| 西北太平洋俯冲带大地幔楔及地幔过渡带各向异性证据和特征 |
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| 引用本文： | 郭广瑞,李娟,陈思丹,Walter D.Mooney.西北太平洋俯冲带大地幔楔及地幔过渡带各向异性证据和特征[J].地球物理学报,2021,64(2):455-470. |
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| 作者姓名： | 郭广瑞 李娟 陈思丹 Walter D.Mooney |
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| 作者单位： | 中国科学院地质与地球物理研究所,北京100029;中国科学院大学,北京100049;中国科学院地质与地球物理研究所,北京100029;中国科学院大学,北京100049;漠河地球物理国家野外科学观测研究站,北京100029;美国地质调查局,CA 94025 |
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| 基金项目： | 国家自然科学基金;美国地质调查局地震灾害项目资助;国家重点研发计划"重大自然灾害监测预警与防范"重点专项 |
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| 摘 要： | 地震层析成像研究清晰给出了地球深部俯冲板片的大尺度形态,但与俯冲过程相关的地幔流动特征仍不明确.在俯冲地幔楔系统中,前人观测到了与海沟平行和垂直的快波偏振方向.本文研究了西北太平洋俯冲板片在地幔过渡带中停滞形成的"大地幔楔"中的各向异性特征.对具有长期稳定观测数据的MDJ台站SKS震相和区域深源地震的直达S波震相进行了详细的剪切波分裂研究.采用多波形同时反演方法在保证数据后方位角覆盖范围的基础上得到了更加精确的SKS震相各向异性结果.剪切波分裂参数具有明显的频率依赖性和随初始极化方向变化的特征,表明台站下方存在多个可能的各向异性源区.对不同频段各向异性观测结果的双层各向异性模型拟合表明,上层各向异性参数为φ=32°±12°,δt=1.4±0.4 s,表现出受郯庐断裂带影响的岩石圈中"固化"各向异性特征;下层各向异性参数为φ=-71°±6°,δt=2.4±0.4 s,与海沟近乎垂直.下层较大的各向异性延时表明研究区域的地幔楔和地幔过渡带中存在明显各向异性,推测是由地幔中软流圈流动引起的橄榄石晶格优势取向和停滞的西北太平洋板片引起的地幔水平流动产生的瓦兹利石晶格优势取向共同作用所导致.
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| 关 键 词： | 各向异性 剪切波分裂 大地幔楔 地幔过渡带 频率依赖性 双层各向异性模型 多波形同时反演 |
Seismic anisotropy in the big mantle wedge and mantle transition zone of the northwestern Pacific subduction system |
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| GUO GuangRui,LI Juan,CHEN SiDan,Walter D.Mooney.Seismic anisotropy in the big mantle wedge and mantle transition zone of the northwestern Pacific subduction system[J].Chinese Journal of Geophysics,2021,64(2):455-470. |
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| Authors: | GUO GuangRui LI Juan CHEN SiDan Walter DMooney |
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| Affiliation: | (Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China;University of Chinese Academy of Sciences,Beijing 100049,China;Mohe National Observatory of Geophysics,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China;United States Geological Survey,CA 94025,USA) |
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| Abstract: | The morphologies of subducting slabs have been clearly imaged by seismic tomographic techniques,however,the character of the mantle flow associated with subduction process remains ambiguous.Both trench parallel and trench normal patterns of seismic anisotropy have been reported in various mantle-wedge subduction systems.Here we investigate the anisotropic characteristics in the“Big Mantle Wedge”that is formed by the stagnation of the subducting Pacific slab.A detailed shear wave splitting study was conducted on the SKS phase and the direct S-wave phase of regional deep-source earthquakes of MDJ station,which has a long-term stable observation data.Simultaneous multi-waveform inversion(SIMW)method is used to obtain more accurate SKS phase anisotropy results on the basis of guaranteeing the azimuth coverage.We identified prominent frequency dependence and initial polarization variability in apparent splitting parameters,indicating the presence of multiple possible sources of anisotropy.Two-layer anisotropic model fitting based on the SIMW results in different frequency bands shows a trench-oblique fast direction ofφ=32°±12°,δt=1.4±0.4 s in the upper layer,attributed to the fossil anisotropy in the lithosphere affected by the Tan-Lu fault zone.And a nearly trench-normal fast direction ofφ=-71°±6°,δt=2.4±0.4 s in the lower layer.The large delay time in the lower layer indicates the presence of anisotropy within the mantle transition zone and possibly deeper.The trench-normal fast axis direction may be due to the combined effects of the lattice preferred orientation(LPO)of olivine caused by asthenosphere flow in the shallow mantle,and the LPO of wadsleyite caused by the lateral mantle flow associated with the stagnation of the Pacific slab. |
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| Keywords: | Anisotropy Shear wave splitting Big mantle wedge Mantle transition zone Frequency dependence Two-layer anisotropy model Simultaneous multi-waveform inversion(SIMW) |
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