Based on the analysis of the data on broadband ocean bottom seismographs deployed in the Northwestern sub-basin of the South China Sea from October 2019 to May 2020. We detected more than 150 000 short duration events （SDEs） at each OBS station by using STA/LTA algorithm. The characteristic of SDE signals is analyzed. According to different signal characteristics, these SDEs are classified as consecutive short duration events （C-SDEs） and random short duration events （R-SDEs）. The possible generation mechanisms for C-SDEs and R-SDEs are analyzed, respectively. We infer there are active sources of C-SDE signal in the Northwest Sub-basin of the SCS. The source may be caused by human activities, such as air gun firing or low frequency hydroacoustic communication signals. The R-SDE sources appear close to the OBS stations, likely generated by the ruptures due to gas escape from seafloor sediments. R-SDEs on OBS recordings indicate persistent gas escape from the sedimentary layer in the northwestern sub-basin of the SCS.