FULL WAVEFORM INVERSION

The inversion strategy proposed in this study is similar to Singh et.al.［4］.It is implemented in intercept time-slowness domain and consists of two steps.In the first step，long wavelength parts of velocity structure are estimated by very fast simulated annealing algorithm，which is a modified version of simulated annealing ing algorithm，and using travel-time information.In the second step，short wavelength velocity variations are derived by the conjugate gradient method，for which the inverted model is based on the initial model from the first step and using waveform information.The final inverted model consists of both long wavelength and short wavelength parts of the velocity structure.Our inversion is also a combination of a global search method and a nonlinear local search method.(https://www.daowen.com)

The inversion method combines travel-time inversion with waveform inversion，and global inversion with local optimum inversion together.Travel-time inversion is used to obtain the long wavelength information，and waveform inversion is for the short wavelength information.Global search method is used for the former problem with higher nonlinear characteristics，and local search method is for the latter problem with lower nonlinear characteristics.This is also unique practical way for present seismic waveform inversion as global inversion is time consuming and not practical for solving many model parameters.The synthetic seismograms are computed by the reflection and transmission matrix method［14］.The data for inversion is the transformed one in theτ-p domain from a CMP gather by plane-wave decomposition.Wavelet estimation，scaling and array correction should be considered in the inversion procedure.Very fast simulated annealing algorithm and the conjugate gradient method are described as follows.