Study On Natural Source Surface Wave Prospecting Technology Based On SPAC

Surface waves account for 2/3 of the total energy in seismic waves,and have slow energy attenuation,high energy,and high signal-to-noise ratio.They spread in layered underground media.Using the dispersion characteristics of the surface wave,the local surface wave dispersion curve is calculated,and then the inversion is used to estimate the underground stratification,the thickness of each layer,and the lithology,so as to achieve the purpose of detection,and many geological problems can be resolved.Surface wave exploration is divided into artificial source surface wave exploration and natural source surface wave exploration.Its exploration depth is related to surface wave frequency.Artificial source surface wave exploration has a higher source frequency and lower energy.Generally,the deepest exploration depth does not exceed 30 m.Under certain unfavorable conditions,the depth of exploration is even less than 20 m,which often cannot meet the requirements.The natural source of surface wave exploration uses natural vibration,which has a low frequency,high energy,and a large depth of penetration,and can reach depths of several hundred meters to several kilometers.In engineering geophysical exploration,the high-frequency part of the natural source surface wave can be used to explore the depth range of about 30 m to 300 m.According to the depth of exploration and the surrounding disturbances,signals from several minutes to ten minutes can be collected at the same location.After calculating and processing,the dispersion curve can be obtained to estimate the stratigraphic structure.Natural source surface wave exploration is now the most commonly used spatial autocorrelation(SPAC)method and its derived extended spatial autocorrelation(ESPAC)method.The natural vibration meets the stochastic stochastic theory model.Based on this,the article bases on the spatial autocorrelation(SPAC)method and uses the matlab platform to compile the algorithm,which forms a set of natural source surface wave dispersion curve extraction procedures.Comparing the calculation method of the manual picking up special point with the fitting of the Bessel function of the-r based on the extended spatial autocorrelation method to extract the dispersion curve,it is proved that the expanded spatial autocorrelation method has high efficiency and accuracy High,exploration depth and other advantages.artificial source surface wave exploration was used at the same location.The comparative analysis of dispersion curves obtained from artificial source surface wave exploration and natural source surface wave exploration verified the reasonableness of natural source surface wave exploration and the accuracy of the program.In addition,data collected at the same location with different durations were processed separately.The results were compared.It was concluded that the longer the natural source surface wave exploration acquisition time is,the stronger the resistance to other noise interference is,and the more accurate the calculated results are.Finally,it puts forward the expectation of the observation system and program development of the combined exploration method of artificial source and natural source.