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201.
202.
Gary J. Barnes John M. Lumley Phill I. Houghton Richard J. Gleave 《Geophysical Prospecting》2011,59(1):176-187
Noise levels in marine and airborne full tensor gravity gradiometer surveys together with conventional land, marine and airborne gravity surveys are estimated and analysed in gridded form, resulting in relations that detail how these different survey systems can be compared analytically. After defining survey parameters including line spacing, speed and instrument bandwidth, the relations estimate the noise levels that result on either grids of gravity (gz) or gravity gradient (Gzz) as a function of the spatial filtering often applied during geological interpretation. Such comparisons are believed to be a useful preliminary guide for survey selection and planning. 相似文献
203.
D. Franke U. BarckhausenN. Baristeas M. EngelsS. Ladage R. LutzJ. Montano N. PellejeraE.G. Ramos M. Schnabel 《Marine and Petroleum Geology》2011,28(6):1187-1204
The South China Sea formed by magma-poor, or intermediate volcanic rifting in the Paleogene. We investigate the structure of the continent-ocean transition (COT) at its southern margin, off NW Palawan between the continental blocks of Reed Bank and the islands of Palawan and Calamian. Several surveys, recorded by the BGR from 1979 to 2008, established a comprehensive database of regional seismic lines, accompanied with magnetic and gravity profiles.We interpret two major rifted basins, extending in the NE direction across the shelf and slope, separated by a structural high of non volcanic origin.The continent-ocean transition is interpreted at the seaward limit of the continental crust, when magnetic spreading anomalies terminate some 80-100 km farther north. The area in between displays extensive volcanism - as manifest by extrusions that occasionally reach and cut the seafloor, by dykes, and by presumed basaltic lava flows - occurring after break-up.The COT is highly variable along the NW Palawan slope: One type shows a distinct outer ridge at the COT with a steep modern seafloor relief. The other type is characterised by rotated fault blocks, bounded by listric normal faults ramping down to a common detachment surface. Half-grabens developed above a strongly eroded pre-rift basement. The seafloor relief is smooth across this other type of COT.We suggest the pre-rift lithospheric configuration had major influence on the formation of the COT, besides transfer zones. Volcanic domains, confined to the north of competent crustal blocks correlate with the style of the COT.Gravity modelling revealed an extremely thinned crust across the shelf. We propose a depth-dependent extension model with crust being decoupled from mantle lithosphere, explaining the discrepancy of subsidence observed across the South China Sea region. 相似文献
204.
205.
2002年6月17日海城4.0级地震前后重力场变化特征探讨 总被引:1,自引:0,他引:1
分析了2002年6月17日海城4.0级地震前后海城一带重力场时空变化情况,重力点值和段差值变化在时间和幅度上具有明显的同步性,分析认为此次地震的发生与重力场变化有着密切关系。 相似文献
206.
基于卫星轨道运动的能量积分方程,可导出利用卫星跟踪卫星数据求解地球重力场的实用公式.本文在Jekeli给出的公式基础上导出了基于能量守恒方程利用两颗低-低卫星跟踪的扰动位差求解重力位系数的严密关系式.基于两颗GRACE卫星的观测数据,采用本文导出的严密能量积分方法求解得到120阶的GRACE地球重力场模型,命名为WHU-GM-05;将WHU-GM-05模型与国际上同类重力场模型EIGEN-GRACE系列和GGM02S分别在阶方差和大地水准面高等方面作了比较,并与美国和中国的部分地区GPS水准观测值进行了精度分析.结果表明基于本文推导的严密双星能量守恒方程得到的WHU-GM-05重力场模型精度与国际上同类重力场模型的精度相当. 相似文献
207.
Lech Krysiński 《Pure and Applied Geophysics》2009,166(3):375-408
The paper describes a new method of gravity modelling of the density cross section along a DSS profile. We propose a systematic
procedure of gravity interpretation using structural information contained both in the velocity distribution of the seismic
model and the geometry of its layers. The procedure is based on the optimisation of the density parameters of the model. The
values of the parameters are limited by relationships between the seismic velocity and the density (optimisation with inequalities).
The formulation of the method allows for discussion of the presence of isostasy and the distribution of compensating masses.
The discussion is very important for the considered crust-lithosphere system. The presented calculations are done for one
Carpathian profile (CEL01). The analysis of the properties of the fitting procedure provides the characteristic depth of subcrustal
compensating density structures, the position of crucial tectonic boundaries along the profiles, locations of the crustal
areas having exceptional lithology, the regional density differences of subcrustal matter and the estimation of regional deviations
from the isostatic equilibrium. 相似文献
208.
汶川MS8.0地震的“孕育”、发生和发展是深部物质分异、调整和运移的产物.为此,在四川中西部地区(松潘—甘孜,龙门山断裂系和四川盆地)应用重力布格异常场资料并通过两条典型剖面的地壳厚度(Moho界面深度)分布与依据Airy均衡理论给出的理论均衡地壳厚度做对比分析,探讨四川盆地、龙门山造山带、邛崃山等川西地域的地壳均衡状态,得到龙门山及其以西地带的深部地壳结构.龙门山造山带恰处于很不均衡的状态,即与其西北和东南部相比差异明显,故地壳处于不稳定状态.为探讨该区重力场均衡与强烈地震活动之间的关系,还必须进行新一轮的高精度观测,以对该区深部精细结构、重力场效应和均衡补偿深入研究.此外,本文研究结果有益于震后确定城镇布局和为不同类型建筑物重建选址提供深部要素. 相似文献
209.
To improve our knowledge of the structural pattern of Mt. Vesuvius and its magmatic system, which represents one of the three
volcanoes located in the Neapolitan area (together with Campi Flegrei and Ischia; southern Italy), we analyze here the Bouguer
gravity map that is already available through its interpretation by means of 2.5-dimensional modelling. We have carried out
a three-dimensional interpretation using a new and original algorithm, known as ‘Layers’, that has been especially processed
for this purpose. Layers works in an automatic and non-subjective way, and allows the definition of the structural settings
in terms of several layers, each representing a specific geological formation. The same data are also interpreted in terms
of isolated and shallow anomalous density bodies using a well tested algorithm known as ‘Growth’. We focus our inversions
on the Mt. Vesuvius volcano, while globally analyzing the entire Neapolitan area, in order to investigate the deep structures,
and in particular the deep extended ‘sill’ that has been revealed by seismic tomography.
The final models generally confirm the global setting of the area as outlined by previous investigations, mainly for the shape
and depth of the carbonate basement below Mt. Vesuvius. The presence of lateral density contrasts inside the volcano edifice
is also shown, which was only hypothesized in the 2.5-dimensional inversion. Moreover, the models allow us to note a high
density body that rises from the top of the carbonate basement and further elongates above sea level. This probably represents
an uprising of the same basement, which is just below the volcano and which coincides with the VP and VP/VS anomalies detected under the crater. The three-dimensional results also reveal that the two inversion methods provide very
similar models, where the high density isolated body in the Growth model can be associated with the rising high density anomaly
in the Layers model. Taking into account the density of these modelled bodies, we would also suggest that they represent solidified
magma bodies, as suggested by other studies. Finally, we did not clearly detect any deep anomalous body that can be associated
with the sill that was suggested by seismic tomography. 相似文献
210.
Vibrator excitation generates not only reflections and refractions of wave fields on the subsurface interfaces but also electromagnetic waves with different frequencies. In this paper, we address the vibration-induced effects on the spontaneous potential field. The effects of controllable vibration on the spontaneous potential field were studied under real field geologic conditions. Experimental data confirmed that the vibration-induced effects on the spontaneous potential field do exist under field conditions. Monitoring records over a long time interval showed that there exist three information zones in the vibration-induced effects on the spontaneous potential field. These are the signal-varying zone, the extremestable zone, and the relaxation-recovery zone. Combined with different well-site data, it was concluded that the time-varying features of the anomalies in the information zones was closely related to the properties of the subsurface liquid (oil and water). 相似文献