南海海盆地震活动性监测与研究

南海中央海盆于2019年9月5日突然发生了一次Mw5.4级地震。此中强地震的原因、孕震构造和动力学机制、后续地震活动性、对海底生态、地质环境的影响亟待研究和评估。此地震震中位置很特殊，位于“中南断裂”与中央海盆残留扩张脊走向转折区的交汇处，也是海底地震（OBS）主动源地震剖面所圈定的破碎带边界上, 因此，它的后续地震活动（微震）为研究海盆地壳/地幔深部结构、断裂性质、海底扩张机制提供了一个上佳的窗口和新数据源。震后我们已及时投放了5台宽频带OBS对地震活动性进行了监测。本申请计划再开展1～2期的监测，结合前期的主动源速度模型和数据，采用微震定位、波形频率分析、接收函数反演、各向异性计算等方法，精确确定主震深度和错动方向，研究后续地震活动性和影响、力学机制与应力场特征及断裂构造的关系，进而研究海盆残留扩张脊深部构造、转向、连续性问题、“中南断裂”的性质和作用，探讨海底扩张过程和机制。

On September 5，2019 an earthquake with magnitude Mw 5.4 suddenly occurred in the quiescent central basin of the South China Sea. We think it is necessary and urgently to study this middle strong earthquake occurrence reason, focus geo-tectonics, dynamics and seismic activity developing tendency, and to estimate its influences on submarine biological and geological environment. On the other hand, since its hypocenter is located at the cross point of “Zhongnan Fault” with direction turning place of the residual seafloor spreading ridges, also coincident with fracture boundary determined by previous OBS active seismic model, its following seismic activity(micro-earthquakes) would provide us with a good window and new data source for study of the basin crust and deep mantle structure, faults features and seafloor spreading mechanism. Fortunately, we have deployed five OBSs in time around the hypocenter for monitoring seismic activity. The new suggested proposal also plans to continue this monitoring with 1-2 times observation. Then based on previous active seismic velocity model and raw data, adopting methods such as micro earthquake locating, waveform and frequency analysis, receive functions, anisotropy approach, we intend to use the new seismic activity monitoring data to relocate the main earthquake depth and fault slide direction, micro earthquakes and their influences on submarine environment and the main earthquake occurrence dynamics and its relation with stress filed and fault systems. Furthermore, the residual ridge deep structure，ridge extending direction changes and its continuity, and the characteristics and roles of “Zhongnan Fault” are going to be studied for profoundly discussing the SCS formation process and mechanism.