NMO correction of long-spread seismic events in homogeneous and isotropic media
各向同性介质长偏移距地震同相轴动校正

The second-order Normal moveout equation is based upon two hypotheses. They are the small offset and simple straight-ray model. These hypotheses are invalid when seismic events with long-spread are processed. Normal moveout formulae with higher-order terms can improve NMO precision. In this paper, we compare several higher-order NMO formulae and propose optimal fourth-order NMO formula and optimal sixth-order NMO formula. The numerical computation results show that higher-order formulae can get better NMO output and the NMO precision is not improved with higher values of the maximal order at all time. if vertical velocity gradient is strong. None of the formulae can achieve satisfying NMO result when the ratio of maximal offset to objective depth is more than 3.5. Optimal fourth-order and optimal sixth-order formulae are more steady and more precise and more appropriate for field seismic data processing because the influence of infinite offset is corrected in those formulae.