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1.
以湖南地区为例,利用超高阶地球重力位模型EGM2008计算了研究区的重力大地水准面,并采用棱柱体公式和球体公式相结合的方法分别进行了完全地形改正和Airy-Heiskanen局部均衡改正,得到布格大地水准面和均衡大地水准面.对三种大地水准面进行不同波长分量的分离处理,得到包含不同深度异常信息的剩余大地水准面,并结合其他地球物理资料对研究区进行了详细的地球物理解释.结果表明,剩余重力大地水准面可以有效地反映出研究区内的深部构造特征,如深大断裂带分布、构造块体位置、上地幔密度横向分布等,但对地壳内异常结构反映不明显;研究区岩石圈密度变化相对平缓,厚度由东向西增加;根据剩余均衡大地水准面及研究区Airy局部均衡莫霍面,可以大致推测出研究区的莫霍面起伏形态以及均衡状态,可作为一种有用的参考信息. 相似文献
2.
将地形高、地球内部质量异常以及重力、大地水准面展开成球谐级数,依据岩石圈弹性挠曲均衡补偿理论建立地形—均衡补偿重力、大地水准面异常的球谐级数表达式.由此我们可以研究地形—均衡补偿重力、大地水准面异常与球谐级数阶次的关系,以及不同波长地形荷载与岩石圈挠曲补偿的关系,探讨地形—均衡补偿重力、大地水准面的频谱特性.从观测大地水准面异常和自由空气重力异常扣除地形—均衡补偿大地水准面、重力异常,可以得到均衡大地水准面异常和均衡重力异常.均衡大地水准面异常已经消除了浅层物质不均匀的影响,反映的是地球深部物质密度不均匀分布.均衡重力异常显示出中短波长特性,反映的是地壳上地幔物质分布的失衡和物质调整的动力学特征. 相似文献
3.
本文利用地面实测重力资料和地形高程资料,采用普拉特-海福特(Pratt-ttayford)重力均衡理论模型,取1°×1°方格网,通过使用现成改正表格查取改正值与个别计算点用理论公式计算作校核的方法,计算了我国东北地区75个计算点的均衡重力异常值;并对局部第四系覆盖较厚地区作了第四系密度改正;在此基础上,构制了我国东北N39°—49°,E121°—131°大部分地区的均衡重力异常图;结合区域布格重力异常和区域空间重力异常特征以及莫霍界面的起伏特点作了对比分析和讨论 相似文献
4.
The effects of topographic masses on satellite gradiometric data are large and in order to reduce the magnitude of these effects
some compensation mechanisms should be considered. Here we use the isostatic hypotheses of Airy-Heiskanen and the recent Vening
Meinesz-Moritz for compensating these effects and to smooth the data prior to their downward continuation to gravity anomaly.
The second-order partial derivatives of extended Stokes’ formula are used for the continuations over a topographically rough
territory like Persia. The inversions are performed and compared based on two schemes of the remove-compute-restore technique
and direct downward continuation. Numerical results show that the topographic-isostatic effect based on Vening Meinesz-Mortiz’s
hypothesis smoothes the data better than that based on Airy-Heiskanen’s hypothesis. Also the quality of inversions of the
smoothed data by this mechanism is twice better than that of the nonsmoothed ones. 相似文献
5.
The gravity anomaly has been computed above isostatic, thermally-balanced speading centers that cool by conduction through their top surfaces. Isothermal, and therefore isodense, surfaces were treated as topographic boundaries between layers of different density, and Fourier transforms of power series of the topographic height were used to find the gravity. Convergence requires that the anomaly tend to zero with increasing distance from the ridge crest, and when this is obtained, a crestal positive anomaly is flanked by compensating negatives. Both the magnitude and the spatial width of the anomalies decrease with increasing spreading rate.The ～5 mgal gravity anomalies observed over fast-spreading ridges are matched well by the calculations, but slow-spreading ridges usually have a central rift valley in place of the smooth crest of the idealized isostatic thermal model. The mass deficiency of the valley cancels out the ～40 mgal positive peak that would otherwise occur. The short-wavelength anomaly amplitudes of such ridges are less than 25 mgal and follow the observed local rift valley and flanking ridge topography closely. Excess positive gravity and topography of the flanking ridges suggests compensation of the mass deficiency in the rift valley. However, long-wavelength gravity anomalies such as those observed in the northern Mid-Atlantic cannot be due to topography that is isostatically compensated at a shallow depth. These must be caused either by dynamic forces or by large-scale density differences compensated at much greater depths. 相似文献
6.
高精度金星重力场的获取,是金星探测的重要内容.本文利用最新的金星地形和重力模型,通过高通滤波后的残差地形（RTM）并在考虑均衡改正的情况下改进了重力的短波成分,最终提出了一个新的金星重力模型VGM2013,该模型赤道分辨率达10 km量级,大大高于现有的金星重力场模型,最终结果是金星表面重力加速度和重力扰动.研究中同时发现金星在Airy-Heiskanen均衡模型下的全球最优补偿深度为30 km,金星地壳的密度可能小于当前认为的2700~2900 kg·m-3.VGM2013模型的结果可为将来的金星探测器定轨和着陆导航提供参考,作为重力计算的先验模型.但由于该模型没有包含短波重力观测信息,不建议直接用于更小尺度的地质和地球物理解释. 相似文献
7.
Yves Bernabé 《Physics of the Earth and Planetary Interiors》1981,27(2):151-157
Following a pre-existing mathematical model, a mathematical assumption of linearity is used to compute isostatic anomalies directly from geodetic and gravimetric data. When applied to the Rhine graben, this method yields satisfactory results which justify it a posteriori. The computation of a model of the distribution of compensation masses inside the Earth necessitates further mathematical assumptions which make the results physically questionable. 相似文献
8.
重力空白区数据填补的一个主要方法是基于地壳均衡理论进行的,该方法亦用于EGM系列模型的构建中.本文研究了地形数据在构制地形/均衡重力场模型中的应用,分析了补偿深度对Airy位模型和面凝聚位模型的影响,给出二者的最佳补偿深度分别为50 km和40 km.以纯卫星重力模型为参考,后者在前120阶的精度要高于前者,但在121~250阶的精度较低,组合模型精度高于单一模型精度.对地形/均衡地球重力场模型进行了EGM2008拟稳分析,研究了不同分辨率基准的拟稳效果,分析表明：30'分辨率的拟稳基准所得拟稳模型对应的阶方差与参考阶方差曲线直到360阶都有较好的一致性,以EGM2008为基准,其相对累计大地水准面高误差在140阶时为6.83cm,相对累计重力异常误差在220阶时为1.10 mGal. 相似文献
9.
本文基于Vening Meinesz区域均衡模型,通过试验不同参数计算Vening Meinesz均衡补偿深度,将其与CRUST1.0模型给出的莫霍面深度进行拟合,得到适应于天山及邻区的平均补偿深度、"地区性指标"以及区域补偿半径.结合地球重力场模型EIGEN-6C4与地形数据,利用球冠体积分方法进行地形效应、沉积层效应计算和均衡校正,得到了研究区的Vening Meinesz均衡重力异常.结果显示天山及邻区的均衡重力异常幅值在-110~120 mGal之间,表明了天山及周边盆地岩石圈所处于的均衡状态,同时揭示了研究区的壳幔密度分布特征.天山、塔里木盆地、准噶尔盆地等块体的地壳垂向形变可能部分地由均衡调整引起,且均衡调整趋势与地面形变测量结果相契合.通过对均衡重力异常成因的解释,从地壳均衡角度分析了该地区复杂的构造背景及其新生代以来的演化历程. 相似文献
10.
均衡状态是评价一个地区现今地壳构造活动性的一个重要标志。本文通过对东北南部地区普拉特—海福特均衡重力异常特征的分析,并通过均衡重力异常与深部地壳测深结果、地形趋势面自由空气重力异常以及与艾理均衡重力异常结果的对比分析,以达到:(1)为研究者提供一些基础资料;(2)通过对比分析,进一步了解东北南部地区及海城震区的均衡状态,以期在海城震区深部地球物理特征的研究方面获得进展。 相似文献
11.
Rui Feng Jun Wang Shuzhen Zheng Guifang Huang Huifen Yan Hainan Zhou Ruoshui Zhang 《地震学报(英文版)》1988,1(4):73-84
Following Airy and Pratt principles, five kinds of local-compensation models are analysed and a rapid 3-D gravity formula
is utilized to calculate isostatic anomalies for 66 models with different parameters. It is noted that isostatic gravity maps
appear nearly identical in their main patterns and features. The optimum compensation model in North China is one of modified
Airy models in which the different density distribution in the surface, upper crust and lower crust is taken into account
and the standard crustal thickness is about 50km. The position of the complete compensation interface is located in the upper
mantle. The North China platform as a whole is under sub-isostatic equilibrium status with an isostatic anomaly of about 18·10−5 m/s2 on an average. The distribution of isostatic gravity anomaly shows an obvious blockwise pattern. Most positive anomaly areas
occur over the eastern part, the Jiao-Liao Block, Mt. Yan block and northern margin of the Hebei-Shandong block, whereas a
negative area occurs in the Shanxi graben. The comparison of models indicates that the Moho discontinuity is not suitable
to be taken as a compensation interface, and the compensation effects in Airy model are better than that in Pratt model, which
is consistent with the feature of dominant layered structure and less lateral inhomogeneity in crust. Some results about composite
compensation, the basic characteristics of isostatic anomaly and deep stucture will be published later in the second part
of this paper.
Wang Bowen took part in some work in this paper. 相似文献
12.
Rui Feng Jun Wang Shuzhen Zheng Guifang Huang Huifen Yan Hainan Zhou Ruoshui Zhang 《地震科学（英文版）》1988,1(4):73-84
Following Airy and Pratt principles, five kinds of local-compensation models are analysed and a rapid 3-D gravity formula is utilized to calculate isostatic anomalies for 66 models with different parameters. It is noted that isostatic gravity maps appear nearly identical in their main patterns and features. The optimum compensation model in North China is one of modified Airy models in which the different density distribution in the surface, upper crust and lower crust is taken into account and the standard crustal thickness is about 50km. The position of the complete compensation interface is located in the upper mantle. The North China platform as a whole is under sub-isostatic equilibrium status with an isostatic anomaly of about 18·10?5 m/s2 on an average. The distribution of isostatic gravity anomaly shows an obvious blockwise pattern. Most positive anomaly areas occur over the eastern part, the Jiao-Liao Block, Mt. Yan block and northern margin of the Hebei-Shandong block, whereas a negative area occurs in the Shanxi graben. The comparison of models indicates that the Moho discontinuity is not suitable to be taken as a compensation interface, and the compensation effects in Airy model are better than that in Pratt model, which is consistent with the feature of dominant layered structure and less lateral inhomogeneity in crust. Some results about composite compensation, the basic characteristics of isostatic anomaly and deep stucture will be published later in the second part of this paper. 相似文献
13.
The availability of digital elevation databases representing the topographic and bathymetric relief with global homogeneous coverage and increasing resolution permits the computation of crust-related Earth gravity models, the so-called topographic/isostatic Earth gravity models (henceforth T/I models). Although expressing the spherical harmonic content of the topographic masses, the interpretation purpose of T/I models has not been given the attention it deserves, apart from the fact that they express some degree of compensation to the observed spectrum of the topographic heights, depending on the kind of the applied compensation mechanism. The present contribution attempts to improve the interpretation aspects of T/I Earth gravity models. To this end, a rigorous spectral assessment is performed to a standard Airy/Heiskanen T/I model against different CHAllenging Minisatellite Payload (CHAMP), Gravity Recovery and Climate Experiment (GRACE), Gravity field and steadystate Ocean Circulation Explorer (GOCE) satellite-only, and combined gravity models. Different correlation bandwidths emerge for these four groups of satellite-based gravity models. The band-limited forward computation of the models using these bandwidths reproduces nicely the main features of the applied T/I model. 相似文献
14.
As part of the resource evaluation and exploration program conducted by Los Alamos Scientific Laboratory for the national Hot Dry Rock (HDR) Geothermal Program, a regional magnetotelluric (MT) survey of New Mexico and Arizona is being performed. The MT lines are being located in areas where the results of analysis of residual gravity anomaly maps of Arizona and New Mexico, integrated with other geologic and geophysical studies indicate the greatest potential for HDR resources.The residual gravity anomalies are derived by applying the concept of predicting gravity anomalies from topography. This can be accomplished by employing reductions similar to those used in some isostatic investigations, in which a regional topographic surface is used as the Bouguer reduction datum. The datum is derived by comparison of various harmonics of Bouguer anomalies and elevations of stations. Topography can be used to predict Bouguer anomalies because of isostatic compensation; the resultant anomalies can be considered high frequency residual anomalies or isostatic anomalies corrected for regional compensation. Such maps have been produced for Arizona, New Mexico, west Texas, and Chihuahua, Mexico.The main objective of the MT project is to produce a regional geoelectric contour map of the pervasive deep electrical conductor within the crust and/or upper mantle beneath the Colorado Plateau and the adjacent Basin and Range Province and Rio Grande Rift. The MT survey consists of 200 sites along several long profiles with site spacing of 15–20 km. Pre-existing available MT data are being integrated with the new data. After the data are processed, a one-dimensional inversion is applied to the sounding curve and used as a starting point for 2-D modeling. Such a project and ultimate map will be of major value in studying the regional geophysics and tectonics of the southwest United States as they now apply to HDR resources in particular and geothermal resources in general.Electrical conductivity anomalies of large areal extent are of particular interest in geothermal exploration. Correlation analysis of large conductive anomalies with other geophysical, geological, and geotectonic data is being performed. Preliminary analysis of the data has suggested several major regions of anomalously shallow high electrical conductivity. Among these is the Aquarius area of northwest Arizona which is the site of a longwavelength residual anomaly low, which when modeled and correlated with other geophysical data can be shown to be possibly related to low density and high temperature in the crust at depths of 20 km or less. Preliminary analysis of MT data indicates the possible existence of a mid-crustal high electrical conductivity anomaly in this same region. 相似文献
15.
Annie Souriau 《Earth and Planetary Science Letters》1984,68(1):101-114
Gorringe Ridge is a strong uplifted block of oceanic crust and upper mantle lying at the eastern end of the Azores-Gibraltar plate boundary. The geoid over this structure derived from Seasat altimeter data exhibits a 9-m height anomaly with a north-south lateral extension smaller than 200 km. An attempt is made to interpret this geoid together with the gravity anomalies and with the seismicity, which has been compiled as a function of depth.It is first shown that the flexure of the oceanic lithosphere due to the ridge loading does not provide a good fit of the geoid anomalies and probably should be discarded, as it assumes a continuous unfractured elastic plate.Models involving local heterogeneities are then tested. The comparison of the observed geoid anomalies with the anomalies due to the uncompensated relief indicates that the topographic high has no shallow compensation.Uncompensated models, previously proposed to explain the gravity anomalies, are tested using the geoid. One model (Purdy and Bonnin, in Bonnin [11]), which involves an uplift of upper mantle material at depth, generates too strong geoid anomalies and must be discarded. Another model, which represents a nascent subduction zone (Le Pichon et al. [25]), fits both the gravity and geoid anomalies, but leads to difficulties in explaining the deep seismicity north of Gorringe Ridge.A model in isostatic equilibrium is also able to fit both gravity and geoid anomalies. This model involves a deep root of density 3.0 g cm?3, as has been previously proposed for many oceanic ridges and plateaus. This model is compatible with the deep seismicity, but the origin of this low-density material at great depth is up to now an unresolved question.More likely, dynamical models taking into account the forces induced by the convection related to the slow plate convergence in this area will have to be considered. 相似文献
16.
Lars E. Sj?berg 《Studia Geophysica et Geodaetica》2012,56(4):929-933
Recently it was proved that the classical formula for computing the geoid to quasigeoid separation (GQS) by the Bouguer gravity anomaly needs a topographic correction. Here we generalize the modelling of the GQS not only to Bouguer types of anomalies, but also to arbitrary reductions of topographic gravity. Of particular interest for practical applications should be isostatic and Helmert types of reductions, which provide smaller and smoother components, more suitable for interpolation and calculation, than the Bouguer reduction. 相似文献
17.
根据经典均衡的原理,本文重点分析了五种局部均衡补偿模式.在计算方法上利用频域三维重力场的理论公式,快速求得均衡校正值,据此计算了66个模型的均衡重力异常场,注意到对这许多不同参量的模型而言,它们的均衡异常场在形态与分布特征上基本一致,其中计入了地表和上下地壳密度差异分布的 Airy 模型具有最佳的补偿效果,它的均衡面在莫霍界面以下的上地幔中,标准深度50km.从整体上看,华北地台处于亚均衡状态,均衡异常的均值为1810-5m/s2.均衡重力异常的分布表现出明显的块体特征,正均衡异常区主要分布在东部胶辽地块和冀中平原北缘,在汾渭裂谷区存在负异常.模型对比表明,以莫霍界面作为均衡补偿面的模型是不可取的;Airy 模型比 Pratt 模型的补偿效果略好,这同地壳构造以层状为主而侧向变化有限的特征相符.有关复合补偿、均衡重力异常的基本特征和深部构造的关系等结果,将在文章的第二部分发表. 相似文献
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20.
M.E. ArtemjevV.I. Bune V.A. DubrovskyN.Sh. Kambarov 《Physics of the Earth and Planetary Interiors》1972,6(4):256-262
Both a theoretical treatment and observed data show that the isostatic gravity field and the seismicity are closely related. The equation for harmonic loading shows that large deviations from isostatic equilibrium lead to large shear stresses in the crust. High seismic activity correlates well with large isostatic gravity anomalies and with large horizontal gradients of isostatic gravity anomalies. Studies of seismicity should consider the isostatic gravity field. 相似文献