ANALYSIS AND PROCESSING OF ABNORMAL OBS DATA IN THE SOUTH CHINA SEA

Processing and analysis of ocean bottom seismometer (OBS) data are of great importance to obtain the deep crustal structure. The deep seismic profile OBS2006-2 was carried out in 2006 along the extinct spreading ridge of the northwest sub-basin of the South China Sea. This survey is successful to provide high quality data whose seismic signals can be observed at the offset up to 120 km, but 2 OBSs’ recording data (OBS03 and OBS06) cannot be read correctly and were not used in later structure modeling. However, OBS data are very precious due to the high cost and arduous work. The price is more expensive when encountering severe weather during a survey. This paper is focused on reprocessing of these 2 OBSs’ data by use of the methods of checking data format, comparing signals with adjacent OBSs and resampling the data. Finally we acquire these 2 OBSs’ seismic record sections in which abundant seismic phases are clearly seen. We also obtain the seismic record section of OBS03 along the profile OBS973-3 in the Nansha Island using the same methods above. The instrument OBS06 along the profile OBS2006-2 and the instrument OBS03 along the profile OBS973-3 are the same instrument confirmed by checking their logs recorded in 2006 and 2011, respectively. It demonstrates that the processing method for abnormal OBS data is reliable and effective. Then the ray-tracing and travel-time simulation were carried out for OBS06 and OBS03 using the interactive trial-and-error 2D ray-tracing method based on the previous P-wave velocity model of OBS2006-2. The input of new travel-time picks should provide stricter constraints for the deep structure beneath the profile OBS2006-2. This research on abnormal data reprocessing does not only improve the reliability and resolution of the crustal structure, but also provide valuable experiences for OBS processing for other study areas in the future.