Research On Q Value Tomographic Inversion Method Based On First Break

Attenuation tomography is an important method for the inversion of Q value.It has great theoretical meaning and application value to understand the principle of tomography and analyze the influence factors of imaging accuracy.This paper studies the numerical simulation of the first break attenuation tomography,and analyzes the influencing factors of the inversion results by taking model data and field data as examples.In the theoretical research and numerical simulation part,the ray tracing forward modeling are conducted based on fast marching method(FMM)in the first place.The FMM ray tracing forward modeling uses the upwind finite difference and narrowband techniques to calculate and update the travel time at each grid node.This method has the characteristics of unconditional stability,meanwhile its expansion pattern conforms to the wave-front propagation law.Secondly,the tomography inversion method based on spectral-ratio method and least-squares QR decomposition method(LSQR)are studied.The spectral-ratio method can calculate Q value stably,and LSQR is an effective algorithm for solving large sparse linear equations.Compared with other inversion methods,it’s more suitable for solving ill-posed problems.In this paper,the numerical simulation of attenuation tomography based on first break is accomplished by using the mentioned two methods,and good inversion results are obtained.In the field data test and influence factors analysis part,4 effects on the inversion results are studied.Especially initial model and number of iterations are analyzed based on the field data test results.The research results illustrate that the more accurate the velocity model is,the higher accuracy of ray tracing forward modeling and Q value inversion have.As the numbers of iterations increase,the accuracy of the inversion results gradually increases and tends to be stable.