Application Of Seismic Interference Imaging Technology In Shallow Exploration

With the rapid development of Chinese cities in recent years,the use of shallow underground space is increasingly needed,so it is urgent to master the geological structure of shallow underground space.Due to the complex geological conditions in shallow strata,it is difficult to obtain the reflected wave field directly,and the weak seismic signals of poor geological bodies such as goaf and karst cave are weak.Conventional seismic imaging methods are difficult to obtain better imaging or weak seismic positioning in underground space.Seismic interferometry can reconstruct the underground wave field by cross-correlation processing,which solves the difficulty of obtaining the reflected wave field and imaging the weak motion in space.In this thesis,the theory of interferometric imaging of active and passive sources is derived in detail,and a variety of geological models are constructed.The feasibility and influencing factors of interferometric imaging of active and passive sources are analyzed by acoustic wave and elastic wave numerical simulation respectively.Finally,this method is applied to two actual data,and the application results show that the seismic interference imaging technology can better realize the imaging of shallow surface structures and goaf.Firstly,the principle of seismic interference technique is studied,this thesis after time migration of the green's function of recording and when the source and detector in the target surface of rock mass is similar to the data,pointed out that the principle of seismic interference is the wave field cross-correlation between any two detector for the seismic response between the two detector,prove time transfer and time domain cross-correlation are equivalent,and respectively introduces the active and passive interference imaging sources of interference imaging in physics meaning.Secondly,models of horizontal interface,single inclined interface and undulating interface were established.Wave field characteristics were analyzed based on numerical simulation of acoustic wave and elastic wave,and imaging of underground structure was achieved by using active source interference imaging method.The imaging results were consistent with the undulating state of the model interface.In addition,the influences of wavelet types,frequency sizes and track spacing parameters on interferometric imaging were analyzed,and the following conclusions were drawn:Among the three types of single,double and Ricker wavelet,Ricker wavelet has the characteristics of high resolution;With the increase of excitation frequency,the resolution of common offset trace sets becomes higher,but the explorable depth also decreases gradually;With the increase of track spacing,the path spacing has the characteristics of high resolution under the same model size,but the size of track spacing has little effect on the travel time of the extracted reflected wave.Then,through the establishment of a single uniform model,a two-dimensional complex model and a dual source model,the source location was carried out based on passive source interference imaging technology to verify the applicability of passive source imaging to a variety of models.Through the comparative analysis of the migration imaging results,it is found that:(1)There is little error between the migration imaging results of the single uniform model and the two-dimensional complex model and the actual one.(2)The lateral resolution of passive source interferometer imaging is higher than the vertical resolution,and different migration velocities have almost no effect on the lateral location,but the vertical position has a greater effect.Finally,the seismic interferometric imaging technology is applied to the actual data,and the actual data of a region in Xuzhou is collected.The primary reflection wave is reconstructed from the refracted multiples to synthesize a new channel set to judge the undulated state of the underground interface.Taking passive source data from a mine in Shanxi Province as an example,the imaging results are consistent with the reality.