Seismic structure of western end of the Nankai trough seismogenic zone
Seismic structure of western end of the Nankai trough seismogenic zone
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DOI：
10.1029/2000jb000121
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发表时间：
2002-10
影响因子：
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通讯作者：
N. Takahashi;S. Kodaira;A. Nakanishi;Jin-Oh Park;S. Miura;T. Tsuru;Y. Kaneda;K. Suyehiro;H. Kinoshita;N. Hirata;T. Iwasaki
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文献类型：
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作者：
N. Takahashi;S. Kodaira;A. Nakanishi;Jin-Oh Park;S. Miura;T. Tsuru;Y. Kaneda;K. Suyehiro;H. Kinoshita;N. Hirata;T. Iwasaki
[1]1998年，利用气枪阵列和海底地震仪(OBSS)在日本西南部南海海槽孕育区的岸上-近海弧前区进行了320公里长剖面的地震试验。该地区位于1946年南海道8.2级地震同震破裂区之外。本文的主要目的是阐明日本西南部弧前区附近的P波和泊松比剖面，并估计该地区与南海道同震破裂区之间的差异。由二维射线追踪和走时反演得到的P波速度模型显示了三个具有不同速度模式的单元。透镜状单元最大厚度为5公里，速度为3.4-4.0公里/S，下伏单元速度为5.4-5.6公里/S，P波速度在陆地上增加(VP=6.2-6.4公里/S)。P波速度为6.6-6.9公里/S的相对均一单元位于P波速度为5.4-5.6公里/S的次级单元的正下方，俯冲角度为∼7°。我们还得到了弧前地区地壳结构的泊松比。次级单元南部的泊松比大于北部。我们的结论是，富含粘土的变质岩加上大洋玄武岩，而不是高孔隙度的物质，构成了该层的大部分。我们认为，泊松比高的区域可能对应于底侵和富粘土沉积物的变质作用，也可能对应于滑脱之下的大洋玄武岩。
[1] In 1998 a seismic experiment along a 320-km-long profile using an air gun array and ocean bottom seismographs (OBSs) was collected in the on shore-offshore, forearc region of the western Nankai trough seismogenic zone, southwestern Japan. This area is outside the coseismic rupture area of the 1946 Nankaido earthquake (Ms = 8.2). The main objectives of this paper are to clarify the P wave and the Poisson's ratio profile around the forearc region of southwestern Japan, and estimate differences between this area and the Nankaido coseismic rupture area. The P wave velocity model estimated by two-dimensional (2-D) ray tracing and travel time inversion indicates three units with distinctive velocity patterns. The lens-shaped unit has a maximum thickness of 5 km and velocity of 3.4–4.0 km/s. The underlying unit has velocity of 5.4–5.6 km/s, and its P wave velocity increases on land (Vp = 6.2–6.4 km/s). The relative homogeneous unit with P wave velocity of 6.6–6.9 km/s exists just beneath secondary unit with P velocity of 5.4–5.6 km/s. The angle of subduction is ∼7°. We also obtained a Poisson's ratio of the crustal structure of the forearc region. The Poisson's ratio of the southern part of secondary unit is larger than that of the northern part. We conclude that these data indicate clay-rich metamorphic rocks plus oceanic basaltic rocks, rather than high-porosity materials, comprise the majority of the layer. We suggest that the region of high Poisson's ratio probably corresponds to underplating and the metamorphism of the clay-rich sediments and possibly the oceanic basalt just below the decollement.