共查询到20条相似文献，搜索用时 965 毫秒
1.
H. LINSSER 《Geophysical Prospecting》1971,19(2):243-252
The considerable increase of sensitivity of new magnetometers allows the elaboration of magnetometric maps with contour intervals of fractions of one gamma. On these maps, small anomalies appear which had never been visible before. They are caused by susceptibility contrasts within the sediments. The areal distribution of these small undulations of the magnetic field depends on tectonics, therefore their analysis can give useful information about the tectonic pattern of the sediments. This paper discusses the automatic transformation of these small anomalies into tectonic units. The problem is solved by a method called Digital Template Analysis which has already yielded very useful results in gravity interpretation. The application of the method described is restricted to surveys executed by high sensitivity magnetometers. Therefore it is supposed that in most oil exploration problems these magnetometers will replace instruments with lower sensitivity. The improved magnetometer surveys in combination with the interpretation method described represent a most efficient, fast and unexpensive reconnaissance method. 相似文献
2.
R. GREEN 《Geophysical Prospecting》1980,28(3):384-391
This paper deals with the practical problem of processing magnetic data in the field, and it shows how the parameters describing a geological contact can be obtained quickly and conveniently on the basis of five measurements. The complete interpretation can be performed in the field using a programmable calculator. For a small ground-party the method greatly improves the quality of the field-work and the interpretation of the magnetic data. The method has been applied to the data from a magnetic survey over the Mooki Fault (Gunnedah-Manilla, N.S.W.), and the results are discussed as an illustration of the efficacity of the method as a field procedure. 相似文献
3.
HELMUT LINSSER 《Geophysical Prospecting》1967,15(3):480-515
Mapping of fault patterns is an important part of geophysical exploration. A computerized digital template analysis method is described which tests gravity maps for the effects of faults by comparing measured gravity data with calculated master curves. The interpreted gravity data are incorporated in a tectonic map using geological symbols and units, for ready use by the geologists. Tectonics can be investigated by gravity detailing if the smallest undulations on the Bouguer map are taken into consideration. Up to now, residual and derivative gravity maps have explained gravity effects by assuming spherical bodies which are almost unknown in geology. The method discussed here uses tectonic elements, such as fault-blocks and dikes as a basis of interpretation instead of the spherical bodies of the conventional interpretation methods. Gravity data can be easily and relatively cheaply obtained in the early phases of exploration by area wide spot coverage following lines of easy access such as roads, etc. Seismic studies, by contrast, have the disadvantage of being executed along predetermined profile lines. Only after sufficient detailing do seismic profiles permit-if at all -an areal mapping of faults. Thus a tectonic map is obtained only at the end of a geophysical survey instead of being available prior to the planning of costly seismic profiles. The use of gravimetric data and their interpretation by the suggested method provides tectonic detail maps in the early phases of geophysical studies. In addition, this article discusses a general geophysical interpretation method, using the investigation of faults by gravity as an example. Applications of this method for different gravity and magnetics problems as well as for combined interpretations are outlined. Detailed case histories will be published in later articles. 相似文献
4.
G.J. PALACKY 《Geophysical Prospecting》1981,29(1):60-88
Since its development some thirty years ago, the airborne electromagnetic (AEM) method has been primarily used as a tool for mineral prospecting. However, advanced AEM systems are capable of other tasks, such as geological mapping and groundwater exploration. Excellent correlation between maps of apparent conductivity and geological maps was observed in several regions of Brazil where AEM surveys were performed. The degree of correlation seems to depend on the local climate. In humid and subhumid tropical regions, a weathered layer develops whose thickness and conductivity depend upon bedrock lithology. Therefore certain lithological types can be recognized from their conductivity signature; e.g., granites and Precambrian coarse clastic rocks are resistive, metavolcanic (particularly mafic) and volcanic rocks are conductive, Phanerozoic sediments are generally highly conductive. Two geophysical surveys are analyzed in the paper. The first was conducted with the time-domain, towed-bird AEM system in the Itapicuru greenstone belt in the state of Bahia. The apparent conductivity map correlated better with the local lithology than the magnetic map. Results of the AEM survey were successfully used to improve the regional geological map. A helicopter EM system was used in the second survey, which covered a portion of the Precambrian shield of Rio Grande do Sul. Also in this region ground checks confirmed the usefulness of conductivity surveys in geological mapping. The technique outlined in the paper holds great promise for countries of humid tropical climate, where few outcrops exist and access is often difficult. The tests performed in Brazil indicate that by executing AEM/aeromagnetic surveys during initial stages of mapping and exploration programs, time and expenditure required for geological field work can be considerably reduced. The resulting geological maps are more accurate and the inventory of mineral occurrences becomes more complete. 相似文献
5.
Herbert Henkel 《Pure and Applied Geophysics》1976,114(2):235-249
Summary Over the shield region of Northern Sweden, the Geological Survey runs a low altitude (30 m) aeromagnetic survey and regional gravity surveys cover almost the same areas. The production of detailed geological maps would be almost impossible without these geophysical measurements. To enhance their interpretation, a study of the appropriate petrophysical properties was started by measurements of density, susceptibility and remanence on all rock specimens collected by field geologists. Up to now more than 30,000 specimens have been measured and almost as many in situ susceptibility determinations have been made. About 10% of the samples are oriented. The information obtained is useful not only for the direct interpretation of geophysical surveys but also reflects the effects of various geological processes acting during and after the formation of the rocks considered.In precambrian rocks, density is obviously closely correlated to mineral composition and thus to chemical composition. This is demonstrated for igneous rocks by the correlation trends between density and SiO2-content and the CM/AF-index.Susceptibility mainly reflects the magnetite content of rocks. As magnetite is an accessory mineral it is seldom considered by geologists. However, a closer study of the magnetic susceptibility of rocks reveals that its extreme complexity reflects the effects of primary and secondary geological processes. The susceptibility spectrum of a certain rock may prove to be a useful classification tool — at least regarding intermediate and basic igneous rocks.The combination of the physical parameters density and susceptibility in 2-dimensional frequency distributions seems to be a promising approach to the understanding of certain petrological processes and makes possible the delineation of local or regional secondary processes. Magmatic differentiation and serpentinization can be demonstrated in this manner.Remanent magnetization plays a secondary role in the majority of precambrian rocks. Still there are places where the natural remanence dominates and shows pronounced directions deviating from today's magnetic field. So far we have only one case where a follow up by demagnetization has been attempted, but intensified paleomagnetic research should most certainly add to our understanding of precambrian geology.Combination of susceptibility and remanance shows some characteristic correlations for highly remanent rocks, reflecting mainly exosolution phenomena among magnetic opaques and grain size distributions. Even these features might be used as diagnostic or classifying tools. They also explain some of the diversity of susceptibility spectra. 相似文献
6.
M. K. SEGUIN 《Geophysical Prospecting》1975,23(3):471-491
The present paper shows the practical use of a combined electromagnetic and magnetic helicopter transported system in the search for steeply dipping high-grade magnetic taconite bodies (magnetic ribbons). The principles of operation of the heliported system and the essential parts of the instrumentation are described. The quantitative interpretation of the data allows the geophysicist to calculate the tonnage of magnetite within the iron ores and to obtain an approximate idea of their grade. According to the tonnage and grade calculations obtained from the surveys, three regions in the west-central sector of the Labrador trough (Wishart Creek, Knob Lake Ridge, and Swampy Bay areas) appear to be the most interesting locations for the site of a magnetic taconite deposit (the Howells River area, which has been evaluated previously, is excluded from the discussion). The tonnages calculated by this geophysical method are not to be compared with probable or possible mineable ore reserves, but are only rough estimates in terms of mining engineering standard. The physical parameters determined with such a system are also used as a tool for indirect geological mapping of the areas flown when interpreted carefully. Practical examples related to results obtained on the magnetic iron formations of the Schefferville mining district are presented. 相似文献
7.
S. Ruelleu F. Moreau O. Bour D. Gapais G. Martelet 《Journal of Applied Geophysics》2010,70(2):161-168
Classically, geological surveys of water resources in hard-rock aquifers are made from aerial photographs or geophysical techniques that basically permit to detect vertical features. On the other hand, aquifers only linked to vertical structures are very limited in space and offer in most cases very poor water resources. In the present case, we do show that an outstanding aquifer in Brittany is linked to a geological context associated with low-angle faults possibly directly connected with vertical feeders. In particular, we show through a high-resolution gravimetric survey that the highly fractured contact between granite and micaschists, which constitutes the main path for groundwater flow, is a gently dipping structure. Combined gravimetric, magnetic and geological data allowed us to establish the overall aquifer geometry by running a three-dimensional forward model. In addition, details about the shape of the contact have been obtained using an iterative scheme based on the method of Oldenburg (1974). The gravimetric model confirms the presence of sub-vertical faults that may constitute important drains for the aquifer recharge. Thus, the geological context associated with exceptional water resources for this crystalline aquifer is characterized by a sub-horizontal to gently dipping contact between granite and micaschists. Only such a geological context can allow sufficient recharge to provide the main water supply for a town of 18,000 inhabitants at an average rate of about a billion of cubic meter per year since 1991. Thus, instead of looking for possible vertical structures like in classical hard-rock hydrogeology, it appears much more efficient to detect sub-horizontal permeable fractures and faults for providing consistent water resources. 相似文献
8.
论述了重磁异常对应分析方法原理和地质解释的地球物理基础,计算了南北构造带北段上延5 ～50km 的重磁对应分析的相关系数R和斜率α的平面分布曲线,结合其它地质和地球物理资料,初步分析认为:(1) 中朝准地台的阿拉善台隆和鄂尔多斯台缘隆起区属于正常地壳结构;鄂尔多斯台缘坳陷区属于非正常地壳结构;(2) 祁连秦岭褶皱区地壳结构比较复杂,南、北祁连和礼县 柞水褶皱带的地壳为基本正常地壳结构;祁连北部走廊过渡带、中部隆起带和南秦岭褶皱带西段的地壳属于非正常地壳结构;(3)相关系数转换带的平面分布特征大致反映了断裂带的伸展方向,在剖面上的位置大致与断裂带构造位置相对应 相似文献
9.
A discussion is given of the requirements, the advantages and the methods to be considered in attempting the quantitative interpretation of gravity or magnetic fields from computed maps of the vertically derived field. The transform which is used here is the first vertical derivative (or vertical gradient) with or without downward continuation, but the computed maps are in fact obtained by a controllable Fourier method in which two kinds of operations can be simultaneously performed in complete independance: on one hand the separation of any part of the data by frequency cut-off, and on the other hand the transformation by vertical derivation or continuation of the part which is retained. Taking as raw data either actual surveys or artificially constructed maps, it is first shown how separated and transformed maps of this type can be efficiently obtained under quite flexible conditions, using a special computer program. It is further seen that for correctly controlled filterings the accuracy of the computed maps actually permits to take them as the basis for quantitative interpretation. To effect this, any one of the conventional methods which make use of equivalent model computations may in the first place be adapted to the interpretation of gradients, with the benefits, however, of an enhanced lateral separation of the anomalies and of a large attenuation of the regional effects. Particularly, the delineation of horizontal contours for even fairly complex models can often be made directly in a sufficiently safe way on the anomalies as they show on the vertical gradient maps. This greatly accelerates the process of determining equivalent model bodies. More special methods of interpretation can also be designed by taking into account first the fact that the vertical derivation of the field amounts to an operation of separation on the field's sources themselves, and in addition the availability of the frequency form of the information as a result of using a Fourier method of transform computation. Trial utilisations of various such interpretation processes of either the conventional or the less conventional type, are presented especially in connection with an interpretation study on transformed maps of parts of an offshore aeromagnetic survey (English Channel). 相似文献
10.
本文提出了一种全张量磁梯度数据的斜导数边界识别方法,该方法利用全张量磁梯度数据定义了北向斜导数、东向斜导数和垂向斜导数.模型试验表明,北向和东向斜导数无法有效识别磁性异常体边界,异常形态复杂虚假异常较多,而垂向斜导数在高纬度斜磁化或者垂直磁化条件下可以清晰而准确得识别地质体的边界,具有一定的深度识别能力.与现有磁张量梯度的边界识别方法相比,识别效果好,可以有效均衡不同深度地质体的响应.将上述方法应用于大兴安岭地区实测航磁三分量数据转换得到的全张量数据,获得了研究区浅部磁性体的分布,并与三分量数据进行联合解释,取得良好的地质效果. 相似文献
11.
Pauline Le Maire Lionel Bertrand Marc Munschy Marc Diraison Yves Géraud 《Geophysical Prospecting》2020,68(7):2307-2319
Magnetic measurements with an unmanned aerial vehicle are ideal for filling the gap between ground and airborne magnetic surveying. However, to obtain accurate aeromagnetic data, the compensation of magnetic effects of the unmanned aerial vehicle is a challenge. Typically, scalar magnetometers are towed several metres under the unmanned aerial vehicle to minimize its magnetic field. In this study, a fluxgate three-component magnetometer is attached 42 cm in front of the unmanned aerial vehicle at the tip of a composite pipe. Using a scalar calibration, the sensor can be calibrated, and the permanent and induced magnetic fields of the unmanned aerial vehicle can be compensated. The contributions of the magnetic measurements at different altitudes to the unmanned aerial vehicle results were tested over an area of 1 km² in the Northern Vosges Mountains. The area is located in a hamlet surrounded by a forest where few geological outcrops are observed. Three magnetic surveys of the same area are obtained at different altitudes: 100, 30 and 1 m above the ground. The unmanned aerial vehicle magnetic data are compared with a helicopter aeromagnetic survey at 300 m above the ground and a ground magnetic survey using upward continuations of the maps to compare the results. The magnetic maps (300, 100, 30 and 1 m above the ground) show very different magnetic anomaly patterns (e.g. amplitude, shape, wavelength and orientation). The magnetic data at different altitudes improve the understanding of the geology from the local to more general scales. 相似文献
12.
L. SZARKA 《Geophysical Prospecting》1987,35(4):424-444
A combined application of two independent direct current geoelectric methods, potential gradient mapping (PM) and magnetometric resistivity (MMR), is proposed for the investigation of high-resistivity basement structures. From a one-dimensional relation between horizontal electric and magnetic fields (due to currents originating from point electrodes placed on the surface of a two-layered half-space having a high-resistivity basement) several advantages of the combined PM-MMR method are shown for two-dimensional and three-dimensional basement structures. Three-dimensional models have been studied by analogue modeling experiments. This new mapping method embraces two parameters: the horizontal electric conductance map, derived from the ratio of the related electric and magnetic components, and the gradient map of their product. A close relation between structural forms and anomaly maps is obtained by using two orthogonal source-electrode layouts. Based on model results a two-channel measuring instrument was developed. The method and the instrument were tested near Sopron where a gradual deepening of, and faults in, the Paleozoic basement were found. 相似文献
13.
Inversion of gravity and/or magnetic data attempts to recover the density and/or magnetic susceptibility distribution in a 3D earth model for subsequent geological interpretation. This is a challenging problem for a number of reasons. First, airborne gravity and magnetic surveys are characterized by very large data volumes. Second, the 3D modelling of data from large‐scale surveys is a computationally challenging problem. Third, gravity and magnetic data are finite and noisy and their inversion is ill posed so regularization must be introduced for the recovery of the most geologically plausible solutions from an infinite number of mathematically equivalent solutions. These difficulties and how they can be addressed in terms of large‐scale 3D potential field inversion are discussed in this paper. Since potential fields are linear, they lend themselves to full parallelization with near‐linear scaling on modern parallel computers. Moreover, we exploit the fact that an instrument’s sensitivity (or footprint) is considerably smaller than the survey area. As multiple footprints superimpose themselves over the same 3D earth model, the sensitivity matrix for the entire earth model is constructed. We use the re‐weighted regularized conjugate gradient method for minimizing the objective functional and incorporate a wide variety of regularization options. We demonstrate our approach with the 3D inversion of 1743 line km of FALCON gravity gradiometry and magnetic data acquired over the Timmins district in Ontario, Canada. Our results are shown to be in good agreement with independent interpretations of the same data. 相似文献
14.
Ó. Pueyo-Anchuela A.M. Casas-Sainz A. Pocoví Juan M.A. Soriano 《Journal of Applied Geophysics》2011,75(2):151-160
In this work we analyse the applicability of amplitude grid maps to the routine of geological surveys by means of GPR (ground penetrating radar). Although amplitude grid maps have been commonly used in archaeological surveys, their use in geological prospecting (including the detection of voids and determination of the internal geometry of sedimentary bodies) is not widespread. The direct analysis of GPR-profiles permits the analysis of geometrical features and other qualitative aspects that can be related to changes in EM properties. Aspects such as changes in the density of the banded disposition in radargrams, loss of reflector definition or higher scattering in particular zones of the profiles can give useful, though non-quantitative, information. The GPR wave-amplitude is a qualitative measurement of magnetic properties that can be processed as a semi-quantitative layout. The main differences observed in changing wave amplitude are related to the surveyed materials and their geometry. These changes produce variations in the relative wave amplitude or vertical wave-phase changes related to differences in the propagation velocity, the attenuation factor, the reflectivity and the geometry of the materials. Maps based on the lateral correlation between profiles (C-scans) or the lateral correlation of wave amplitudes along the same profile (as a tomography or Am-scans) permit the analysis of these changes. Variations in amplitude grid maps or Am-scans are related to (i) geometrical changes of surveyed materials, (ii) changes in the dielectric constant, and (iii) changes in the potential penetration depth (higher attenuation in particular zones of a profile) than can be correlated to the type, state or clay content of subsoil materials. Direct analysis of exposures helps to constrain interpretation using the geometrical features in radargrams resulting from the geological structure. In the same way, analysis of geometrical features in radargrams, together with time-slices of C-scans, can be used to determine the areal distribution of changes in the subsoil and approach the changes in EM properties. An example with parallel profiles and different devices, constrained by means a broadband multifrequency EM survey is shown. 相似文献
15.
AJIT K. SINHA 《Geophysical Prospecting》1983,31(4):627-648
Airborne electromagnetic methods are most commonly used in mineral exploration. However, new developments, such as multifrequency capability and digital on-board field recording, as well as improvements in instrumentation resulting in high signal-to-noise ratios in recorded data, have made their application in geological mapping possible. A three-frequency airborne EM survey carried out over an area northwest of Timmins, Ontario, was interpreted in terms of thickness and resistivity of the layers of a two-layer earth section. Since both in-phase and quadrature components are measured, this provides six independent parameters at each point in space. Based on prior geological information and a preliminary interpretation of the field records, two two-layer models of the subsurface seemed to be appropriate for most of the survey area. An automatic computerized interpretation procedure was devised to interpret the field data at each point in terms of thickness and resistivity parameters of those two models. When the geology is more complex, the data do not fit the models and no interpretations are made. Two maps illustrating the variation of the resistivity and the thicknesses of the layers were constructed from the interpreted data. These maps agree with the known geological information about the distribution of glacial clay in the area. Areas where the layered models do not fit are known to be areas where the geology is complex with a large number of dykes and other lateral inhomogeneities. The study shows that multifrequency airborne EM surveys can be very useful in geological mapping over inaccessible terrain and can significantly help the mapping geologist where outcrops are scarce. 相似文献
16.
M.S.M. Mantovani V.H.A. Louro V.B. Ribeiro H.S. Requejo R.P.Z. dos Santos 《Geophysical Prospecting》2016,64(1):216-227
The Catalão I alkaline–carbonatite complex, which is located in Central Brazil, is one of the main producers of niobium and phosphates in the world. It has been intensely studied geologically and geochemically for its economic potential. This work presents a geophysical analysis over this complex, identifying its behaviour in the subsurface and in portions that have not been explored yet. Different geophysical methods and techniques were applied to achieve the most reliable results possible: at the surface, through radiometric, geological, and topographic data, and at depth, by geological, magnetic, and gravimetric data. The analysis was successfully completed with inversions of gravity and magnetic data that resulted in quite similar models, both in volume and shape. Their density and magnetic susceptibility contrasts were consistent with the expected dunite–pyroxenite lithology from the original mafic intrusion and indicated (by exclusion) the volume of the carbonatite body, which along with the known contents of phosphates and niobium allowed an indirect estimate of the reserves and resources of the complex. 相似文献
17.
首先讨论倾角测井资料自适应窗长人机交互式对比方法．依据地质背景资料对倾角测井电导率曲线进行粗略分层，然后电脑进行精细对比，最后人的知识和经验对对比结果进行确认与解释，从而保证每个资料点对比结果的可靠与客观性．同时讨论了智能型知识库支持下的倾角测井资料交互式构造解释方法，采用人机交互技术识别地层倾角矢量模式组合。然后完成交互式地质解释过程．实践表明，上述方法在复杂地下地质条件和井眼条件下是一种有效而快速的方法，同时可以克服倾角测井资料地质响应的多解性． 相似文献
18.
Aeromagnetic gradient data needs to be reduced to the pole so that it can be better applied to geological interpretation through theoretical derivation. In this paper, we conduct research on the morphological characteristics of the total and horizontal gradient modules before and after reduction to the pole and design models at different latitudes, with consistent and inconsistent magnetic field direction and geological body magnetization direction. We discuss how to use the total gradient module and horizontal gradient module in geological interpretation. The reduced-to-the-pole (RTP) method is required for the horizontal gradient module method but not for the total gradient module. Finally, the conclusions derived from the theoretical models are verified through analysis of real data. The position determination of a geological body using the total gradient method, gradient data, or total-field data works better without RTP, ensuring data primitive authenticity. However, the horizontal gradient module should be reduced to the pole to determine the boundary of the geological body. Finally, the theoretical model is verified by actual data analysis. Both the total and horizontal gradient methods can be applied to geological interpretation. 相似文献
19.
Paulo Roberto Antunes Aranha Cristina Helena Ribeiro Rocha Augustin Frederico Garcia Sobreira 《Journal of Applied Geophysics》2002,49(4)
Ground penetrating radar (GPR) has been used as a tool to access information about ground subsurface features. Such information is very important for different types of studies, varying from those related to archeological research to those studying geological elements of bedrock. More recently, however, GPR has been increasingly applied to environmental studies, especially for soil research. This paper presents the results of an application of GPR for the study of weathered profiles. GPR was used to discover the degree of trustworthiness of the information on the ground subsurface through the interpretation of the results of the radar sections as well as the data collected from boreholes, which reached until 21 m. The results show a relatively high degree of details obtained by GPR, indicating the possibility of speeding up ground subsurface surveys related to geomorphological, geological, and pedological studies. 相似文献
20.
针对任意各向异性地层,利用极向型和环向型标量位函数,导出相应的直流电视电阻率和磁电阻率的磁场响应关系.计算了各向异性地层的直流电视电阻率和磁电阻率响应特征,重点分析了电阻率测深方法与磁电阻率探测方法对地下各向异性介质的探测能力.文中采用状态矩阵的分析方法,首先采用极向型和环向型标量位构造了各向异性层状介质电场与磁场的通解,利用各层界面电场、磁场的连续性及地面激励源的耦合条件,推导了不同层之间电磁场的状态矩阵,建立了空间电场与磁场的递归计算关系.其次,针对递归计算中指数项数值计算的不稳定性,借用状态矩阵的性质,导出了将不稳定指数计算项转化为稳定的指数项的转换关系.针对横向各向同性(TI)介质中极向位与环向位解耦的特点,导出了电磁场的直接积分解.最后,采用解析解验证了算法的正确性,给出了多层各向异性地层模型的视电阻率和磁场响应曲线,分析了直流电法探测裂缝性地层、估计裂缝分布性状的可能性. 相似文献