伍德拉克裂谷地区的海底地震仪方位和地壳结构  

Ocean bottom seismograph orientation and crustal structure of the Woodlark Rift

作　　者：高佳 于有强 Gao Jia;Yu Youqiang(State Key Laboratory of Marine Geology,Tongji University,Shanghai 200092,China)

机构地区：[1]同济大学海洋地质国家重点实验室,上海200092

出　　处：《地震学报》2023年第3期482-493,I0001-I0009,共21页Acta Seismologica Sinica

基　　金：国家自然科学基金面上项目(42074052);上海市青年科技启明星计划项目(22QA1409600);上海佘山地球物理国家野外科学观测研究站开放基金(2020K04)共同资助.

摘　　要：伍德拉克裂谷位于巴布亚新几内亚东南部,是发育在澳大利亚板块和西南太平洋板块碰撞带中的年轻大陆裂谷,为研究汇聚构造背景下裂谷起始演化的地壳结构提供了理想场所。伍德拉克裂谷海域地区海水层的存在使得获取高质量地震数据成为难题,而数据主要通过海底地震仪(ocean bottom seismograph,缩写为OBS)获取。OBS的布放一般是自由下落式,其地震计的北向水平分量方位与地理北向通常不一致,这使得利用三分量波形数据获取的反演结果产生了较大误差甚至失效,例如接收函数方法。为确定伍德拉克裂谷地区OBS水平分量的方位偏转角度,本文同时引入纵波和瑞雷面波偏振分析方法进行方位校正,并利用校正后的三分量波形数据开展接收函数研究,进而约束该裂谷海域地区的地壳结构。结果分析表明,OBS方位校正后,其获得的可用接收函数波形数量显著增多,并且利用纵波偏振分析校正后的数据处理获得了更加合理的地壳结构。基于在该裂谷地区获得的地壳构造结果,基里比斯盆地和裂谷扩张轴所在的古迪纳夫盆地呈现对比鲜明的地壳结构特征:古迪纳夫盆地的地壳厚度朝着裂谷扩张轴处减薄,其平均值为(33.3±2.42)km;基里比斯盆地的地壳厚度更薄,平均值为(24.1±5.44)km。此外,研究区域内所有OBS处均观测到了较高的地壳纵横波速比值,这可能是巴布亚超镁铁质岩体富集和古俯冲残片脱水熔融共同作用的结果。The Woodlark Rift in southeastern Papua New Guinea is a young continental rift and develops within the collision zone between the Australian and SW Pacific Plates,which offers an ideal location to explore the crustal structure beneath the incipient rift under a convergent setting.However,the sea water layer makes it difficult to collect high-quality seismic data,and the common step is to deploy the ocean bottom seismographs(OBSs)in a free-fall way.Therefore,mis-orientation of horizontal components of the OBS usually leads to failure of applying the inversion techniques such as the receiver function to the three-component waveforms.In this study,we employed both P-wave and Rayleigh-wave polarization analyses to determine all available OBS orientations,and then used the recorded teleseismic waveforms to conduct a receiver function study on the crustal structure beneath the Woodlark rift.The number of the receiver function traces has greatly increased after the orientation corrections and the crustal structures can be better constrained based on the results from P-wave polarization analysis.Contrasting crustal structures were revealed beneath the Kiribishi Basin and the Goodenough Basin where the rift axis is located.The crust beneath the Goodenough Basin is deciphered to thin towards the rift axis with an average of(33.3±2.42)km,while a much thinner crust is observed beneath the Kiribisi Basin with a mean value of(24.1±5.44)km.High vP/vS ratios were determined at all stations,which may be attributed to the Papuan ultramafic body and dehydration melting of fossil subducted slab segments.

关 键 词：伍德拉克裂谷 地壳结构 海底地震仪方位 接收函数 

分 类 号：P315.31[天文地球—地震学]