多类资料计算南海重力垂直梯度的方法比较

重力垂直梯度在解决和解释地球表层地质和地球物理问题中的作用日益明显,因而获得其模型和分布是非常必要的。利用测高卫星可以得到空间大范围高精度、高分辨率的垂线偏差、重力异常以及大地水准面数据,利用测高重力资料和地球重力场模型,采用不同方法分别计算了南海海域重力垂直梯度,并对它们进行了比较。     

Geophysical implications of Izu–Bonin mantle wedge hydration from chemical geodynamic modeling

Using two-dimensional dynamic models of the Northern Izu–Bonin (NIB) subduction zone, we show that a particular localized low-viscosity (η_LV =  3.3 × 10¹⁹ − 4.0 × 10²⁰ Pa s), low-density (Δρ ∼ −10 kg/m³ relative to ambient mantle) geometry within the wedge is required to match surface observations of topography, gravity, and geoid anomalies. The hydration structure resulting in this low-viscosity, low-density geometry develops due to fluid release into the wedge within a depth interval from 150 to 350 km and is consistent with results from coupled geochemical and geodynamic modeling of the NIB subduction system and from previous uncoupled models of the wedge beneath the Japan arcs. The source of the fluids can be either subducting lithospheric serpentinite or stable hydrous phases in the wedge such as serpentine or chlorite. On the basis of this modeling, predictions can be made as to the specific low-viscosity geometries associated with geophysical surface observables for other subduction zones based on regional subduction parameters such as subducting slab age.     

确定全球厘米级精度大地水准面的可能性和方法探讨

阐述确定厘米级精度大地水准面所面临的挑战,评述各种大地水准面的定义,提出一种确定1°×1°厘米级精度全球大地水准面的新思路和新方法:在已知相应厘米级精度全球重力位模型、地形密度分布模型以及平均海面高模型的前提下,利用虚拟压缩恢复法可实现全球1°×1°厘米级精度大地水准面的目标。初步论证实现此目标的可能性和条件,并简要介绍一个模拟实验结果。     

球面小波分析技术及在全球重力模型中的应用

在介绍球面小波理论的基础上,推导和比较了几种球面小波,分析了最新地球重力模型——EGM96,以此为依据,把球面小波多分辨分析用于计算全球自由空气异常及重力大地水准面,并对处理结果做出解释。     

Coseismic and post-seismic signatures of the Sumatra 2004 December and 2005 March earthquakes in GRACE satellite gravity

The GRACE satellite mission has been measuring the Earth's gravity field and its temporal variations since 2002 April. Although these variations are mainly due to mass transfer within the geofluid envelops, they also result from mass displacements associated with phenomena including glacial isostatic adjustment and earthquakes. However, these last contributions are difficult to isolate because of the presence of noise and of geofluid signals, and because of GRACE's coarse spatial resolution (>400 km half-wavelength). In this paper, we show that a wavelet analysis on the sphere helps to retrieve earthquake signatures from GRACE geoid products. Using a wavelet analysis of GRACE geoids products, we show that the geoid variations caused by the 2004 December ( M _w= 9.2) and 2005 March ( M _w= 8.7) Sumatra earthquakes can be detected. At GRACE resolution, the 2004 December earthquake produced a strong coseismic decrease of the gravity field in the Andaman Sea, followed by relaxation in the area affected by both the Andaman 2004 and the Nias 2005 earthquakes. We find two characteristic timescales for the relaxation, with a fast variation occurring in the vicinity of the Central Andaman ridge. We discuss our coseismic observations in terms of density changes of crustal and upper-mantle rocks, and of the vertical displacements in the Andaman Sea. We interpret the post-seismic signal in terms of the viscoelastic response of the Earth's mantle. The transient component of the relaxation may indicate the presence of hot, viscous material beneath the active Central Andaman Basin.     

23届IUGG大会有关大地测量的最新进展

第23届国际大地测量与地球物理联合会综合性学术大会于2003年6月30日至7月11日在日本扎幌举行.介绍了这次大会中有关大地测量的最新发展.主要内容有国家和地区地心参考框架的建设与维护、地球重力场与大地水准面的精密测定、GPS及其应用、大地测量的基本理论与方法、地球动力学研究以及国际大地测量学会通过的新决议.     

珠峰高程测定中的有关问题及思考

对珠峰高程的精度、雪层的厚度、高程基准--大地水准面的精度、地壳的垂直运动以及如何将似大地水准面转换到大地水准面进行了讨论。结果显示,采用正常高加转换公式中的重力或地形资料求取珠峰正高比较合适。     

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