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为了研究九州—帕劳洋脊(KPR)俯冲部分与同震破裂扩展、地震活动性和浅部甚低频地震的关系,对南海海槽西部俯冲带日向滩地区进行了三维地震层析成像。结合岸上和近海记录的主动源和被动源地震数据,成像了从该海槽轴附近到海岸地区的深部板块。我们的结果表明,俯冲的九州—帕劳洋脊为西北—东南向的低速带,向下扩展到约30km的深度。在这个深度,我们认为俯冲的九州—帕劳洋脊与板块分离,成为上覆大陆板块的底座。由于过去大地震的同震滑动地区没有延伸到俯冲的九州—帕劳洋脊,我们认为九州—帕劳洋脊可能阻碍了破裂的扩展。俯冲的九州—帕劳洋脊的内部在很宽的深度上分布有活跃的板内地震活动。浅部甚低频地震在俯冲的九州—帕劳洋脊上部连续发生,而在俯冲的九州—帕劳洋脊的东北部却是间歇地出现。因此,俯冲的九州—帕劳洋脊看来是这个地区同震破裂扩展和地震现象的一个重要因素。
In order to study the relationship between the subduction of Kyrgyz-Palau ridge (KPR) and the co-seismic rupture expansion, seismic activity and shallow and very low frequency earthquakes, a three-dimensional seismic tomography imaging of Rixiangtan subduction zone in the west of the South China Sea Trough was conducted. Combining the active and passive source seismic data recorded onshore and offshore, the deep plate from near the trough axis to the coast is imaged. Our results show that the subducted Kyushu-Palau ridge is a northwest-southeast low-velocity belt that extends down to a depth of about 30 km. At this depth, we believe the subducted Kyushu-Palau ridge separates from the plate and becomes the base of the overlying continental plate. Due to the unconverted Kyushu-Palau ridge caused by the coseismic slip of the past earthquakes, we believe that the Kyushu-Palau ridge may hinder the expansion of the rift. The subducted Kyushu-Palau ridge has active intraplate seismic activity distributed over a wide depth. Shallow and very low frequency earthquakes occur continuously above the subducted Kyushu-Palau ridge, intermittently in the northeastern subducted Kyushu-Palau ridge. Therefore, the subducted Kyushu-Palau ridge appears to be an important factor in the expansion of the coseismic expansion and seismic phenomena in this area.