南海北部陆坡崎岖海底区地震成像:OBS旅行时反演

深水陆坡油气资源丰富,是油气勘探的重要领域.由于陆坡水深变化较大、海底地形崎岖、地质构造复杂,地震成像存在诸多难点,其中,速度模型的建立是最大的难题之一.利用OBS(ocean bottom seismometer)数据上丰富的折射初至信息,采用旅行时反演方法建立崎岖海底区速度模型.OBS数据由广州海洋地质调查局在南海北部陆坡珠江口盆地东部海域采集,数据质量良好,存在大量的初至折射波.地震成像结果表明,在深水崎岖海底区,利用OBS的初至旅行时能够获得地震成像所需要的背景速度场.受限于高频近似的假设,初至旅行时反演结果分辨率较低.全波形反演可以提供精度更高的速度结构,初至旅行时反演结构可用作全波形反演的初始模型.

Seismic imaging of subsurface beneath rough seafloor in the north slope of South China Sea:OBS travel time inversion

The deep water zone has great oil and gas potential,and hence it is treated as key field of exploration.The great variation of water depth, the roughness of seafloor and the complex geological setting make it difficult to conduct seismic imaging of the target ob-ject.Velocity building is one of the greatest difficulties.The rich refraction wave in the OBS (ocean bottom seismometer) data was used to invert the velocity model with the method of travel time inversion.The OBS was acquired by Guangzhou Marine Geological Survey in the east part of Pearl River basin on the north slope of South China Sea.The OBS data have good quality with refraction wave clearly ob-servable.The imaging result shows that in the region of rugged seafloor, first arrival travel time inversion can provide the background ve-locity model needed by seismic imaging.Limited by the high frequency approximation,the velocity model has low resolution.More ad-vanced full waveform inversion can provide high resolution model,with first arrival travel time inversion result as the initial model.