【摘要】 置于海底数百米至数千米的海底地震仪(OBS)的实测信号相比陆地地震仪具有不同的特性;由于水的作用或记录信号源频率的不同,短周期OBS和宽频带OBS记录的信号又有明显的差异。文章对南海西南次海盆地震探测期间记录的人工气枪震源和天然地震实测信号进行了时频分析,结果如下。1)气枪作业后在海底激发两种噪声:一是水的波动不断叠加形成的长波,周期50s左右,以水平分量为主;二是高频噪声,主要是OBS底座细微晃动引起的。2)宽频OBS对于水下移动目标激发海底波动具有很好的探测能力,特别是水平分量可以获得大振幅且周期特征清晰的记录,并能够指示方向。3)宽频OBS能记录到清晰的天然地震信号,为研究调查区岩石圈结构增添了更多的信息,短周期OBS对远震直达P波有很好的记录。国产宽频I-4C型OBS碰巧记录了日本M9.0级大震。更多还原

【Abstract】 Seismic signals of ocean bottom seismometer(OBS) on the seafloor hundreds or thousands meters deep are different from those of land seismometer.The records of short-period OBS are also obviously different from those of broad-band OBS due to effects of sea water or signal frequency.This study carried out time-frequency analysis and compared the seismic signals excited by air gun as well as earthquake signals of OBS during a seismic survey in the southwest sub-basin of the South China Sea.The results are as follows.1) Air-gun shooting generated two kinds of noises: one is long-wave noise due to the superposition of water fluctuation,with a period of 50s mainly in the horizontal component;the other is high-frequency noise,mainly due to fin vibration of OBS pedestal itself.2) Broad-band OBS is able to detect the fluctuation caused by moving object under water,especially in the horizontal component whose amplitude is large and whose frequency feature is clear,from which the direction of the signal source can be distinguished.3) During this survey broad-band OBS recorded many high-quality earthquakes that will benefit our study on the lithosphere structure of the survey area,while short-period OBS had also obtained direct P-wave arrivals clearly.The I-4C type OBS happened to record the catastrophe earthquake of M9.0 occurred near Japan in March 2011.更多还原