Study On The Method Of Q-Value Tomographic Inversion Of First-Arrival Wave Near Ground Surface

In areas with complex near-surface conditions(such as loess,desert,hill,etc.),quality factor Q is small,and the attenuation of seismic waves is serious,which results in the reduction of seismic resolution.The first arrival wave is the wave group which is the most easily identified and extracted in surface seismic data and has the highest signal to noise ratio.It has important wave field information.Therefore,it is particularly important to carry out accurate Q value tomography inversion in these complex near-surface areas.Therefore,it is imperative to accurately estimate the quality factor Q and perform attenuation tomographic inversion.Traditional methods of estimating Q value,such as amplitude attenuation method,spectral ratio method,and centroid frequency shift method,have their limitations,such as the dependence on the source wavelet,not suitable for the strong attenuation medium model,noise interference,etc.problem.In this paper,a Q value tomography method based on the first arrival wave near the surface is proposed,and the Q-value tomography equation without seismic source parameters is derived.(1)Because the near surface Q value is small and the velocity is low,the first-arrival wave has strong attenuation near the ground.In the case of strong attenuation,it generally does not satisfy the assumption that the spectral shape is a Gaussian function in the centroid frequency shift method.Therefore,in this paper,a formula for the extraction and attenuation parameters of any spectral shape and strong attenuation medium is derived.(2)Because of the noise interference in the seismic data,the high-frequency and low-band disturbances of the wavelet amplitude spectrum are strongly disturbed,and the stability of the attenuation parameter extraction depends on the selection of the integration frequency band.In this paper,the quantitative relationship between the error of the attenuation parameter extracted with noisy data and the signal-to-noise ratio of the selected frequency band is deduced,and the correction formula of the attenuation parameter with noise is given.(3)This paper obtains the minimum travel time and ray path by wavefront ray tracing by picking up and processing the first arrival wave information.On the basis of velocity tomography,combined with the new method for estimating the Q value deduced in this paper,the new method spectral ratio difference method derived the tomographic inversion equations.The first-order near-surface Q value tomographic inversion was performed.(4)In the end,near surface Q value tomography imaging,application and attenuation compensation are applied to the actual seismic data in the Loess area,confirming the feasibility and effectiveness of the proposed method,and greatly improving the resolution of seismic data from complex near surface seismic data.