THE LEAST-SQUARES WAVEFORM INVERSION IN FREQUENCY DO-MAIN

The objective of this research is to obtain more subsurface lithologic information such as anisotropic,in-elastic parameters than onventional processing,by using the finite-element least-squares inversion in frequency domain,which is very helpful to direct detection or depiction of oil or gas reservoir, etc. Since to invert all the 1ithologic coefficients including anisotropic,inelastic directly is very nonlinear and difficult,we first select some sim-ple parameters to invert,such as P-wave and S-wave velocities,which can obtain more lithologic information:S-wave velocity than conventional acoustic-wave inversion.We deduce the formula of the finite-element least-squares inversion on the basis of forward modeling equations according to minimum of square roots of data residuals between field and calculation. We apply several advanta-genus methods,such as applying the compressional matrix-storage and LU-decomposition techniques to save and solve the large sparse complex-valued coefficient matrix,applying Green functions to solve the Jacobi coefficients in inversion fast,using the conjugate-gradient method to solve unknowns.