Abnormal data missing and internal time correction of Ocean Bottom Seismometer

During cruise TS03 in the Southern Mariana Trench, a series of active and passive seismic surveys were carried out using Ocean Bottom Seismometer (OBS) produced in China, aiming at cross-trench crustal structure and local seismicity. However, abnormal direct-water-wave events were found on the seismic section of POBSO4, and a large GAP between data files was also noticeable during data processing. These abnormal data bring uncertainty to the following relocation of OBSs and seismic tomography. To analyze these abnormal data, arrival times of direct water wave were calculated and then compared with the air-gun signals in SAC file. Our results show that the internal time of POBSO4 was incorrect because of data missing, which then resulted in early arrival of air-gun signals. Based on these findings, we delayed the arrival time of air-gun signals in SAC software to be identical to calculated arrival time of direct water wave. After that, correct SEGY file can be converted and plotted. This study reveals a new kind of abnormal data. This procedure assists in OBS relocation and seismic tomography, and provides new references for abnormal data correction and OBS upgrade.