Characteristic reflector-based wave equation reflection traveltime inversion

Reconstructing the deep background velocity model is cru-cial for imaging subsurface structures. The reflection travel -time inversion (RTI) is capable of recovering the kinematic information in the velocity model under a limited seismic ob-servation aperture. The estimation of the reflection traveltime residuals between the synthetic and observed seismic waves is the key to the RTI. However, it is difficult to accurately obtain the rapidly changing reflection traveltime shifts in the prestack data domain. Estimating the traveltime difference is especially difficult where the discrepancy between the noisy observed data and demigrated synthetic data includes a waveform dis-tortion, inconsistent reflected events, and so on. To overcome this problem, we have developed a new reflection traveltime residual estimation method. In this method, after identifying a characteristic reflector in the prestack depth migration sec-tion with an initial velocity, the demigrated and observed seis-mic reflections in the data domain corresponding to the characteristic reflector share the same traveltime at the zero offset. Thus, their traveltime residual can be automatically tracked by their crosscorrelation with a modified dynamic pro-gramming algorithm based on a zero-offset control point, which can avoid traveltime picking or windowing of relevant reflection arrivals in the prestack seismic data domain. Then, the estimated reflection traveltime residual is applied to the RTI. To improve the inversion accuracy, we have further de-veloped a layer-stripping velocity model-building workflow. Synthetic and field data tests demonstrate that the proposed method can obtain a robust reflection traveltime residual and further achieve a correct low-to-intermediate wavenumber velocity model update.