Multi-scale Gravity Inversion Of The Crustal Structure In Wuhan

Wuhan is the core city of the Yangtze River Economic Belt,located in the east of the Jianghan Plain.There are hidden faults in Wuhan,such as Tuanma fault and Xiangguang fault.When the hidden fault below the city suddenly and rapidly moves,it will trigger a destructive earthquake,causing large casualties and economic losses.Therefore,the study of the crustal structure in Wuhan is conducive to the planning and construction of Wuhan.Wuhan has carried out geological,geophysical and drilling investigations.These work provide the possibility of detailed exploration of hidden faults in Wuhan and analysis of the properties of Wuhan's crustal structure.However,these data only reveal shallow information and lack of deep urban signals,which is not conducive to the analysis of the crustal structure of Wuhan.The internal structure of the earth can be revealed by gravity data,which can effectively obtain urban crustal structure information.In this paper,high-precision and high-resolution gravity data is used to invert the crustal structure of Wuhan City,showing its crustal density distribution,fault distribution form,and Moho surface structure.Provide scientific basis for the construction of municipal projects.The multi-scale gravity inversion in this paper is as follows: fault identification method based on wavelet multi-scale separation,Parker-Olderburg iterative inversion method of Moho surface,layered horizontal tectonic stress inversion method for detecting fault distribution,and applying it to study Wuhan The city 's crustal structure provides comprehensive information about the distribution of crustal density,the distribution of hidden faults,and the structure of the Moho.The main work and results of this article are as follows:(1)Read relevant references to introduce the current research status of the Moho surface and crustal structure in the gravity inversion area.(2)Introduction of forward and inversion of gravity anomalies,study wavelet multi-scale analysis theory.(3)Using wavelet multi-scale separation of gravity anomalies to identify faults,and used to study hidden faults in Wuhan City,the main results include: 1)The depth of the Xinhuang fault range is 0-30 km,while the Tianmenhe fault,Yangtze River fault,Mayangtan The depth range of faults,Tuanma fault,Xiangguang fault and Yueyang-Wuhan fault are all 0-20km;and the distribution of faults gradually changes as the depth increases;2)Wuhan main deep faults are mainly divided into NNE andNWW two groups.NNE-trending faults include Tuanfeng-Macheng fault and Yangtze fault;NWW-trending faults include Xiangfan-Guangji fault,Xincheng-Huangpi fault,Tianmenhe fault and Mayangtan(Wulongquan)fault;3)The research results are similar to those of predecessors Better consistency.(4)Based on the wavelet multi-scale decomposition and extracted the gravity signal originating from the fluctuation of the Moho surface,the Parker-Olderburg iterative method is used to invert the Moho surface in Wuhan.The main results are as follows:1)The depth of the overall Moho surface in Wuhan is relatively small,ranging from29 km to 30.6km,and the depth difference is within 2km;2)In terms of spatial form,the undulation and topographic changes of the Moho surface in Wuhan There is a certain correlation.The Moho surface is the shallowest in the central plain area.The Moho surface gradually deepens after entering the northern and southern mountains,that is,it shows the characteristics of gradually deepening from the center to the northeast and southwest;3)According to structural geological data Carding,Wuhan resides in the junction of the Yangtze Land Block and the Qinling-Dabie Mountain Belt,and the main part belongs to the southeast Hubei fold and thrust belt of the Lower Yangtze Land Block in the Yangtze Land Block.The deepening trend of the Moho surface in the northeast may be affected by the Qinling-Dabie orogenic belt,while the deepening trend of the Moho surface in the southwest should be caused by tectonic compression.4)The research results are in good agreement with the predecessors.Therefore,the use of high-precision Bouguer gravity data for multi-scale gravity inversion of Wuhan Moho is feasible.(5)Based on the wavelet multi-scale separation results of the Bouguer gravity anomaly in Wuhan,the underground medium in Wuhan is reasonably stratified,and the gravity density anomaly density inversion method is used to calculate the underground stratified density in Wuhan,combined with the related prior data The main research results are as follows: 1)The density distribution characteristics of each layer have a good correspondence with the corresponding wavelet details;2)Wuhan City has a density structure in the upper crust of 1.4-8km and the middle and lower crust of 13-30 km Certain differences.The density structure in the upper crust is distributed in a strip shape,while the middle and lower crust becomes a block distribution;The direction of the long axis of the Moho plane is almost consistent,and it is consistent with the results of Wuhan City where the crustal stress is mainly northwest and northeast.Therefore,the inversion results of Wuhan City's crustalstratification density verify the correctness and effectiveness of the method,and also show the feasibility of inversion of Wuhan City's crustal stratification density structure using high-precision Bouguer gravity data.(6)Based on the calculation results of the underground layering density of Wuhan City,combined with the crustal tectonic stress inversion theory,calculate the horizontal structural stress of Wuhan City's underground layering.Using this method to study the hidden faults in Wuhan,the main results are as follows: 1)The stress distribution of each layer has a certain correlation with the fracture distribution and fracture properties.2)The overall horizontal structural stress of each layer is relatively small,and the overall range is 5.710-6Mpa-3.5Mpa,which is basically in a plane isobaric state,indicating that the fracture is basically stable.3)Although the stress on both sides of the fault changes,it is not large;4)The crustal structure in Wuhan is relatively stable,and the research results are in good agreement with previous studies.Therefore,this method can effectively analyze and detect the hidden faults in Wuhan,and then analyze the crustal structure in Wuhan.In summary,the multi-scale gravity inversion method used in this paper can effectively invert the crustal structure of Wuhan City,show its crustal density distribution,fault distribution form and Moho surface structure,and provide an idea for the study of urban crustal structure.It also provides an idea for the inversion of related geophysics.