格莱尼改正及其在地球物理数据处理中的意义

格莱尼改正是重力改正的一种,是对球面半径约166.7 km以外地形和均衡造成的重力综合效应的改正,改正后所得格莱尼异常可对应研究区范围内地壳结构特征,具有重要的研究意义.但近年来国内的重力研究中,对格莱尼改正的认识和重要性还不是十分透彻,特别是在大区域研究中,忽略这一远区重力效应可能会对研究结果的解释造成误导.针对这一问题,本文介绍了格莱尼改正的含义、由来与研究历史,指出了在大区域研究中需要考虑格莱尼效应的重要性,以“扇形球壳块”法为例给出了格莱尼改正的计算原理,列举了格莱尼异常在地球物理中的常见应用,并通过重力改正与莫霍面深度反演实例,通过对反演结果的控制点检测与精度评价,指出格莱尼异常反演所得莫霍面埋深更接近地震方法结果,从而表明了格莱尼改正在地球物理研究中的不可忽视性,并指出完全布格改正与格莱尼改正在计算方法上可实现统一.

Glennie correction and its significance in data processing in geophysics

Glennie correction is one kind of gravity corrections used to eliminate the gravitational effect of the terrain and the corresponding isostatic compensation outside the region with the radius of about 166.7 km.The gravity anomalies calculated after imposing Glennie correction are called Glennie anomalies which directly correspond with the characteristics of the crustal structure in the range of the research area.It is thus meaningful in geophysical research.But recently,in domestic researches on gravity,researchers are not very much aware of the meaning and significance of applying Glennie correction especially in large-region researches where overlooking such correction may lead to misunderstandings in illustration of the research results.Thus,we need to reiterate the meaning and significance of Glennie correction.We introduced the meaning,origin and research history of Glennie correction and pointed out the significance of taking it into consideration in largeregion researches.The computational method was based on the model illustrating the surface of the globe as a series of fan-shaped spherical crustal blocks divided in accordance with the Hayford's scheme as recommended.We also introduced applications of Glennie correction and anomalies in obtaining the ages of oceanic lithosphere and depth distribution of Moho discontinuities.In the following case-study,we chose the research area in the South China Sea and calculated the corresponding complete Bouguer anomalies and Glennie anomalies.By means of regional field separation,we acquired the regional fields of complete Bouguer anomalies and Glennie anomalies,respectively.Then we calculated the depth distribution of Moho discontinuities based on the regional fields abovementioned and made comparison by calculating the differences as well as by introducing control points deriving from seismic results in essays that have been previously published.It indicates that the result of the depth distribution of Moho discontinuities based on the regional field of Glennie anomalies is closer to the seismic result in terms of both average differences and the Standard Deviation(STD),showing that Glennie anomalies better reflect the crustal structure in the research area.In large-region researches,Glennie anomalies perform better than Bouguer anomalies in inversion of the subterranean depth distribution.In the compilation of geology and geophysical maps,we recommend introducing the Glennie anomaly map.We also suggest that in the upcoming edition of Specification for Regional Gravity Survey,clarification of calculation method of Glennie anomalies is supposed to be given,and that complete Bouguer correction and Glennie correction may be algorithmically unified.