The Application Research Of OBS Seismic Data In The South Yellow Sea

OBS is a kind of seismic observation system which directly put the receiver onthe seafloor.When the internal clock begins to work, OBS starts to incessantly recordall kinds of signals around it. These signals contain ocean environmental informationsand seismic wave informations. According to different objects and study or differentpurposes of research, the means of analysis and application of these signals aredifferent. This thesis take the OBS seismic data of South Yellow Sea for example, andfocuses on the analysis, processing and application of typical signal. I hope thisresearch could help the scholars in the field go into more in-depth exploration.This paper contains of three parts:(1) Analysis and application of ocean ambient noise: The research objects of thispart are wind wave and swell. The viewpoint of statistics is used to analyze OBSwaveform and spectral characteristics of the far offset. Analysis area is divided intothe old swell stage, wind wave coming stage, wind wave stage, wind wave leavingstage and new swell stage. On the basis of different stages of duration time andextended length are calculated by the field seismic acquisition report, average velocityof ocean current around OBS in the seafloor could be calculated. In consideration ofthe climate and sea state conditions of the South Yellow Sea, the above phenomenonis thought to be due to the effects caused by southeast wind wave on the bottomcurrent. With the replacement of five stages, the energy of bottome current has seen achanges from low to high and then of a gradual decrease. Meanwhile, the swellenergy in this paper mainly strengthen the0~3Hz ocean ambient noise, the wind waveenergy is mostly to primarily influence the part of30Hz above, and both of themaffect the part of3~30Hz。(2) The South Yellow Sea OBS seismic data processing: The research object ofthis part is Seismic waves. By analyzing the noise and spectral characteristics ofpressure and vertical components, seismic waves are processed by the following procedures: true amplitude recovery, swell energy attenuation, frequency scanning todetermine the filter band, surface wave attenuation, the frequency, phase andamplitude matching of the pressure and vertical components, dual components mergeto attenuate ghost wave, random noise suppression, predictive deconvolution is usedto attenuate the multiple waves. Through dealing with the series of seismic dataprocessing for pressure and vertical component, some conclusions are as followssome conclusions are arrived at:①The effects of swell on the pressure and verticalcomponents are different. The swell energy of pressure component is so strong thatthe other seismic signals are covered. While in the vertical component, impact of theswell is not as obvious as the pressure component.②The distribution of noise isbounded in the direct wave. Outside of the region is relatively clean while inside ofthe region the noise waves such as surface waves, multiple waves are mutuallyinterference.③Before the merge of pressure component and vertical component, thematch of the frequency，phase and amplitude energy need to be completed. When thedata is combined, the ghost wave and reverberations will be attenuate correctly.④The data merge of dual components only can suppress ghost wave and reverberations.After data merge and random noise attenuation, the SNR of data be greatly improved.And then, the predictive deconvolution could be used to suppress multiple waves.(3) Analysis and application of OBS seismic data processing section: The objectof study is the seismic phase of the recorded data. On the basis of related materials athome and abroad, four seismic datas(C14,C16,C20,C22station) processing section isstudied, which obtains velocity and main phases information. The results shows:①The sections of four OBS stations are similar to the seismic section of adjacent serveyline on the structural characteristics of the crystalline basement (Pg phase). Itillustrates that in the case of known seismic phase veloctiy, the section could becorrected with constant velocity to achieve deep structure imaging;②The seismicprofiles of adjacent OBS stations can be complementary. Both of C14and C16OBSseismic sections involve the Quanliyan uplift and the Northern South Yellow SeaBasin depression. The influence of the direct wave area hampers the imaging of upliftand depression, so that the C14OBS seismic profile can be combined with C16to complete the seismic imaging of research area.③Author calculated the four OBSstations seismic data and gained the crust-mantle boundary information of the fourOBS stations.