重磁场的变差函数特征及应用

Characteristics and Applications of Variogram for Gravity and Magnetic Fields

用变差函数研究重磁场的区域变化特征.变差函数的变程反映重磁场的相干范围,块金效应反映随机干扰,基台值反映变异程度.重磁场的理论模拟说明:重力场的相干范围大于磁场,重磁场变程主要取决于场源深度,浅源重磁场变差函数近似为球状模型或指数模型,深源重磁场近似为连续性更好的高斯模型.磁场场源深度近似等于变程的一半,重力场场源深度近似等于变程的四分之一.湖北大冶铁矿垂直分量磁异常具有几何各向异性,北西-南东走向,变差函数推测磁铁矿平均深度为250m.磁异常小波多尺度分解细节和逼近部分磁场具有协调几何各向异性,变差函数的各阶场源深度估计结果与功率谱估计结果吻合.

The variogram is used to investigate the regional variation characteristics of gravity and magnetic fields in this study.The range of variogram reflects the coherent area;the nugget effect represents the random disturbance;and the sill means the variation degree.The theoretical simulations involving gravity and magnetic fields show that the coherent range of gravity field is larger than that of magnetic field.The range of potential gravity and magnetic field is mainly determined by the depth of field sources.The variogram for shallow sources is approximate to be a spherical or exponential model,while with the increase of the depth,it nearly becomes a more continuously Gaussian model.The depth of magnetic source is approximately equal to the half of the range,whereas the depth of gravity source is approximately equal to one quarter of the range.The real example of the vertical component magnetic anomaly of the Daye iron-ore deposit in Hubei has geometric anisotropy striking northwestsoutheast direction.The variogram reveals that the average depth of magnetite orebodies is about 250 m.The decomposed details and approximations of magnetic anomaly using wavelet transform have the coordinate geometric anisotropy.And the estimated depths using variogram ranges are in agreement with those gained by power spectrum method.