Research On Fine Interpretation And Joint Inversion Of Comprehensive Geophysics In Active Fault Field

The frequent seismic activity in China,especially the complex hidden fault in the town of Beijing-Tianjin-Hebei region,restricts the construction and development of the city.In order to comprehensively and effectively grasp the distribution of active fault structures in different areas,the spatial characteristics and other information as well as to increase the accuracy and effectiveness of detection results,the integrated geophysical exploration method is often used.Besides,the data joint inversion and fine interpretation technology between different geophysical parameters become the key and difficult points.Joint inversion has evolved from the inversion of the original physical parameters and different exploration methods to the multidimensional joint inversion of various geophysical parameters.In particular,the joint inversion of structural coupling of various physical parameters is becoming the trend.According to the geological and comprehensive geophysical data obtained from the exploration of active faults in Beijing-Tianjin-Hebei region,the thesis analyzes the corresponding characteristics of seismic and electromagnetic fields caused by active faults through forward modeling,and represents a comprehensive interpretation of concealed active faults through adopting independent inversion and Cross gradient joint inversion method,which is based on the natural seismic observation data of seismic stations,field artificial seismic exploration data,CSAMT data,geological drilling and field investigation data.At the same time,in view of the difficulties and problems of different kinds of geophysical data processing,the fine data processing combination technology is adopted to explore the comprehensive data fine processing and the interpretation technology which is suitable for similar geological conditions.Through the comprehensive analysis of domestic and foreign classification standards and classification scheme of active faults,this thesis classifies the Beijing-Tianjin-Hebei region of active fault.The main active faults,spatial information and activity evaluation in the main fault active structural belt is analyzed and evaluated synthetically is based on the results of field geological surveyOn the basis of the propagation characteristics and principles of seismic wave field,the 2D and 3D high-order velocity stress equations and finite difference dispersion schemes with staggered grids are established for forward analysis,especially for the expression of fault activity,which is reflected by the characteristics of shallow layer cutting and fault zone caused by activity.Based on the propagation law and characteristics of electromagnetic field,the numerical analysis of primary field and staggered grid difference scheme of secondary field of CSAMT are established.Aiming at the forward calculation of cross gradient,this thesis focuses on the characteristic that the result of cross gradient algorithm is not obvious to the interface of abrupt mutation constant body.An improved joint algorithm of "negative slope" and cross gradient is proposed.The forward result of cross gradient algorithm has a better recognition of especially abrupt mutation interface.Combined with the improved velocity and interface inversion algorithm as well as the double difference seismic tomography algorithm,the inversion effect of natural seismic data is analyzed comprehensively.In view of the complex characteristics of active fault structure,the full waveform inversion method which is more sensitive to complex structure is selected with the cross gradient constraint to calculate the joint inversion algorithm of P-wave and S-wave.The constrained inversion method is used to realize the independent inversion of various geophysical data according to the known geology and borehole.For the structural similarity of active faults,the joint inversion method of seismic and CSAMT with cross gradient operator is realized.Especially when the active faults cut the interface of shallow weak physical parameters,the conjugate gradient algorithm is used to solve the joint inversion objective function,which improves the calculation efficiency and stability.In the inversion,multi grid strategy is adopted for grid generation,and cross gradient constraints are imposed on various geophysical parameters.In terms of the characteristics of many interference factors and low signal-to-noise ratio of seismic data collected in the field,the accurate spatial data is established and the refraction static correction,tomographic static correction,first arrival static correction and other comprehensive static correction methods as well as the accurate speed analysis,wavelet change,multiple iterative migration processing technology is applied to improve the seismic signal-to-noise ratio.In order to obtain the shallow,middle and deep geological information of active faults,the comprehensive exploration and joint interpretation methods are adopted,which are determined by borehole,high-density electrical method and shallow seismic exploration.In addition,the middle and deep structural information is mainly determined by the combination of seismic and CSAMT,combined with CSAMT interpretation,especially the natural seismic interpretation.The cross gradient joint inversion method is used to explain the secondary ground fractures caused by active faults,which shows the accuracy and effectiveness of the method.Based on the model of individual inversion,a variety of geophysical integrated data joint inversion technology uses the improved cross gradient structure constraint joint inversion algorithm,which has a significant effect on the precise interpretation of particularly steep active faults.