A Study Of Seismic Interferometry Based On Stationary Phase Theory And S Transform

In recent years,seismic interferometry has become a research hotspot in geophysics field.The study and its development have expanded people's understanding of the seismic wave propagation law.With the basic thought of calculating the Green's function between both according to the cross-correlation of two geophone records,seismic interferometry can be divided into passive source interferometry with background noise as the research object and active source interferometry with artificial seismic source as the research object according to different hypocenter types.This paper is mainly focused on the virtual source method of active source interferometry from the perspective of the reconstruction of hypocenter base level,as well as the reduction of the interference of the complex superstratum.The impact of the complex superstratum on the seismic wave field is one of the common issues in seismic exploration.Seismic waves passing through the overlying layer with severe changes will deform and scatter strongly.To solve the complex overlying structure problem,Virtual Source method can be used to reset focal point to geophone positions under the overburden and redefine the focal datum level,thus eliminating the influence of the overlying layer on the seismic wave and enhancing imaging accuracy.In this paper,the basic principles of seismic interferometry are reviewed firstly,direct wave and reflected wave interference are described intuitively and the Green's function expressions under different seismic source conditions such as pulse source,wavelet source and noise source are discussed.Then,this paper introduces the Green's function theory in the seismic interferometry,and derives the basic equation of the seismic interferometry—the correlation reciprocity equation.Finally,according to the far field approximation theory,the basic equation of seismic interferometry is simplified.The model results of acoustic wave field show that virtual source method is feasible and advanced in the application of complex near surface exploration.In addition,the influence of different observation system factors on seismic interferometry imaging is also discussed,and the results show that the quality of reconstructed records gradually deteriorates with the increase of source distance and trace distance.Since the actual observation system cannot meet the theoretical requirement of intensive sampling of shots around the receivers,the seismic interferometry will produce different degrees of false noise when reconstructing records.To solve this problem,based on the theory of stationary phase,this paper proposes a weighting algorithm for the cross-correlation map and the corresponding superimposed trace.The energy at the stable phase point is directly extracted from the cross-correlation map and superimposed to eliminate the energy of non-stable phase point caused by the limitation of the observation system.The energy interference of the phase stabilization point improves the quality of the reconstructed record.In addition,in order to solve the problem of low SNR of seismic records due to the influence of noise in the reconstruction of seismic interferometry in the time domain,this paper proposes a research idea of combining seismic interferometry and S-transform to suppress noise and improve the SNR of reconstructed records.Model tests and practical application results show that compared with the traditional time-domain interference,the method in this paper obtains a reconstruction record with a higher SNR.