Seismic heterogeneity and anisotropy of the Honshu arc from the Japan Trench to the Japan Sea
Seismic heterogeneity and anisotropy of the Honshu arc from the Japan Trench to the Japan Sea
复制标题
日本海沟至日本海本州弧的地震非均质性和各向异性
DOI：
10.1111/j.1365-246x.2011.04934.x
复制
发表时间：
2011-03-01
影响因子：
2.8
通讯作者：
Wang, Liangshu
中科院分区：
文献类型：
--
作者：
Huang, Zhouchuan;Zhao, Dapeng;Wang, Liangshu
从982个地震台记录的4655次局地地震资料中，我们确定了日本海沟至日本海底的本州弧的横波层析成像和横波各向异性结构。1451次海底地震的到达时间用深度相位重新定位，使我们能够确定太平洋和日本海下的构造，从而将研究区域从陆地区域扩大到从日本海沟到日本海的整个弧形，宽度超过500公里。研究结果表明，在太平洋板块下俯冲的太平洋板块上方具有很强的非均质性，在太平洋板块与上覆大陆板块耦合较强的高速区域，发生了较大的逆冲型地震。低速（低v）带成像于地幔楔，在火山锋下具有明显的沿弧变化。地幔楔低v带在日本海下向西延伸，与俯冲的太平洋板块在弧后下方150-200公里处相连接。结果表明，俯冲太平洋板块带下的水和流体通过脱水作用释放到地幔楔中，并通过地幔楔内的上升流输送到地表。本州弧下显示出显著的纵波各向异性异常。地幔楔以东西向为主，太平洋俯冲板块以南北向为主。地幔楔的各向异性是由于太平洋板块的俯冲和诱导的地幔-楔对流引起的形变，而地幔楔中部的FVD模式则认为是三维地幔流动或部分熔融地幔中橄榄石的特定排列。俯冲太平洋板块内的N-S（海沟平行）FVD既代表了太平洋板块形成时的原始化石各向异性，也代表了俯冲板块内由于板块弯曲而形成的海沟平行晶体学和形状优先取向。本研究结果对本州弧构造非均质性和地震各向异性有了新的认识，有助于提高对俯冲带动力学过程的认识。
SUMMARY We determinedP-andS-wave tomography andP-wave anisotropic structure under the Honshu arcfromtheJapanTrenchtothebackarcareaundertheJapanSeausing310749P-and150563 S-wave arrivals from 4655 local earthquakes recorded by 982 seismograph stations. Arrival timesfrom1451suboceanicearthquakesrelocatedwithsPdepthphasesenableustodetermine the structures under the Pacific Ocean and Japan Sea, which expand the study region from the land area to the whole arc from the Japan Trench to the Japan Sea with a width of more than 500 km. The results show strong heterogeneities above the subducting Pacific slab under the PacificOceanandmostlargethrust-typeearthquakesoccurredinthehigh-velocityareaswhere the Pacific slab and the overriding continental plate may be strongly coupled. Low-velocity (low-V) zones are imaged in the mantle wedge with significant along-arc variations under the volcanic front. The mantle-wedge low-V zone extends westwards under the Japan Sea and it is connected with the subducting Pacific slab at depths of 150–200 km under the backarc. The results indicate that the H2O and fluids brought downwards by the subducting Pacific slab are released into the mantle wedge by dehydration and are subsequently transported to the surface by the upwelling flow in the mantle wedge. Significant P-wave anisotropic anomalies are revealed under the Honshu arc. The predominant fast velocity direction (FVD) is E–W in the mantle wedge while it is N–S in the subducting Pacific slab. The anisotropy in the mantle wedgeistheresultofdeformationcausedbythesubductionofthePacificplateandtheinduced mantle-wedge convection, while the FVD pattern in the middle of the mantle wedge argues for the 3-D mantle flow or the specific alignment of the olivine in the partial-melting mantle. The N–S (trench-parallel) FVD in the subducting Pacific slab represents either the original fossil anisotropy when the Pacific plate formed or the trench-parallel crystallographic and shaped preferred orientation in the subducting slab due to the slab bending. The present results shed new light on the structural heterogeneities and seismic anisotropy under the Honshu arc, which may improve our understanding of the dynamic processes of subduction zones.