Study On Active Faults Seismic Detection In The Urban Planning Area Of Xi'an

Xi'an area is located in the Weihe basin,the north is adjacent to ordos fault,the south is connected with the northern edge of the qinling orogenic belt.The two sides are uplifted to form the current Weihe faulted basin.This is one of the faulted basin in the edge of ordos block,which is very strong in the new tectonic movement.This special tectonic setting determines that the active faults in the Weihe faulted basin are relatively developed.Destructive earthquakes occur frequently in the place.And there are late Pleistocene faults and Holocene faults with the ability to generate large earthquakes.Historical earthquake disasters are particularly serious.The formation of earthquake disasters is closely related to the active faults in the area.It is important to study the shallow active fault seismic exploration in the region for scientific planning and construction in Xi'an area.Drilling is the most accurate method of active fault detection.However,due to the high costs of drilling and limited of drilling depth,shallow seismic exploration has become the most effective method for active fault detection.Due to the limitations of shallow seismic exploration principles,it is not possible to image formations with weak seismic reflection interfaces.Therefore,it is necessary to use trench exploration to determine the upper breakpoint of faults.Xi'an active fault exploration area is mainly for the city and its surrounding areas.The shallow seismic data has the following characteristics:weak excitation energy,long length of the survey line,large area of surface waves,strong environmental noise,and signal-to-noise ratio of field raw data.The resolution is low,and the active fault detection seismic profile requires high signal-to-noise ratio and resolution,which adds difficulty to seismic data processing.This article focuses on seismic data processing and fault location.The analysis and experimental studies were conducted around field data collection,static correction problems,signal-to-noise ratio problems,resolution problems,velocity analysis accuracy,and fault interpretation.In order to select the source of the active faults in the city,we first analyze the feasibility and effectiveness of various sources in the urban area,and select the appropriate source.Second,study the source excitation parameters to optimize the received raw data.For the problem of shallow seismic data statics,different models were first established to study the applicable conditions of various static corrections.Since the refraction static correction has a high requirement for the first-arrival wave,studying the refracted first-arrival pick-up pair can improve the accuracy of the refraction static correction.Then,use the actual data to compare and analyze the advantages and disadvantages of various static corrections.Selecting a reasonable static correction method for different near-surface conditions is particularly important.For the problem of SNR in shallow seismic data,first analyze the characteristics of the effective data and noise in the original field data.According to the features of noise in the different domain,targeted denoising methods are selected,and denoising tests and effect analysis are performed.The denoising effect is checked by the difference before and after denoising and the overlay profile.Integrate the advantages of different processing software modules together to improve the signal-to-noise ratio of shallow seismic data.For the problem of resolution of shallow seismic data,the appropriate deconvolution method was selected by analyzing and testing the advantages and disadvantages of various methods for improving resolution.Use the combined deconvolution method to increase the resolution of the data.In order to improve the speed analysis of seismic data with low SNR,in order to improve the accuracy of velocity analysis,the author proposes a denoising method for CMP gathers after dynamic correction,and performs wave field separation and filtering on the dynamically corrected gathers.You can remove those unleveled linear noises.The anti-noise of the gathers to do reaction correction,and then the speed analysis,this idea can effectively improve the superposition velocity spectrum in the energy group resolution and data signal to noise ratio.After fine processing of the seismic data,the reliability of the seismic profile will be greatly improved,and the obtained fault elements will be more reliable.It provides a reliable basis for the activity,risk,and harm of fractures in later research activities.