了两种假设，利用ＧＥＭ１０Ｃ地球模型的２～３６阶球谐系数计算了在这两种假设下不同阶次的球谐系数所对应的异常场源深度。结合已知的地球物理信息讨论了本文计算结果的合理性。  相似文献   

Constraints on the deep structure and dynamic processes beneath the Alps and adjacent regions from an analysis of gravity anomalies   总被引：2，自引：0，他引：2  

Hélène Lyon-Caen  Peter Molnar 《Geophysical Journal International》1989,99(1):19-32

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Critical regions: A GIS-based model of marine productivity hotspots     

Vasilis?D.?ValavanisEmail author  Argyris?Kapantagakis  Isidora?Katara  Andreas?Palialexis 《Aquatic Sciences - Research Across Boundaries》2004,66(1):139-148

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Geomagnetic field variations between chrons 33r and 19r (83–41 Ma) from sea-surface magnetic anomaly profiles     

C. Bouligand  J. Dyment  Y. Gallet  G. Hulot   《Earth and Planetary Science Letters》2006,250(3-4):541-560

Sea-surface magnetic profiles exhibit coherent short wavelength “micro-anomalies” (or “tiny wiggles”) superimposed to the main anomalies due to reversals. In this study, we investigate the nature and distribution of these tiny wiggles on oceanic crust formed during the  42 Myr-long period following the Cretaceous Normal Superchron. To this end, we compute stacks of anomaly profiles from different areas in the Indian and the Pacific oceans. Using a simple method based on upward continuation, we demonstrate that, the tiny wiggles are consistent worldwide although their patterns exhibit different resolutions at different spreading rates. They are therefore confidently ascribed to past fluctuations of the geomagnetic dipole moment. A high resolution record of these fluctuations is obtained by selecting and stacking profiles from areas with the highest spreading rates. Modeling the micro-anomalies as short magnetic polarity intervals yields durations for these intervals generally shorter than 10 kyr, likely too short to be indeed “true” subchrons. Moreover, the number of detected tiny wiggles clearly depends on the spreading rate. These results support geomagnetic intensity fluctuations as being the cause of most tiny wiggles, as also suggested by recent magnetostratigraphic data. The tiny wiggles are uniformly distributed within chrons, indicating that paleointensity fluctuations are neither inhibited after, nor enhanced before, a reversal beyond a “blind” zone of about 10 km (corresponding to 80 to 250 kyr depending on the spreading rate) for which the anomalies due to reversals prevent the detection of tiny wiggles. Most tiny wiggles probably represent a filtered record of a uniform secular variation regime, as suggested by their uniform spatial distribution over the whole investigated period.  相似文献   

Fluid migration and location of fractured layers in the crystalline basement by temperature logging in the Volga Region, Russia     

N.N. Khristoforova  A.V. Khristoforov 《Journal of Geochemical Exploration》2006,89(1-3):187

High-precision temperature logging in deep and superdeep wells has permitted the study of the thermal regime in the granite–gneiss layer of the Earth's crust. The long-term logging works have allowed the classification of temperature anomalies recorded in the crystalline basement. Most anomalies have been supposed to be caused by loosely aggregated, permeable zones. The classification reflects main types of processes at a great depth — such as injection, inflow and upward migration of gas-cut fluid. The results of great practical importance are obtained using our classification: some intervals — where temperature anomalies interpreted as inflow reservoirs were revealed — have produced fluid, and others interpreted as injection reservoirs absorbed borehole fluid during tests.  相似文献