共查询到20条相似文献，搜索用时 31 毫秒
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为了提高极地重力数据处理的质量,降低巨厚冰层对重力数据解释的影响,将极地大陆冰盖引起的重力异常从叠加异常中剥离出来成为极地重力数据处理的重要步骤之一。针对该问题,本文建立两个极地大陆冰层构造模型,对不同模型进行正演获得对应布格重力异常,再尝试利用三种位场分离方法,包括趋势分析法、向上延拓法和优化滤波法,对冰层引起的重力异常进行剥离试验,基于模型试验结果对比分析不同位场分离方法对极地冰层重力效应剥离的应用效果。模型试验结果显示,趋势分析法在冰层界面起伏较平缓情况下效果较好,但当冰层界面起伏复杂时难以用数学表达式精确拟合区域场,因此易在结果中引入虚假异常;向上延拓法在局部场源较浅的异常分离中效果较好,但由于极地模型冰盖深度较深及延拓高度选取不合理,在试验中出现了分离不足的情况;优化滤波法在相对复杂模型中分离效果相对好,但由于频段选取的主观性,使得该方法也易出现分离不足或过度情况。综合上述模型试验表明,在剥离极地冰盖引起的重力异常时,由于极地冰盖厚度起伏等地质情况复杂多变,应结合实际地质情况及其他可获得的地球物理资料进行综合分析,选择适用于具体情况的分离方法。 相似文献
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位场场源边界识别是位场数据分析解释中的重点内容之一。相邻异常源由于场的叠加而难以区分,尤其是对于叠加异常中不同深度的场源边界的识别。倾斜角法是位场数据处理中常用的边界增强方法之一,能有效突出低振幅、短波长的异常特征。本文基于倾斜角法定义了新的位场边界探测方法,该方法利用倾斜角方程中位场二阶垂直导数与垂向导数水平导数之比进行计算,能有效区分相邻异常源产生的叠加异常,突出叠加异常中不同深度场源的边界特征。通过综合模型和实测数据,并与现有的基于导数的位场边界探测方法进行比较,评价了该方法的应用效果。结果表明,该方法对场源深度的变化不太敏感,它可以更准确地确定场源边界,区分相邻异常源的叠加异常,尤其对密集型组合地质构造的识别有较好的效果,即使是在场源埋深较大情况下,也能突出叠加异常中不太明显的微弱变化的线性异常特征,以及弱异常源的形态特征,可为精细研究局部地质构造提供技术支持。 相似文献
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时间域激发极化法是应用于金矿勘查的一种重要地球物理勘探手段,以往主要采用中梯扫面和激电测深组合的方法获取激电异常。中梯扫面受限于单一固定供电极距,仅能反映某一深度的激电异常分布;常规对称四极激电测深由于需要对固定测点布设不同极距的供电电极,工作效率较低,并且不适合三维探测。近些年随着大功率、阵列观测技术发展起来的类中梯激电装置可在观测区布设多组不同极距的供电电极,兼顾了激电测深与激电剖面二者的特点,为常年干旱的戈壁滩地区金属矿深部勘查提供了一种可能的探测手段。本文基于类中梯装置大功率三维激电测量技术在甘肃花牛山金矿区开展时间域激发极化法实验工作。实验结果表明：类中梯装置大功率三维激电观测能快捷高效获得研究区不同深度的激电异常;采用与类中梯装置相适应的三维反演方法对激电数据进行三维反演,可获取研究区地下三维精细电性结构;基于矿区的三维电性结构并结合相关地质资料构建的三维地质-地球物理模型,与矿区已知金矿点位置吻合,并发现了三处潜在成矿点;类中梯装置大功率三维激电测量技术在供电困难的戈壁滩地区金属矿勘查中应用效果明显。 相似文献
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Seismological evidence for compositional variations at the base of the mantle transition zone under Japan Islands 总被引：1，自引：1，他引：0
Akira Yamada Dapeng Zhao Toru Inoue Daisuke Suetsugu Masayuki Obayashi 《Gondwana Research》2009,16(3-4):482-490
Temperature and water content anomalies just above the 660-km discontinuity under the Japan Islands are estimated from seismological observations. Two sets of seismological observations of P-wave velocity perturbations and depth variations of the 660-km discontinuity are used, which are (1) long-wavelength (~ 500 km) variations from seismic tomography based on a grid parameterization and waveform analysis of ScS reverberations and (2) moderate-wavelength (~ 150 km) variations from seismic tomography with a block parameterization and receiver-function analysis. To estimate temperature and water content anomalies, partial derivatives of velocity and depth variations with respect to temperature and water content determined by mineral physics studies are used. Under Southwest Japan, low temperature and high water-content anomalies are obtained from both sets of seismological observations, which have already been found by a previous study. Under Northeast Japan, however, there are discrepancies between the results estimated from the two data sets, possibly due to the different resolution scales. This discrepancy is dismissed when examining distributions of the temperature and water content anomalies. These anomalies can be grouped into two geographical locations, one group under Southwest Japan, the other under Northeast Japan. The two groups are clearly separated and exhibit common features in both sets of the seismological observations. The grouping is interpreted by a compositional difference between the subducting Pacific slab under Southwest Japan and a normal mantle under Northeast Japan. 相似文献
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航磁异常深部弱信号提取技术研究 总被引：1，自引：0，他引：1
磁异常通常是地下不同深度磁性地质体产生磁场的叠加,在规范高度的航磁测量结果中,深部磁性体所产生的异常通常表现为弱而平缓,其水平与垂向分辨率均较低,在航磁资料处理解释中难以有效捕获。因此,应用适当方法提取由深部地质体引起的弱磁信息是十分必要的。本文采用精度高且稳定的位场延拓技术将航磁异常向下延拓,可以稳定增强磁异常幅度,随着延拓面与场源之间距离的减小,浅成磁信号与深成磁信号的视深度差异将增大,在对数功率谱上可以将其区分,而后可利用匹配滤波方法将浅部信号剥离,从而得到深部弱信号,同时可计算深部弱信号的视深度。 相似文献
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Maurizio Fedi 《地学学报》1989,1(6):564-572
Poisson's theorem relates linearly the derivative of the gravity potential (taken along the total magnetization vector direction) and the magnetic potential due to a common, isolated source with constant density and magnetization distributions.
From that theorem, two very useful functional transformations for magnetic anomalies were formulated by Baranov, that is the 'pseudo-gravimetric integration' and the 'reduction to the pole'.
In this paper, it is shown that the first transformation is, in some sense, more useful than the reduction to the pole and, further, that its utilization presents noticeable advantages as regards the interpretation of magnetic anomalies. In fact, the pseudo-gravimetric integration, in contrast to the reduction to the pole, also provides a smoothing of the anomaly map and, in particular, reduces the degree of non-linearity existing in the mathematical relationship between the data and the source depth.
In order to show this last property of the transformation, spectral expansion inversions by 21/2 D structures were performed on both magnetic and pseudo-gravimetric synthetic anomalies and the respective speed and precision were compared. The tests clearly indicate that very accurate estimates of the geometric parameters of the known source can be more easily and rapidly calculated by the transformed anomalies. Furthermore, due to its smoothing property, the method seems particularly useful when data are noisy. Tests on real anomalies confirm these results. 相似文献
From that theorem, two very useful functional transformations for magnetic anomalies were formulated by Baranov, that is the 'pseudo-gravimetric integration' and the 'reduction to the pole'.
In this paper, it is shown that the first transformation is, in some sense, more useful than the reduction to the pole and, further, that its utilization presents noticeable advantages as regards the interpretation of magnetic anomalies. In fact, the pseudo-gravimetric integration, in contrast to the reduction to the pole, also provides a smoothing of the anomaly map and, in particular, reduces the degree of non-linearity existing in the mathematical relationship between the data and the source depth.
In order to show this last property of the transformation, spectral expansion inversions by 2
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G. Ramadass S. M. Varaprasada Rao A. Raja Mohammed 《Journal of Earth System Science》1986,95(3):343-349
A simple technique for the interpretation of gravimagnetic anomalies by a numerical differentiation is presented. The ratio of horizontal gradient to the observed field was used for the location of the origin and depth to the causative body. This technique was tested by using fundamental expressions due to sphere, horizontal cylinder and vertical fault models and field data over a spherical body. It has been found that the depth to the centre of the body can be determined accurately by this technique. 相似文献
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应用多次匹配滤波技术进行垂向位场分离 总被引：8，自引：0，他引：8
位场信号的径向平均对数振幅谱可以由多条斜率不同的直线段拟合，直线的斜率即为相应的等效层的深度。当相对于某一参考面，场源深度相对地相差不多时，在对数振幅谱上就难以将其区分，而经过匹配下延处理，场源的深度发生相对变化，选择适当的下延深度，在对数振幅谱上又可区分，此时经第二次匹配滤波又可进一步细分位场信号。这一过程可以反复进行，直到满意为止。这即为多次匹配滤波的思想。最后本文对沙市实测布格重力异常进行了两次匹配滤波处理，比较合理地分离出由基底起伏盐系地层引起的异常 相似文献
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Multiresolution tectonic features over the Earth inferred from a wavelet transformed geoid 总被引：2，自引：0，他引：2
Geoid signals give information about the underlying density structure and can be used to locate the source depth of the mass anomalies. Wavelet analysis allows a multiresolution analysis of the signal and permits one to zoom into a specific area bounded by a particular length scale. The ability of wavelets to resolve the geoid signal into individual wavelength components without losing the spatial information makes this method superior to the more common spherical harmonic method. The wavelet analysis allows one to zoom into a specific area and look at the regional geology. We have used a wavelet transform of the geoid to study the regional geology of Japan and the Philippine Plate, South America, Europe, North America, East Africa and the Middle East, India and the Himalayas, China and Southeast Asia, and Australia. By filtering the Earth’s geoid anomalies with 2-D Gaussian wavelets at various horizontal length scales, one can detect the subduction zones along South America, the Aleutians, and the western Pacific; the Himalayas; the Zagros Mountains; the Mid-Atlantic ridge; and the island chains of the mid-Pacific. We have processed geoid data with a horizontal resolution down to approximately 200 km. Using an adjustable wavelet, one can detect structures that can only be picked up visually with much higher resolution spherical harmonic gravity data. We have also looked at the wavelength at which the maximum signal occurs over a range of scales. This method, known as E-max and k-max, is especially effective for detecting plate tectonic boundaries and ancient suture zones along with areas of strong non-isostatic gravitational potential due to high differential stress. These areas are likely to be at high risk of earthquakes. These methods will be especially useful to future studies of the geoid potentials of other planets, such as Mars and Venus, since they will allow careful studies of the regional geology variations with geoid data of the resolution available from satellites. 相似文献
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向下延拓是重磁数据处理的常用手段,能有效地区分叠加异常、增强浅部异常,但现有向下延拓算法的计算大多是不稳定的,且易受噪声的干扰,往往造成异常形态的畸变.提出一种基于水平导数和向上延拓联合迭代的向下延拓算法,由于向上延拓和水平导数的计算是稳定的,因此该向下延拓方法可有效地增强结果的准确性和稳定性.理论模型试验表明该方法的向下延拓结果比Fourier变换计算结果更加稳定、准确,且受噪音干扰小.将该方法应用于实际数据的处理,结果显示该方法能稳定和准确地完成异常的向下延拓任务,且有效地增强了浅部局部异常. 相似文献
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Mansour A. Al-Garni 《Arabian Journal of Geosciences》2018,11(6):138
Gravity anomalies caused by a thin infinite sheet are interpreted quantitatively based on an integral transform approach which is elegant and simple. The proposed technique depends on the modified Hilbert transform which is called “Sundararajan transform.” The amplitudes of the well-known Hilbert transform and Sundararajan transform are exactly the same but with a phase difference of 270° between them. The interpretation of gravity anomalies due to a thin infinite sheet has been implemented using the Sundararajan transform rather than the well-known Hilbert transform, yielding a straightforward solution. Parameters such as the depth to the top of the sheet (z), the inclination angle (θ), and the amplitude coefficient (K) have been analytically determined using simple mathematical equations. The origin of the causative target can be determined by the intersection point between Hilbert and Sundararajan transforms as well as the intersection point of the amplitudes of the analytic signal of the two transforms. The proposed technique has been first applied to synthetic data where the procedures are clearly illustrated. The effect of noise on the interpretation procedures of the proposed technique has been investigated, showing in general satisfactory results especially depth estimation. However, the most sensitive parameter to noise is the dipping angle, which can be misleading in high level of noise, whereas the least sensitive parameter is the depth. Strictly speaking, the noise does not significantly distort the depth estimation obtained with this proposed technique. Finally, the interpretation of the gravity anomaly across the Mobrun ore body, Noranda, Quebec, Canada, has been carried out using the proposed technique where the parameters are estimated and compared to the results that have been published in literatures using different techniques. 相似文献
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A method coupled with a GUI based code in JAVA is developed in the space domain to simultaneously estimate the structures of strike limited listric fault sources and regional gravity background from a set of observed Bouguer gravity anomalies. The density contrast within the hanging wall of the structure is assumed to be varying continuously with depth based on a parabolic equation. The limiting surface of the fault plane is described with an exponential function. This method is automatic in the sense that it initializes both parameters of a strike limited listric fault source and regional gravity background from a set of observed Bouguer gravity anomalies and improves them iteratively until the modeled gravity anomalies fit the observed anomalies within the specified convergence criteria. The advantage of the code is that besides generating output in both ASCII and graphical forms it displays the animated versions of (i) the changes in model geometry, (ii) variation of each model parameter and misfit with iteration number, (iii) improvements in modeled gravity anomalies, and (iv) variation of density contrast with depth. The applicability of the code is demonstrated on both synthetic and real field gravity anomalies. In case of synthetic example pseudorandom noise is added to the residual gravity anomalies of the structure prior to inversion. The noisy anomalies are then inverted for the unknown parameters presuming (i) an ideal listric fault structure bounded by an exponential limiting surface with perfect flat top and bottom surfaces, (ii) non-ideal structure with uneven top and bottom surfaces with imperfect exponential limiting surface. Further, the robustness of the algorithm is exemplified by adding both regional gravity background and pseudorandom noise to the anomalies of the structure before inversion. In all cases, the interpreted parameters of the structure closely mimic the assumed parameters. The interpretation of gravity anomalies across the master fault of the Chintalpudi sub-basin in India has yielded information that is consistent with both DSS results and drilling information. The highlight of the code is that it can be used to interpret the gravity anomalies of listric fault sources even when the profile along which the interpretation is intended fails to bisect the strike length of the structure. 相似文献
16.
Nanang T. Puspito Yoshiko Yamanaka Takashi Miyatake Kunihiko Shimazaki Kazuro Hirahara 《Tectonophysics》1993,220(1-4):175-192
We present the P-wave seismic tomography image of the mantle to a depth of 1200 km beneath the Indonesian region. The
inversion method is applied to a dataset of 118,203 P-wave travel times of local and teleseismic events taken from ISC bulletins. Although the resolution is sufficient for detailed discussion in only a limited part of the study region, the results clarify the general tectonic framework in this region and indicate a possible remnant seismic slab in the lower mantle.
Structures beneath the Philippine Islands and the Molucca Sea region are well resolved and high-velocity zones corresponding to the slabs of the Molucca Sea and Philippine Sea plates are well delineated. Seismic zones beneath the Manila, Negros and Cotabato trenches are characterized by high-velocity anomalies, although shallow structures were not resolved. The Molucca Sea collision zone and volcanic zones of the Sangihe and Philippine arcs are dominated by low-velocity anomalies. The Philippine Sea slab subducts beneath the Philippine Islands at least to a depth of 200 km and may reach depths of 450 km. The southern end of the slab extends at least to about 6°N near southern Mindanao. In the south, the two opposing subducting slabs of the Molucca Sea plate are clearly defined by the two opposing high-velocity zones. The eastward dipping slab can be traced about 400 km beneath the Halmahera arc and may extend as far north as about 5°N. Unfortunately, resolution is not sufficient to reveal detailed structures at the boundary region between the Halmahera and Philippine Sea slabs. The westward dipping slab may subduct to the lower mantle although its extent at depth is not well resolved. This slab trends N-S from about 10°N in the Philippine Islands to northern Sulawesi. A NE-SW-trending high-velocity zone is found in the lower mantle beneath the Molucca Sea region. This high-velocity zone may represent a remnant of the former subduction zone which formed the Sulawesi arc during the Miocene.
The blocks along the Sunda and Banda arcs are less well resolved than those in the Philippine Islands and the Molucca Sea region. Nevertheless, overall structures can be inferred. The bowl-shaped distribution of the seismicity of the Banda arc is clearly defined by a horseshoe-shaped high-velocity zone. The tomographic image shows that the Indian oceanic slab subducts to a depth deeper than 300 km i.e., deeper than its seismicity, beneath Andaman Islands and Sumatra and may be discontinuous in northern Sumatra. Along southern Sumatra, Java and the islands to the east, the slab appears to be continuous and can be traced down to at least a depth of the deepest seismicity, where it appears to penetrate into the lower mantle. 相似文献
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最佳向上延拓高度的估计 总被引：4，自引：0，他引：4
提出根据两个相邻高度重力异常向上延拓值相关系数与高度的关系 ,以估计应用向上延拓分离区域及剩余重力异常的最佳向上延拓高度的方法。二维模型计算表明 ,不同高度的观测重力异常向上延拓值和观测面上区域重力异常值的互相关系数与高度的关系曲线 ,存在一个明显的极大值 ;这个极大值对应的高度 ,就是从观测异常中分离出这一区域重力异常所需要的最佳向上延拓高度。两个相邻高度重力异常向上延拓值之间的互相关系数与高度的关系曲线 ,存在一个明显的转折点 ,这个转折点对应的高度 ,就是所求的最佳向上延拓高度。应用本方法处理华南北部地区布格重力异常的结果表明 ,由于引起本区区域重力异常的地质因素 ,除了莫霍面及上地壳底面外 ,还受到本区广泛分布甚至出露的花岗岩的影响 ;所以为了从观测异常中分离这一区域异常所需要的最佳向上延拓高度为 2 0 0km ,小于莫霍面及上地壳底界面的平均深度。为了从观测异常中分离出由莫霍面引起的重力异常所需要的向上延拓高度 ,达到 15 0km。因此 ,应用本方法处理实测重力资料 ,必须首先了解引起区域重力异常的场源情况。 相似文献
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Tiran and Sanafir islands and their surrounding areas are very important due to their location within the Red Sea, which is in a triple junction among the African and Arabian plates and the Sinai Peninsula microplate. Consequently, this area should be studied from a geological point of view, particularly because there is a plan to construct King Salman’s bridge connecting Egypt and Saudi Arabia. Freely available potential field data, such as magnetic and gravity data, were integrated with seismological data from nearby seismic stations to understand the regional structure and seismic activity in the area. Potential field data were analysed using edge detection techniques (Tilt DeRivative and horizontal gradient) for qualitative interpretation and 2D inversion modelling for quantitative interpretation. Seismological data were analysed geostatistically to identify many epicentre locations and estimate the focal depths. The results of the potential field data analysis indicate that Tiran and Sanafir islands are located along a subsurface geological edge trending NW, parallel to the Red Sea. A similarity in potential field anomalies between both islands and the southern Sinai Peninsula indicates that these islands were separated from the Sinai Peninsula during the formation of the Gulf of Aqaba via Dead Sea Transform fault. The analysis of the seismic data indicates that a specific motion characterizes each focal depth solution. The seismic events are related to main structural trends NW–SE and NE–SW. 相似文献
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针对时域航空电磁飞行测量数据量大、电导率-深度成像计算时间长,以及三维反演困难等问题,笔者采用三维时域有限差分数值计算方法,计算了多组不同电导率、不同深度的三维异常体电磁响应;通过分析三维异常体剖面曲线的属性特征,提取了7个特征属性参数;基于多元逐步回归法建立了三维异常体的电导率、深度回归方程;通过对方程进行离群值剔除和共线性诊断、显著性检验,最终得到了电导率、深度最优回归方程。对回归方程模型分析和精度分析的结果表明,取样时间为0.2~1.5 ms时：电导率模型的相对误差小于11.95%,残差平方和为4 653.724;深度模型的相对误差小于13.19%,残差平方和为10 873.645。因此,采用多元逐步回归法建立三维异常体电导率和深度方程是完全可行的,是一种有效、准确、快速的识别方法,为野外航空电磁飞行测量时的海量数据异常快速检测和识别奠定了基础。 相似文献