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Carla Braitenberg Jörg EbbingHans-Jürgen Götze 《Earth and Planetary Science Letters》2002,202(2):387-404
An unconventional scheme is used to estimate the flexural rigidity, or equivalently the elastic thickness of the lithosphere, given the topography and gravity data. The flexural rigidity is the parameter that governs the flexural response of the lithosphere in the frame of the thin plate flexure model. The scheme is an alternative to the widely used calculation of admittance of topography (sea-floor or continental topography) and gravity, bearing some advantages which are explained in the paper. The scheme involves the inversion of the gravity data in order to formulate a model of the crust-mantle interface (CMI) undulations. In a second step the flexure parameter is then evaluated from the relation between topography and CMI variations. Instead of calculating the admittance function using a spectral analysis, a set of point-load response functions are used in order to retrieve the optimal flexure parameter. This has two main advantages: instabilities of the numerical admittance evaluation at wavenumbers with low spectral energy in the topography are overcome and the analysis can be made over an area which is not necessarily rectangular, as required for the spectral analysis. The proposed method allows a higher space resolution of elastic thickness than any spectral method. For validation, the numerical strategy is applied to the situation of a realistic synthetic model, where all inputs and outputs are known a priori. Finally the spatial variations of the elastic thickness are studied in an area across the Eastern Alps. 相似文献
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本文利用EIGEN-6C4重力数据和ETOPO1地形数据,在考虑物质密度横向不均匀的情况下,在东北亚地区展开地壳均衡研究,并重点分析了长白山的隆升机制.首先,针对穿越长白山和库页岛的两条近乎东西向的剖面（剖面A、B）展开详细研究,以CRUST1.0模型为初始条件,利用布格重力异常数据,基于Airy模型和Airy-Pratt模型分别反演了相应剖面的地壳密度结构,发现两剖面的地壳密度呈现一定程度的横向不均匀特性;接着基于上述密度结构和高程数据,利用Airy均衡理论计算了相应剖面的均衡面深度,并进一步比较莫霍面（Moho）和均衡面的差异,计算了剖面的垂向构造应力分布;然后,把上述方法应用到整个东北亚地区,计算了1°采样的21条东西向剖面的垂向构造应力,插值得到整个东北亚地区的垂向构造应力分布.结果表明,东北亚大部分地区垂向构造应力基本为零,总体处于均衡状态,长白山地区垂向构造应力为-15~-25 MPa,日本列岛垂向构造应力为-40~-50 MPa,太平洋海沟垂向构造应力为15~25 MPa;最后,本文运用自由空气重力异常导纳方法,计算了长白山地区的有效弹性厚度（Te）和加载比,发现长白山地区的Te为10 km,表明该地区的岩石圈较为柔软;加载比结果显示,岩石圈初始加载主要来自莫霍面,占总加载的78%,表明长白山的隆升主要源自地幔物质上涌. 相似文献
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Geophysical models for the tectonic framework of the Lake Vostok region, East Antarctica 总被引：2，自引：0，他引：2
Michael Studinger Garry D Karner Vadim Levin Anahita A. Tikku 《Earth and Planetary Science Letters》2003,216(4):663-677
Aerogeophysical and seismological data from a geophysical survey in the interior of East Antarctica were used to develop a conceptual tectonic model for the Lake Vostok region. The model is constrained using three independent data sets: magnetic, seismic, and gravimetric. A distinct change in the aeromagnetic anomaly character across Lake Vostok defines a crustal boundary. Depth to magnetic basement estimates image a 400-km-wide and more than 10-km-deep sedimentary basin west of the lake. Analysis of teleseismic earthquakes suggests a relatively thin crust beneath Lake Vostok consistent with predictions from kinematic and flexural gravity modelling. Magnetic, gravity, and subglacial topography data reveal a tectonic boundary within East Antarctica. Based on our kinematic and flexural gravity modelling, this tectonic boundary appears to be the result of thrust sheet emplacement onto an earlier passive continental margin. No data presently exist to date directly either the timing of passive margin formation or the subsequent shortening phase. The preserved thrust sheet thickness is related to the thickness of the passive margin crust. Because a significant amount of time is required to erode the thrust sheet topography, we suggest that these tectonic events are Proterozoic in age. Minor normal reactivation of the thrust sheet offers a simple mechanism to explain the formation of the Lake Vostok Basin. A low level of seismicity exists in the vicinity of this tectonic boundary. The existence of a crustal boundary in the Antarctic interior provides new constraints on the Proterozoic architecture of the East Antarctic craton. 相似文献
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青藏高原作为中国大陆强震活动的主体区,不但构造变形历史复杂,而且高原内部与周边块体之间的重力异常差异也十分显著。本文基于EGM2008重力模型,计算得到了青藏高原及周边地区的区域布格重力异常和艾里均衡重力异常;并依据复合均衡模型原理,以Crust1.0地壳模型中莫霍面的深度为参考,反演得到了地壳剩余密度的分布,该结果适用于研究地壳横向密度的差异;最后,将反演结果与弹性板均衡理论模型反演得到的岩石层有效弹性厚度进行对比,结果表明,青藏高原与周边地块之间的地壳力学特性和平均密度存在显著差异,为强震孕育提供了动力学背景。以此为依据,可为潜在强震危险区位置的判断提供参考。 相似文献
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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
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《Journal of Geodynamics》2010,49(3-5):284-291
The island of Taiwan is located on the convergent boundary between the Philippine Sea plate and the Chinese continental margin. It offers very active mountain building and collapsing processes well illustrated by the rugged topography, rapid uplift and denudation, young tectonic landforms, active faulting and numerous earthquakes. In this paper, using simple models, we have estimated vertical movements and associated absolute gravity variations which can be expected along a profile crossing the southern part of the island and probably suffering the highest rates of rising. The two different tectonic styles proposed for the island, thin-skinned and thick-skinned, were taken into account. Horizontal and vertical movements were modeled by an elastic deformation code. Gravity variations due to these deformations are then modeled at a second step. They are dominated by plate and free-air effects, i.e. elevation of the topography, with several μGal yr−1. By comparison, gravity changes generated by mass transfers are weak: maximum 0.1 μGal yr−1 with the thin-skinned tectonic and 0.3 μGal yr−1 with the thick-skinned tectonic. Though elastic rheology has limitations, this modeling offers interesting results on what gravity signal can be expected from the AGTO project (Absolute Gravity in the Taiwanese Orogen), which proposes to study the dynamic of these mountain ranges using absolute gravimetry (AG) and also including relative gravimetry (RG) and GPS measurements. 相似文献
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本文以地质与地球物理资料作为约束条件,利用小波多尺度分析方法,对首都圈地区重力场进行了有效分离,应用Parker位场界面反演法及变密度模型对莫霍界面进行了反演分析,并构建了两条地壳密度结构剖面模型,对该区精细地壳结构进行了深入研究.研究结果表明首都圈地区受多期构造运动的改造,形成坳、隆相邻,盆、山相间,密度非均匀性,壳内结构与莫霍面埋深相差比较大的地壳分块构造格局.受华北克拉通岩石圈伸展、减薄以及岩浆的上涌底侵作用,首都圈地区莫霍面起伏比较大,莫霍面区域构造方向呈NE-NNE方向,在盆地向太行山、燕山过渡地带形成了莫霍面陡变带;盆地内部莫霍面形成东西向排列、高低起伏的框架,最大起伏约5 km,但平均地壳厚度比较小,北京、唐山地区地壳厚度最小约29 km,武清凹陷地壳厚度最大约34 km.在重力均衡调整作用下,西部太行山区地壳厚度较大,但地壳密度小于华北裂谷盆地内部;中上地壳重力场特征与地表地形及地貌特征具有很大的相关性.受新生代裂谷作用影响,首都圈中上地壳结构非常复杂,形成了NNE方向为主体的构造单元,断层多下延至中地壳;下地壳发生明显的褶曲构造,表现出高低密度异常相间排列的典型特征;首都圈地区地壳密度具有明显的非均匀性.研究认为首都圈地区地震的发生与上地幔顶部及软流层物质的上涌有一定关系. 相似文献
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华北克拉通中东部基底构造单元的重磁特征 总被引：10，自引：2，他引：8
系统收集并重新处理了华北克拉通中东部的重磁资料,利用处理结果,结合近年来华北克拉通前寒武纪结晶基底构造研究的进展,重新将华北克拉通中东部划分为2个一级重磁异常单元和7个二级重磁异常单元;重点描述了7条分划性断裂的重磁特征,特别指出中国东部重力梯度带正是华北克拉通中部带的集中表现,而郯庐断裂带和兰考～聊城～盐山～台安-大洼断裂带是燕山期陆内不同刚性块体调整的重要边界,所以也是重磁特征的变异带．据此,对华北克拉通断裂与构造单元的重磁异常特征赋予了新的地质意义．研究表明,华北克拉通现今的地球物理特征能够反映结晶基底构造,其原因是华北克拉通现今构造格局是中新生代构造继承结晶基底构造的结果． 相似文献
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Pierre Keating 《Geophysical Prospecting》1995,43(4):569-580
Gravity data are often acquired over long periods of time using different instruments and various survey techniques, resulting in data sets of non-uniform accuracy. As station locations are inhomogeneously distributed, gravity values are interpolated on to a regular grid to allow further processing, such as computing horizontal or vertical gradients. Some interpolation techniques can estimate the interpolation error. Although estimation of the error due to interpolation is of importance, it is more useful to estimate the maximum gravity anomaly that may have gone undetected by a survey. This is equivalent to the determination of the maximum mass whose gravity anomaly will be undetected at any station location, given the data accuracy at each station. Assuming that the maximum density contrast present in the survey area is known or can be reasonably assumed from a knowledge of the geology, the proposed procedure is as follows: at every grid node, the maximum mass whose gravity anomaly does not disturb any of the surrounding observed gravity values by more than their accuracies is determined. A finite vertical cylinder is used as the mass model in the computations. The resulting map gives the maximum detection error and, as such, it is a worst-case scenario. Moreover, the map can be used to optimize future gravity surveys: new stations should be located at, or near, map maxima. The technique is applied to a set of gravity observations obtained from different surveys made over a period of more than 40 years in the Abitibi Greenstone Belt in eastern Canada. 相似文献
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观测表明,大陆地区存在很多传统均衡模型无法解释的现象,其根本原因在于传统均衡理论中没有考虑地幔岩石圈部分由于热结构差异导致密度差异的影响.本文基于岩石圈尺度的质量平衡模型研究了中国大陆20个构造单元地壳及地幔岩石圈对地形海拔的贡献,以及各块体的均衡状态.计算结果表明,在一些地区,如塔里木盆地、北山和柴达木盆地,尽管岩石圈均衡模型和Airy模型得到了一致的海拔值,但岩石圈均衡模型更能体现均衡过程的物理本质;除青藏高原造山带外的多数块体,岩石圈均衡模型的计算结果更接近观测海拔和地表垂直运动状态;总体上,考虑地幔岩石圈热结构影响后,中国大陆各地区的均衡结果普遍优于传统的均衡模型.通过对均衡状态分析,我们得到以下主要结论：(1)构造稳定地区均衡程度较高;(2) 青藏高原及周边造山带现今地壳运动主要为区域构造过程及深部动力学过程所控制,均衡调整过程不是主要控制因素;(3) 现今地壳垂直运动比较明显的块体处于均衡调整阶段,地表垂直运动的大小反映了该区所受的均衡力作用的程度;(4) 构造稳定地区基于岩石层均衡的理论计算海拔与观测海拔之差值和现今地壳垂直运动速率有较好的相关性,据此我们可以通过均衡分析研究构造块体的运动趋势和动力学性质;(5) 地幔热结构对现今地形、海拔及地壳垂直运动有显著影响,在处理均衡问题时,地幔岩石圈热结构是我们必须考虑的重要因素. 相似文献
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由试验均衡的理论出发,得到了该区的均衡响应函数并建立了复合补偿模式。地形高度对重力场的影响很复杂,波长小于300km的地形起伏具有偏高的均衡响应值。 局部补偿是华北地区的主要补偿机制,所占比例达90%。区域补偿的等效弹性板厚度偏小,仅18km, 表明了华北地壳破裂程度严重和下地壳流变性突出。 均衡重力异常具有块体分布和均衡调整方向同新生代构造运动方向不完全符合等特点,其中一些成分是由于表浅层地质体的非均匀载荷所造成,不能简单地归因于欠补偿或过补偿。均衡异常的垂直导数分布清晰地揭示了华北地区几条重要的断块分界线。从深部构造上看,均衡补偿过程发生在下地壳特别是上地幔中。本文从均衡的角度探讨了地震危险性。 相似文献
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重力均衡与天山的构造运动 总被引：2，自引：0，他引：2
通过分析重力异常的特征，并结合地壳上地幔的物质结构，研究了天山地区的重力作用和结构力源，探讨了重力均衡补偿与现代构造运动的联系，对未来构造活动的趋势做出判断。一些迹象表明，除了板块之间的水平作用力以外，地幔热物质的上涌也是影响天山地区构造活动的原因之一。 相似文献
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Combining T/P altimetric data with hydrographic data to estimate the mean dynamic topography of the North Atlantic and improve the geoid 总被引：1，自引：0，他引：1
The mean dynamic topography of the surface of the North Atlantic is estimated using an inverse model of the ocean circulation constrained by hydro-graphic and altimetric observations. In the North Atlantic, altimetric observations have no significant impact on the topography estimate because of the limited precision of available geoid height models. They have a significant impact, however, when uncertainties in the density field are increased to simulate interpolation errors in regions where hydrographic data are scarce. This result, which moderates the conclusion drawn by Ganachaud and co-workers of no significant contribution of altimetric observations to the determination of the large-scale steady circulation, reflects the simple idea that altimetric data are most useful near the surface of the ocean and in areas where the hydrography is poorly determined. One application of the present inverse estimate of the mean dynamic topography is to compute a geoid height correction over the North Atlantic which reduces the uncertainty in the geoid height expanded to spherical harmonic 40 down to a level of about 5 cm. 相似文献
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Christian Hirt Sten J. Claessens Michael Kuhn Will E. Featherstone 《Studia Geophysica et Geodaetica》2012,56(4):957-975
Curtin University??s Mars Gravity Model 2011 (MGM2011) is a high-resolution composite set of gravity field functionals that uses topography-implied gravity effects at medium- and short-scales (??125 km to ??3 km) to augment the space-collected MRO110B2 gravity model. Ground-truth gravity observations that could be used for direct validation of MGM2011 are not available on Mars??s surface. To indirectly evaluate MGM2011 and its modelling principles, an as-close-as-possible replication of the MGM2011 modelling approach was performed on Earth as the planetary body with most detailed gravity field knowledge available. Comparisons among six ground-truth data sets (gravity disturbances, quasigeoid undulations and vertical deflections) and the MGM2011-replication over Europe and North America show unanimously that topography-implied gravity information improves upon space-collected gravity models over areas with rugged terrain. The improvements are ??55% and ??67% for gravity disturbances, ??12% and ??47% for quasigeoid undulations, and ??30% to ??50% for vertical deflections. Given that the correlation between space-collected gravity and topography is higher for Mars than Earth at spatial scales of a few 100 km, topography-implied gravity effects are more dominant on Mars. It is therefore reasonable to infer that the MGM2011 modelling approach is suitable, offering an improvement over space-collected Martian gravity field models. 相似文献
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大同地区几次中强震前后的重力变化 总被引：5，自引：0，他引：5
本文对华北北环重力重复测量资料进行了分析研究，探讨了排除浅层干扰因素，提取与地震相关的重力变化的途径。以大同地震为例，详细分析了地震前后重力场变化，结果表明，其变化是明显的，远远超过了各项误差。 相似文献
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Modified image algorithm to simulate seismic channel waves in 3D tunnel model with rugged free surfaces 总被引：1，自引：0，他引：1 
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下载免费PDF全文 The existence of rugged free‐surface three‐dimensional tunnel conditions in the coal seams, caused either by geological or mining processes, will inevitably influence wave propagation characteristics when the seismic waves go through the coal mines. Thus, a modified image algorithm has been developed to account for seismic channel waves propagating through this complicated topography with irregular free surfaces. Moreover, the seismic channel waves commonly exhibit damped and dispersive signatures, which is not only because of their own unique sandwich geometry of rock–coal–rock but also because of the viscoelastic behavior of coal. Considering the complexity of programming in three‐dimensional tunnel models with rugged free surfaces, an optimized vacuum grid search algorithm, enabling to model highly irregular topography and to compute efficiently, is also proposed when using high‐order staggered finite‐difference scheme to simulate seismic channel wave propagations in viscoelastic media. The numerical simulations are implemented to investigate the accuracy and stability of the method and the impact of coal's viscoelastic behavior on seismic channel wave propagation characteristics. The results indicate that the automatic vacuum grid search algorithm can be easily merged into high‐order staggered finite‐difference scheme, which can efficiently be applied to calculate three‐dimensional tunnel models with rugged free surfaces in the viscoelastic media. The simulation also suggests that the occurrence of a three‐dimensional tunnel with free surfaces has a remarkable influence on the seismic channel wave propagation characteristics and elastic energy distribution. 相似文献
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《Earth and Planetary Science Letters》2003,205(3-4):195-210
Lake Vostok, located beneath more than 4 km of ice in the middle of East Antarctica, is a unique subglacial habitat and may contain microorganisms with distinct adaptations to such an extreme environment. Melting and freezing at the base of the ice sheet, which slowly flows across the lake, controls the flux of water, biota and sediment particles through the lake. The influx of thermal energy, however, is limited to contributions from below. Thus the geological origin of Lake Vostok is a critical boundary condition for the subglacial ecosystem. We present the first comprehensive maps of ice surface, ice thickness and subglacial topography around Lake Vostok. The ice flow across the lake and the landscape setting are closely linked to the geological origin of Lake Vostok. Our data show that Lake Vostok is located along a major geological boundary. Magnetic and gravity data are distinct east and west of the lake, as is the roughness of the subglacial topography. The physiographic setting of the lake has important consequences for the ice flow and thus the melting and freezing pattern and the lake’s circulation. Lake Vostok is a tectonically controlled subglacial lake. The tectonic processes provided the space for a unique habitat and recent minor tectonic activity could have the potential to introduce small, but significant amounts of thermal energy into the lake. 相似文献