Abstract:

The interval velocity and P velocity of seismic profiles A and B in the northern slope of the South China Sea were calculated by the methods of Dix equation and velocity inversion. The velocity characteristics of the gas hydrate bed were studied in detail based on the calculated results and the information，including BSR, amplitude blanking and polarity reversion of the waveform. It is shown that the higher velocity zone in the lower velocity background is an important characteristic of gas hydrate bed, and that the higher velocity zone usually parallel the seafloor, and that the velocity changes gradually in the higher velocity zone with the highest velocity at the center whereas the lowest at the margin, suggesting that the saturation of gas hydrate zone decreases gradually from the center to the margin. The study reveals that the high resolution velocity analysis is useful not only to search the hydrate spot but also to estimate the rich layer of gas hydrates.

Key words: the northern slope of the South China Sea, gas hydrate, seismic velocity, DIX equation, velocity , inversion