重力异常频谱分析方法研究与应用

Gravity Anomaly Spectrum Analysis Method and Its Application

频谱分析是以波数为自变量对位场异常频谱进行分析研究,从而解决实际工作中的异常转换、滤波、正反演等问题。位场的频谱特征包含了地下地层的空间分布、岩性及构造特征,有助于地球物理资料的解释、分析,为进一步了解研究区域概况提供信息。位场异常谱中的振幅谱与地下地质体的埋深、宽度与物性都有直接的关系;相位谱则反映了地下地质体的水平位置与倾角信息。计算了多种类型模型的频谱曲线,分析频谱曲线特征,并详细说明了模型参数变化对频谱曲线的影响;阐述了振幅谱反演、相位谱反演方法,提出了频率域联合反演方法,精确地反演模型的几何参数。将此方法应用于武清凹陷地层分析,反演得到了两个观测剖面的目标层深度和宽度,与实测地震资料对比,表现出较好的反演结果。

Objectives:Spectral analysis is to analyze and study various spectra of potential anomalies with wave-number as the independent variable,to solve the problems of anomaly conversion,filtering and forward and inverse analysis in practical work.The spectral characteristics of the potential,which include the spatial distribution,lithology and tectonic characteristics of the subsurface stratum,help the interpretation and analysis of geophysical data and provide information for further understanding of the study area.The amplitude spectrum of the potential anomaly spectrum is directly related to the burial depth,width of the subsurface geological body;the phase spectrum reflects the information of the horizontal position and dip angle of the subsurface geological body.However,in previous studies,most of the researchers’work had been focused on making use of the characteristics of fast calculation of the bitfield data in the frequency domain,doing a lot of forward work as well as applying the relationship between the spectrum and the parameters of the geologic body for inversion,but the analysis of the spectral characteristics of different geologic bodies and the specific effects of the geologic body parameters on the spectrum have been less studied.On the other hand,there are few studies on the joint inversion using different spectra in the frequency domain inversion.Methods:In order to better carry out the study of gravity anomaly in the frequency domain,using the characteristics of simple,solvable and easy to program and fast computation of the expression for the positive inversion of gravity anomaly in the frequency domain,the spectral curves of various models are calculated,and the characteristics of the spectral curves,and detailed effects of model parameter changes on the spectral curves are analyzed too.It also includes how to interpret the amplitude spectral inversion and phase spectral inversion,and proposes a joint inversion method in the frequency domain to accurately invert the geometric parameters of the models.Results:The gravitational anomaly spectrum of a horizontal cylinder,which is of the periodic fluctuation type with monotonically decreasing amplitude spectrum and its phase spectrum is a straight line with a negative slope;the gravity anomaly spectrum of the tilted thin plate is periodically fluctuating,with monotonically decreasing amplitude spectrum and fluctuating phase spectrum;the gravity anomaly spectrum of the tilted thick plate is periodically fluctuating with fluctuating amplitude spectrum and fluctuating and progressive phase spectrum.By analyzing the influence of different parameter changes of the thick plate on the model spectrum,the trend of the subsurface geological body is judged according to the spectrum changes.The amplitude spectrum can determine the burial depth of the model,and the change of its first zero value point position is determined in the horizontal direction of the model,and the phase spectrum is directly related to the model parameters.Conclusions:The joint inversion in frequency domain is an effective method to combine the advantages of amplitude spectrum inversion and phase spectrum inversion to accurately calculate the geometric parameters of the model.The method was applied to the inversion of the target stratigraphy in the Wuqing Sag,and the precise depth and width of the target substratum in the two measured sections were obtained,providing a basis for further seismic studies in the area.