| With the increasing progress of engineering exploration technology,the engineering exploration level is also facing a huge challenge.Compared with other exploration methods,passive source exploration method is not only flexible in field layout and simple in acquisition,but also can extract lower frequency information after long time observation,and can detect deeper strata structure.Passive source mainly includes wind and grass moving,vehicle movement,construction and natural tsunamis,earthquakes,volcanic eruptions and other natural vibration.These natural vibrations contain abundant information of low frequency surface waves,which propagate outwards in the form of waves and are mainly composed of surface waves.The numerical simulation method is widely used in seismic wave field simulation.Therefore,it is feasible to simulate the wave field of background noise.By studying the background noise,seismic exploration scholars find that the structure of subsurface velocity layer can be retrieved by extracting the dispersion curve of the background noise.Most researchers use the actual data to extract dispersion curves to invert the underground structure.In this paper,by analyzing the research background noise signal parameters(the number of source,coordinates,and the size of the delay time,dominant frequency and energy,wavelet type and the source direction of loading,etc.)of randomness and diversity,the way of geophone array based on elastic wave equation,and the numerical frequency dispersion,stability conditions,the source loading and boundary conditions and so on made a contrastive analysis of the concrete,The finite difference wave field numerical simulation method is used to obtain the seismic records and wave field snapshots of the velocity components of the background noise.Based on the numerical simulation of the background noise wave field,the superposition response of the detector is preprocessed by filtering,and the spatial autocorrelation method(SPAC)and Aki method are used to extract the surface wave information for spectrum analysis,and the dispersion curve of the random seismic source is compared with the theoretical dispersion curve obtained by the dispersion equation.In this paper,the feasibility and effectiveness of the proposed method are further verified by establishing low speed and high speed two-layer models,three-layer models with low speed layers and four-layer models with low and high layers,which provide a powerful theoretical basis for the imaging results of passive sources and important evaluation parameters for geophysical and geological disaster prevention. |
