南海北部陆缘OBS2018–H2测线地壳结构初步结果

Preliminary results of the crustal structure along OBS2018-H2 in the northern continental margin of the South China Sea

南海北部陆缘洋陆转换带实施的OBS2018–H2测线的地壳速度结构,将为探讨南海张裂-破裂机制提供重要证据。文章介绍了OBS2018–H2测线前期数据处理流程,包括多道反射地震数据处理、海底地震仪OBS(Ocean Bottom Seismometer)数据格式转换、炮点和OBS位置校正,以及OBS震相的初步识别,并对地壳结构进行了初步分析。结果表明:炮点和OBS位置校正效果良好;多道反射地震数据为建立初始速度模型提供了良好约束;OBS综合地震剖面识别了多组清晰的P波震相,包括Pw、Pg、PmP和Pn震相。根据测线西侧OBS36、OBS37两台站的震相分布特征初步估算台站下方地壳厚度约为6~7km,与根据多道地震剖面LW3的双程走时估算的厚度6~9km大致相符。

The crustal velocity structure along profile OBS2018-H2 located in the continent–ocean transition can provide important evidence for the rifting-breakup mechanism of the northern margin of the South China Sea(SCS).The preliminary data processing steps are presented in this paper,including multi-channel reflective data processing,OBS(Ocean Bottom Seismometer)data format conversion,shot and OBS relocation,and identification of OBS seismic phases,followed by a preliminary analysis of the crustal structure.Our results show that relocations of shots and OBSs are effective and reliable.The multi-channel seismic(MCS)profile provides a good constraint for building the initial velocity model.Several groups of seismic phases,e.g.,Pg,PmP and Pn,are clearly identified in OBS comprehensive seismic profiles.Based on the distribution characteristics of the OBS36 and OBS37 seismic phases on the west side of OBS2018–H2,the thickness of the crust below these two stations is estimated to be about 6~7 km.It is roughly equivalent to the thickness of 6~9 km estimated from the two-way travel time in MCS profile LW3.