CONCLUSIONS

It is difficult for conventional velocity analysis and amplitude analysis to distinguish between the gas hydrate wedge model from free gas zone model［9］，then investigate the origin and nature of BSR.The full waveform inversion interpret exactly the reverse polarity of the double BSRs，and give high-resolution velocity structure，and can be used for studying the distribution of gas hydrate-bearing sediments and free gas-bearing sediments.

Because the double BSR may indicate a rapid evolving gas hydrate system，it has received much attention.Usually there are two potential explanations for the second BSR［19］.First，it can be explained to be a paleo gas-hydrate BSR，a reflection from the base of gas hydrate stability zone of a former set of pressure and temperature conditions.Second，it can be explained to be a reflection from the base of gas hydrate bearing sediments with a different gas composition than simple methane hydrate.The distribution of gas hydrate layers and free gas layers derived from our inversion result can be combined with other geological and geochemical data to discuss which explanation is more reasonable.(https://www.daowen.com)

A full waveform inversion from single component seismic data is presented and can give the distribution feature of single parameter，P-wave velocity.Inversion from multi-component seismic data can distinguish S-wave velocity and density well［20～22］，and three-component wide-angle data have been and are being acquired by ocean bottom seismogram on some continental margins.It is predicted that full waveform inversion of multi-parameter will become an important tool for gas hydrate research.The study of the full waveform inversion of gas hydrate BSR is preliminary and further research of the inversion method and its application is under way.