基于GPS非差观测值进行精密单点定位研究

介绍了精密单点定位所用的数学模型及解算方案，着重分析了基于GPS非差双频观测值进行精密单点定位的误差模型、数据质量控制方法、卫星钟差的估算和内插、数据和解的一致性及精密单点定位能达到的精度等问题，并和双差结果作了比较。结果表明，利用精密星历及卫星钟改正参数的精密单点定位可达到cm级精度。     

Sedimentary Basins in the Western White Nile, Sudan, as Indicated by a Gravity Survey

An academic geophysical research as a regional gravity survey was made during 1994 in the Western White Nile to infer the shallow crustal structures in the area. The result of the survey was compiled as a Bouguer anomaly map with a contour interval of 2 ×10-5m/s2. It is found that the negative residual anomalies are related to the Upper Cretaceous sediments (Nubian Sandstone Formation) filling all depressions in the Basement complex surface while the positive residual anomalies are attributed to the relatively shallow or outcropping Basement rocks and the steep gravity gradients are resulting from the sharp contacts between the sedimentary infill and the Basement rocks. To define the geological structures in the area, 9 profiles were studied. For each of the profiles, measured and computed Bouguer gravity anomalies, crustal density model, subsurface geology evaluation were performed. A G-model computer program was applied in the gravity modeling, which is based on the line-integral method of gravity computation. A geological/structural map was proposed showing inferred sedimentary basins, faulting troughs and uplifted Basement block and tectonic trends. The basins are believed to be fault-controlled which developed by extensional tectonics (pull-apart mechanism). As for the mechanism and cause of faulting, the area is considered as a part of the Central Sudan rift system which had been subjected to several tectonic events since Early Cambrian to Tertiary times which resulted in the formation of several fracture systems associated with block subsidence, rifting and basin formation.     

布格重力异常建模反演在二连盆地油气勘探中的应用

二连盆地由众多小凹陷组成,伊和凹陷是其中之一.重力资料在盆地"探边摸底"、"定凹选带"等方面发挥着重要作用.本文基于布格重力异常资料,利用2.5D建模反演技术对其中横跨主洼槽的两条测线进行可视化建模及正演拟合.其中,初始模型的几何参数取自二维地震解释结果;物性参数中的纵向密度取自测井声波波速与密度的相关公式.正演拟合为建模反演技术的关键环节,密度横向变化,是在拟合过程中通过人机交互试错调整实现.通过正演拟合,揭示了主洼槽沉积层横向和纵向均存在较大的密度不均匀性,主洼槽有利于油气生成.与地震解释结果对比,二者在赛汉组-第四纪、腾格尔组深度相差不大,但凹陷底部拟合结果与地震解释结果有明显差异.通过钻井结果验证,正演拟合各沉积层深度与钻井揭示的各层深度结果一致,二维地震解释结果偏浅,其可能原因是时深转换选取的速度值偏小造成.     

重力与地形数据揭示的巴颜喀拉块体东缘垂向构造应力场

利用基于消去-恢复原理的最小二乘配置方法,对2009-2013年相对重力/GPS联合观测数据与EGM2008模型数据进行融合,更新了巴颜喀拉块体东缘地区的自由空气与布格重力异常场.基于该布格重力异常数据,以CRUST1.0地壳密度模型为初始条件,使用二维多边形棱柱体正演与非线性最小二乘反演方法,获取了巴颜喀拉块体东缘地壳分层密度结构.基于地壳不可压缩和均衡调整原理提出了计算垂向构造应力新方法,并结合上述地壳分层密度结构和地形数据计算了巴颜喀拉块体东缘垂向构造应力分布.结果表明,龙门山断裂带中南段蓄积了较高的正向构造应力(约40 MPa),马尔康周边地区蓄积了较高的负向构造应力(约—30 MPa).对研究区域1970年以来5级(Ms)以上地震进行统计发现,地震多发生在垂向构造应力梯度带上,垂向构造应力为正的地区易触发浅源地震,为负的地区易触发深源地震.在地壳横向变形强烈的区域,垂向构造应力与地震深度的对应关系减弱.     

羌塘地块中部南北向断裂的构造特征及其动力学意义

青藏高原内部除大规模的东西向走滑断裂以外,另一个显著的地质特征就是在藏南及高原腹地广泛发育东西向的伸展构造,形成走向近南北的断裂构造,如亚东一谷露裂谷带及双湖断裂.伸展构造已经成为青藏高原地质研究的一个焦点问题.在羌塘地块89°E附近存在明显的低重力、负磁、深度达300 km的低速异常及连通壳幔的高导异常,且地表伴生大规模的新生代火山岩,这些特殊的地质及地球物理场特征的发生位置与地表双湖断裂的位置基本对应.本文通过卫星重力数据的多尺度小波分析结果发现,双湖断裂之下,存在一明显由上地壳一直向下延伸至地幔深部的低重力异常,说明双湖断裂向下延伸深度大,且上下连通性好.结合已有的地质和地球物理资料,认为由于双湖断裂的存在,使得深部幔源岩浆沿断裂构造薄弱带上涌,从而导致羌塘地块之下壳幔温度的升高及大规模部分熔融的发生.     

SSR改正数更新频率及中断时间间隔对实时PPP的影响分析

实验模拟服务器端不同更新频率的SSR改正数对实时精密单点定位的影响,以及客户端改正数中断时长对实时精密单点定位的影响。结果表明,服务器端SSR改正数的播发频率控制在30 s以内可获得cm级定位精度;客户端的SSR改正数中断在150 s之内可获得cm级定位精度,改正数中断200 s可获得20 cm的定位精度,改正数中断300 s可获得亚m级定位精度。     

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Integrated 3D density modelling and segmentation of the Dead Sea Transform

A 3D interpretation of the newly compiled Bouguer anomaly in the area of the “Dead Sea Rift” is presented. A high-resolution 3D model constrained with the seismic results reveals the crustal thickness and density distribution beneath the Arava/Araba Valley (AV), the region between the Dead Sea and the Gulf of Aqaba/Elat. The Bouguer anomalies along the axial portion of the AV, as deduced from the modelling results, are mainly caused by deep-seated sedimentary basins (D > 10 km). An inferred zone of intrusion coincides with the maximum gravity anomaly on the eastern flank of the AV. The intrusion is displaced at different sectors along the NNW–SSE direction. The zone of maximum crustal thinning (depth 30 km) is attained in the western sector at the Mediterranean. The southeastern plateau, on the other hand, shows by far the largest crustal thickness of the region (38–42 km). Linked to the left lateral movement of approx. 105 km at the boundary between the African and Arabian plate, and constrained with recent seismic data, a small asymmetric topography of the Moho beneath the Dead Sea Transform (DST) was modelled. The thickness and density of the crust suggest that the AV is underlain by continental crust. The deep basins, the relatively large intrusion and the asymmetric topography of the Moho lead to the conclusion that a small-scale asthenospheric upwelling could be responsible for the thinning of the crust and subsequent creation of the Dead Sea basin during the left lateral movement. A clear segmentation along the strike of the DST was obtained by curvature analysis: the northern part in the neighbourhood of the Dead Sea is characterised by high curvature of the residual gravity field. Flexural rigidity calculations result in very low values of effective elastic lithospheric thickness (t _e < 5 km). This points to decoupling of crust in the Dead Sea area. In the central, AV the curvature is less pronounced and t _e increases to approximately 10 km. Curvature is high again in the southernmost part near the Aqaba region. Solutions of Euler deconvolution were visualised together with modelled density bodies and fit very well into the density model structures. An erratum to this article can be found at     

Variation of crustal thickness in the Philippine Sea deduced from three-dimensional gravity modeling

Abstract   Crustal thickness of the northern to central Philippine Sea was gravimetrically determined on the simple assumption of four layers: seawater, sediments, crust and lithospheric mantle, with densities of 1030, 2300, 2800 and 3300 kg/m³, respectively. As for the correction of the regional gravity variation, a 15 km difference of the lithospheric thickness with a density difference of 50 kg/m³ against the asthenosphere below between both sides of the Kyushu-Palau Ridge was taken into consideration. Mantle Bouguer anomalies were calculated on the assumption of constant crustal thickness of 6 km, and then the crustal thickness was obtained by three-dimensional gravity inversion method. The results show occurrence of thin crust areas with a thickness of approximately 5 km in the southern part and at the western margin of the Shikoku Basin and also of thick crust areas in the northwestern and northeastern parts of the Parece Vela Basin. We suggest that these are because of the variation of magma supply at the time of sea floor spreading in the Shikoku and Parece Vela Basins, which is possibly related to the variation of spreading rate and enhanced magmatism near the past arc volcanic fronts. The results further show the occurrence of crust thinner than 5 km in the northeastern part of the West Philippine Basin, of crust thicker than 15 km in the Amami Plateau, the Daito and Oki-Daito Ridges, and also in the northern part of Kyushu-Palau Ridge, whereas the southern part of the Kyushu-Palau Ridge the crust is thicker than 10 km. It was also inferred that small basins in the Daito Ridge province have the thinnest oceanic crust of less than 5 km in the Kita-Daito Basin.     

The gravitational attraction of any polygonally shaped vertical prism with inclined top and bottom faces

 A closed formula for computing the gravitational attraction of a general vertical prism with N+2 faces (N faces are vertical planes, the other two are the inclined top and bottom planes) in Cartesian coordinates is presented. In addition, the special case of a triangular prism is discussed. Algebraic differences and overlooked singularity conditions of a previously published formula of this computation (which was only for the triangular special case) were identified and are also presented. Received: 22 March 1999 / Accepted: 2 February 2000