共查询到20条相似文献，搜索用时 140 毫秒
1.
利用重力异常揭示地壳三维密度结构是重力资料地质解释的目标和任务,密度反演的好坏至关重要.本文对华北克拉通进行了重力异常多尺度密度反演研究,首先利用小波变换对重力异常进行多尺度分解,接着利用功率谱分析方法估算各层场源的平均深度,然后利用广义密度反演方法进行各层密度反演,对华北地区进行了多层密度反演,得到其密度结构,并进行地质解释和油气藏分析.结果显示了重力场多尺度密度反演方法的有效性,对华北地区密度结构的地质含义进行了初步分析,位于造山带中的低密度异常主要反映沿造山带展布的花岗岩体.对比华北东部区浅层密度扰动与油气坳陷位置,发现油气坳陷都表现为低幅度的低密度异常区.说明利用小波多尺度反演提取的密度信息对油气勘探的部署有一定指导意义. 相似文献
2.
显生宙以来华北克拉通岩石圈遭到破坏,这一现象的科学问题已受到世界地学家广泛关注.本文首先将地震层析成像反演得到的P波速度扰动转化为密度扰动,以此作为初始密度模型,然后利用布格重力异常反演得到了华北克拉通岩石圈高分辨三维密度结构.为了避开大型稀疏矩阵求逆计算,提高计算效率,我们将代数重构技术用于密度反演解算.反演结果表明:华北克拉通岩石圈密度在横向和纵向上均存在明显的不均匀性,密度分布形态与地表构造格局有很好的相关性;研究区地壳整体表现为低密度异常,地壳以下岩石圈部分则以高密度异常为主;鄂尔多斯块体地壳范围内以低密度异常为主,80~120 km深度上为呈南北两端集中分布的高密度异常,并分别与秦岭造山带和阴山造山带的高密度异常分布相连,这暗示了鄂尔多斯块体可能受到了来自其南北两端造山带深部动力学过程的影响;80~120 km深度上,华北克拉通东部地区呈现出显著的南北向非均匀的高密度异常,这表明遭到破坏后该地区上地幔物质分布具有强烈的南北向非均匀性. 相似文献
3.
Vinton dome地区位于美国墨西哥湾,发育着大量的盐丘构造,为油气的储藏创造了有利条件.地震勘探结果在盐丘区域存在一定的发散从而难以准确地确定盐丘的准确范围,难以为钻探工作提供可靠的信息.为了获得准确的盐丘形态,现今大多采用重力与地震数据的联合解释.重力梯度异常相对原始重力异常具有更高的分辨率,Bell Geospace公司于2011-2012年在Vinton地区进行了全张量重力测量.本文推导出重力张量异常进行界面正反演的公式,并通过理论模型试验证明了重力与张量异常联合反演可有有效地提高反演结果的准确性.根据先前地震结果利用实测重力张量异常反演获得了Vinton dome地区盐丘界面的变化,此外还利用密度反演方法圈定出盐丘的具体分布,结果显示两种方法所获得的盐丘顶面位置相一致,从而为下一步的钻探工作提供了有力的保障. 相似文献
4.
密度界面反演作为了解地球内部结构的一种重要方法,长期以来都是重力学研究的主要内容.本文结合抛物线密度模型及频率域算法的优点,将抛物线密度函数应用于Parker-Oldenburg算法,经过理论推导得到了抛物线密度模型的频率域公式,从而建立了基于抛物线密度模型的三维密度界面重力异常正反演的算法和流程.理论模型数据试验表明本方法快速、有效,适用于大多数浅部比深部增加更快的实际地壳密度.研究中还利用该方法对川滇地区重力异常进行了反演,获得了该区的莫霍面深度分布,并与接收函数研究结果进行对比分析,进一步验证了本文方法的正确性和有效性. 相似文献
5.
在阻尼最小二乘法的基础上,提出了利用重力进行三维密度反演的选权拟合法,并利用密度分布的特点构造了约束权矩阵.为了改善单一重力反演的非唯一性,利用地震面波层析成像资料进行约束,得到了青藏高原不同深度高分辨率三维密度异常分布图.反演结果显示,青藏高原地壳内密度很不均匀,不同块体具有不同的密度异常特征,拉萨和羌塘地体为低的负密度异常区,松潘-甘孜地体东部存在较低的负密度异常区,塔里木盆地存在较高的正密度异常区.从中部到东部,上地壳物质存在差异,而下地壳物质存在一定连续性. 相似文献
6.
综合重力观测资料和地震波走时资料反演了青藏高原东北缘岩石圈三维密度结构,并对该区岩石圈结构及动力学特征进行了讨论.首先利用收集到的P波近震和远震走时数据进行地震层析成像,得到研究区岩石圈三维P波速度结构.然后利用速度-密度经验关系式,将速度扰动转化为密度扰动建立研究区三维初始密度模型.最后利用分离的布格重力异常反演得到了岩石圈三维密度结构.反演结果表明:青藏高原东北缘地壳密度结构特征有利于地震孕育发生和地壳物质侧向流动;地壳内,密度异常等值线走向与地表断裂走向基本一致,进入地幔后,密度异常等值线走向发生了顺时针旋转,这表明青藏高原东北缘地壳和地幔具有不同的构造运动模式,暗示该区可能发生了壳幔解耦;80~100 km深度上,P波速度异常较密度异常明显偏低,推测该区可能发生了部分熔融或者岩石含水量的增加;印度板块俯冲和周围坚硬块体阻挡联合作用,使得青藏高原东北缘形成了强大的区域构造应力场,并导致深部软流圈热物质上涌,为该区壳幔解耦、部分熔融和P波速度降低创造了条件. 相似文献
7.
本文利用Extrapolation Tikhonov正则化算法处理重力梯度数据三维密度反演的线性不适定问题。与Tikhonov正则化方法相比,Extrapolation Tikhonov正则化方法减小了因正则化参数的引入而带来的反演结果误差,提高了预测数据与观测数据之间的拟合精度。同时为了消除位场数据反演时位置函数快速衰减对反演结果的影响,本文提出了基于重力梯度全张量特征向量法的深度加权函数,模型试验证明了该深度加权函数能有效识别异常体密度分布特征。对澳大利亚Kauring地区实测重力梯度数据进行反演,并和已有研究成果对比分析。结果表明该反演方法能够较好的获取地下异常体的密度分布信息。 相似文献
8.
讨论了利用面波与布格重力异常联合反演三维地壳速度结构的新方法,并利用该方法联合反演获得山西断陷带地壳S波速度结构.通过建立速度与密度之间的经验关系,利用非线性迭代反演方法获得最终速度模型.结果显示,联合反演获得的速度模型可以同时提高对面波及重力数据的观测拟合程度,而面波单独反演得到的速度模型则无法很好的拟合重力观测数据.相比较,联合反演速度模型中的大同火山区中下地壳的低速异常幅值小于面波单独反演模型中低速异常体的幅值.联合反演速度模型结果揭示,吕梁山地区在中下地壳存在低速异常,并且和北部的大同火山区低速异常相连接,说明可能导致新生代以来大同火山区岩浆活动的上地幔构造活动(上地幔局部上涌,地幔柱)可能对山西断陷带的形成和构造活动起到了一定的控制作用,并且导致了吕梁山地区中下地壳的低速异常. 相似文献
9.
重力异常揭示地壳三维密度结构是地球物理的重要目标和任务,其关键技术是密度反演.本文对滇西地区重力异常进行了多尺度密度反演,首先利用小波变换对重力异常进行多尺度分解,接着利用功率谱分析方法估算各层场源的平均深度,然后利用广义密度反演方法进行各层密度反演,取得区域地壳多个深度上的密度扰动图像.滇西上地壳高密度扰动出现在扬子克拉通内部和西缘,以及澜沧江断裂带西缘,后者对应昌宁—勐连蛇绿混杂岩带及岛弧岩浆岩带.上地壳低密度异常主要反映西昌裂谷带和高黎贡—腾冲一带的岩浆房,和兰坪—思茅盆地中的坳陷带指示钾盐等沉积矿产目的层较厚的区段.滇西上地壳和中地壳出现三条低密度扰动带,与三期大陆碰撞带的吻合.大部分6级以上地震分布在低密度异常区或它们的边缘,只有在西昌—元古谋裂带才分布在高密度异常区.克拉通内部古裂谷带地震可分布在高密度异常区.在26°N线以南下地壳为高密度区,以北为低密度区.因此,26°N线的一个属性是下地壳密度差异分界线.滇西由北向南地壳加厚缩短的程度是逐渐变弱的,在26°N线以南,南北向的地壳加厚缩短就不明显了.高黎贡走滑剪切带、澜沧江走滑剪切带、红河走滑剪切带在滇西中地壳密度扰动平面图中表现为密度急变的梯度带.表明这三条主要的走滑剪切断裂带都穿过中地壳并可能延深到下地壳. 相似文献
10.
在波数域中用重力反演莫霍面深度时通常假定壳幔密度差为一常数,但这只是一种近似的密度模型,本文采用了密度随深度呈指数变化的变密度模型来反演莫霍面深度,给出了利用指数密度模型在波数域中计算重力异常的正演公式及界面深度的反演公式.利用指数密度模型及重力资料反演了青藏高原莫霍面的深度,分析了莫霍面的特征.结果表明,青藏高原莫霍面呈现出边缘浅、中部深的特点,边缘变化快、梯度大,中间变化梯度趋缓.中心地带的羌塘地体莫霍面深度达74 km,向四周慢慢变浅至67 km左右,边缘地区突然变浅至50km左右.通过常密度模型、变密度模型及地震反演得到的莫霍面的比较,证实变密度模型更适合于莫霍面结构的反演. 相似文献
11.
Recently observed features in the subsurface geology of the Haifa Bay area (northern Israel) have been evaluated using 3-D forward gravity and magnetic modeling and inversion schemes. The interpretation is based on updated petrophysical data of the Jurassic, Cretaceous and Tertiary sedimentary layers and volcanics. It has been shown that the Bouguer gravity anomalies correspond mainly to thickness variations in the Senonian to Tertiary sediments. The gravity effect of these sediments was calculated using their actual densities and structural setting as interpreted from seismic reflection data. This effect was removed from the Bouguer gravity in order to study the pre-Senonian geological structures. The pattern of residual gravity anomalies (named “stripped gravity”) is essentially different from the pattern of the Bouguer gravity. The prominent Carmel gravity high, clearly seen on the Bouguer gravity map, completely vanishes on the “stripped” gravity map. That suggests that this relatively positive anomaly is caused by the considerable thickness of the low-density young sediments in the surrounding areas and does not correspond to high-density magmatic rocks or crystalline basement uplift as previously suggested. The average densities of the Jurassic and Cretaceous volcanics are generally lower then those of the background sedimentary rocks. Volcanics are the main cause for magnetic anomalies onshore and offshore northern Israel. The magmatic root of the Asher volcanics is, most probably, located close to the Yagur fault. A large, deep-seated gabbroic intrusion is assumed to be located under the Mediterranean abyssal plain in the NW part of the study area. The Atlit marine gravity low appears to be caused by a thick Mesozoic and Tertiary sedimentary accumulation. The results presented should be of considerable assistance in delineating some aspects of hydrocarbon exploration in the area. 相似文献
12.
基于布格重力异常相对于地形起伏光滑分布的约束条件,从一维自由空气重力异常数据出发,采用贝叶斯方法估算近地表岩石密度,同时采用三次B样条函数拟合布格重力异常,获取光滑分布的布格重力异常.数据拟合和光滑约束之间的权重采用Akaike贝叶斯准则(ABIC准则)自动确定.均匀剖分模型和不均匀剖分模型数据试验都验证了该方法的有效性.相关参数评价表明,足够多的样条系数可以提高估计结果的准确性,样条系数的个数接近测点数时可获得较稳定的估计结果.增大异常的噪声水平时,ABIC准则可有效地自动增大先验光滑约束的权重.云南地区两条重力剖面应用结果表明,剖面沿线的近地表密度值起伏变化明显(达2.45~2.8g·cm^-3),前寒武纪和古生代地层密度相对较高(主要为2.53~2.75g·cm^-3),而中生代密度较低(2.45~2.73g·cm^-3);本文估计的近地表密度结果与区域物性资料及地表地质特征较吻合;估计的剖面布格重力异常具有光滑性;红河断裂两侧近地表密度差异较大,可达0.4g·cm^-3.本文获得的两条剖面近地表密度结构和布格重力异常为该区深部结构与构造研究提供更可靠的重力基础数据. 相似文献
13.
14.
Some aspects of the analytical procedure for an automatic fitting of gravity and magnetic anomalies are discussed. An example of application relative to the Campania volcanic district near Naples, Italy, is reported. Gravity anomalies in that area mainly reflect the depth to the carbonate basement rocks. A small gravity high over Vesuvius may indicate buried volcanic layers. Magnetic anomalies near L. Patria and Castel Volturno are interpreted to be caused by buried intrusive rocks of higher susceptibility. Computer models of subsurface rock units with appropriate densities and susceptibilities have been generated to match the observed anomalies. 相似文献
15.
—Methods and the results of estimating the anomalies characterising the density inhomo geneities in the European-Mediterranean upper mantle are described. These anomalies were obtained by subtracting the gravity effect of a crustal density model derived from seismic velocities from the observed gravity field averaging over an area of 1°× 1°. The 3-D density model of the study region comprises two regional layers of varying thickness with lateral variation of average density the sedimentary cover and the crystalline crust. The average densities for model layers were evaluated by using a velocity/density conversion function and taking into account sediment consolidation with depth. Clear correlation between residual gravity anomalies and both velocity heterogeneities and thermal regime data of the upper mantle has been revealed. An agreement of positive anomalies over the Alps, the Adriatic plate and the Calabrian Arc with high velocity domains in the upper mantle and reduced temperatures at the subcrustal layer are caused by lithospheric "roots" and thickened lithosphere below these structures. Gravity residual lows, revealed over the Western Mediterranean Basin and Pannonian Basin, are in correspondence with both low velocities and high temperatures in the upper mantle. These anomalies are the result of the presence of asthenosphere in shallow near-Moho depths below these basins. 相似文献
16.
本文利用GOCEL2观测重力梯度的五个独立分量(T_(xx),T_(zz),T_(xy),T_(xz),T_(yz)),联合EGM2008地球重力场模型计算垂直重力,反演计算了青藏高原及邻区0~120 km深度岩石圈三维密度结构.将经过低阶项改正、地形效应改正、沉积层界面起伏效应改正得到的剩余重力及重力梯度异常值作为观测值,以改正剩余量归一化权重作为观测权重,基于Tikhonov正则化理论建立反演目标函数.反演过程中,利用地震层析S波速度转换密度作为初始约束,通过非等权最小二乘迭代法计算得到最终反演密度.反演结果表明:(1)40 km深度,青藏高原内部为中地壳,表现为低密度,邻区为中下地壳,表现为高密度.青藏高原内部中地壳强低密度层主要分布在高原边界.其成因是印度板块俯冲和周围坚硬块体阻挡作用导致在高原边界形成的高应变积累闭锁区,为壳内低密度软弱物质的形成提供了条件.(2)80 km深度,青藏高原上地幔顶部显示出低密度的特征.高原内部东、中、西密度特征差异明显,低密度以95°E为中心线呈东西对称分布.以班公一怒江缝合带为中心,在拉萨块体和羌塘块体内从北向南出现了"低-高-低"的密度分布起伏特征.该特征与GRACE得到的莫霍面起伏特征一致,结合大地构造结果,这种起伏特征验证了印度、羌塘块体从南北两侧分别向喜马拉雅、拉萨地块挤入的双向俯冲模式.(3)四川盆地和鄂尔多斯盆地内,地壳高密度异常较地震波速异常明显偏低,表明古老的四川盆地和鄂尔多斯盆地比想象中更冷、更坚硬.塔里木盆地和柴达木盆地内壳、幔高密度的结构特征,对应地幔物质上涌. 相似文献
17.
地质体的重力建模是正确解释和应用重力资料的关键问题之一.针对非规则形状变密度的三度体,本文提出了基于3D Delaunay剖分算法的重力建模方法.采用3D Delaunay剖分算法将三维目标地质体分解为若干变密度四面体体元,推导了基于四面体体元的重力正演公式,建立了剩余密度值与重力异常值的线性方程组;以变密度的长方体和倾斜台阶组合体为例,比较分析了常规块体算法和3D Delaunay剖分算法应用于重力正演的有效性,并采用共轭梯度法加密度约束条件对非规则形状变密度的倾斜台阶组合体进行了密度反演.计算结果验证了本文方法的正确性和有效性.基于3D Delaunay剖分算法的重力建模可应用于存在褶皱、断层、裂缝等复杂地质体的重力正反演计算. 相似文献
18.
Constraints in 3D gravity inversion 总被引：5，自引：0，他引：5
A three-dimensional (3D) inversion program is developed to interpret gravity data using a selection of constraints. This selection includes minimum distance, flatness, smoothness and compactness constraints, which can be combined using a Lagrangian formulation. A multigrid technique is also implemented to resolve separately large and short gravity wavelengths. The subsurface in the survey area is divided into rectangular prismatic blocks and the problem is solved by calculating the model parameters, i.e. the densities of each block. Weights are given to each block depending on depth, a priori information on density and the density range allowed for the region under investigation. The present computer code is tested on modelled data for a dipping dike and multiple bodies. Results combining different constraints and a weight depending on depth are shown for the dipping dike. The advantages and behaviour of each method are compared in the 3D reconstruction. Recovery of geometry (depth, size) and density distribution of the original model is dependent on the set of constraints used. From experimentation, the best combination of constraints for multiple bodies seems to be flatness and a minimum volume for the multiple bodies. The inversion method is tested on real gravity data from the Rouyn-Noranda (Quebec) mining camp. The 3D inversion model for the first 10 km is in agreement with the known major lithological contacts at the surface; it enables the determination of the geometry of plutons and intrusive rocks at depth. 相似文献
19.
Mean free-air gravity anomalies are often needed in geodesy for gravity field modelling. Two possible ways of compiling the mean free-air gravity anomalies are discussed. One way is via simple Bouguer gravity anomalies and the second and more time consuming way is via refined Bouguer gravity anomalies. In flat areas the differences between using any of the two ways should not be significant. In the mountains however, every effect introducing a high dependency, such as e.g. terrain effect, can negatively affect the interpolation process. In fact, a numerical experiment conducted in one part of Rocky Mountains revealed large and systematic differences. The effect of these differences on the geoid model is more then two meters in the test area. Our investigation shows that this bias is caused by the location of gravity measurement points, chosen mostly on hill-tops. At such points, the terrain correction to gravity is systematically larger than the mean value of the correction. Therefore, it is not possible to prevent the mean free-air gravity anomalies obtained from simple Bouguer gravity anomalies from having a systematic bias. One can see this bias as a result of the aliasing effect because the simple Bouguer gravity anomalies in the mountains contain a higher frequency signal (terrain effect) that is, according to sampling theorem, impossible to reconstruct by sparse measured gravity data, see e.g. (Goos et al., 2003). Therefore, the more rigorous way of computing the mean free-air gravity anomalies is via refined Bouguer gravity anomalies. 相似文献