A detailed subduction structure in the Kuril trench deduced from ocean bottom seismographic refraction studies
A detailed subduction structure in the Kuril trench deduced from ocean bottom seismographic refraction studies
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根据海底地震折射研究推导出千岛海沟的详细俯冲结构
DOI：
10.1016/0040-1951(89)90056-5
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发表时间：
1989
期刊：
影响因子：
2.9
通讯作者：
H. Shimamura
中科院分区：
文献类型：
--
作者：
T. Iwasaki;H. Shiobara;A. Nishizawa;T. Kanazawa;K. Suyehiro;N. Hirata;T. Urabe;H. Shimamura
1983年，我们在千岛海沟的最南端进行了海底地震仪（OBS）实验，太平洋板块正俯冲到日本北海道岛下方。该实验的目的是通过使用炸药和气枪的密集地震折射剖面来确定从洋盆到大陆坡的地壳和上地幔结构。剖面总长度为 560 公里，沿线部署了 10 个 OBS。观测数据质量良好，使我们能够获得活动边缘低至20-30公里的详细速度结构。我们通过射线追迹和振幅建模建立了速度结构模型。在大洋盆地中，地壳具有典型的三层海洋结构，纵波速度分别为1.8、3.8~6.5和6.5~7.0 km/s。第 3 层的速度梯度从 0.075 向下增加到 0.10 s−1。莫霍面不连续性受到清晰观察到的 Pn 和 PmP 相位的良好约束。洋壳的总厚度经确定为 8 公里，并且在大洋盆地中几乎恒定。莫霍面不连续面下方的 P 波速度为 7.9 km/s，以相当小的速度梯度（0.015-0.03 s−1）向下增加。在大陆坡下方，我们发现了速度相对较低（2.5 至 5.5-5.8 公里/秒）的物质。与俯冲板块相关的海洋莫霍面不连续性可追溯到 25 公里的深度。我们的地震数据强烈表明，大洋第 2 层正在平稳地俯冲，不会破裂形成楔形结构。这一结果与琉球海沟区域活动边缘（距本实验区以南约 1000 公里）的速度结构形成鲜明对比，我们在琉球海沟区域发现了一个 12 公里厚、突出的低速楔子，位于距海沟轴线向陆 50-150 公里处。在楔子的临海一侧，火成岩基底的表面起伏剧烈。该楔子可能是由海洋来源的材料形成的。这种速度结构的差异表明西北太平洋海沟区域的俯冲机制因地区而异。
In 1983, we conducted an ocean bottom seismograph (OBS) experiment in the southernmost part of the Kuril trench, beneath which the Pacific Plate is subducting under Hokkaido Island, Japan. The aim of this experiment was to determine crust and upper mantle structure from the oceanic basin to the continental slope by dense seismic refraction profiling, using explosives and airguns. The total length of the profiles was 560 km, along which ten OBS's were deployed. The observed data were of good quality, which enabled us to obtain a detailed velocity structure of the active margin down to 20–30 km. We constructed a velocity structure model by ray-tracing and amplitude modeling.In the oceanic basin, the crust has a typical oceanic structure characterized by three layers with P-wave velocities of 1.8, 3.8–6.5 and 6.5–7.0 km/s. The velocity gradient in layer 3 increases downward from 0.075 to 0.10 s−1. The Moho discontinuity was well constrained by clearly observed Pnand PmP phases. The total thickness of the oceanic crust was determined to be 8 km and almost constant in the oceanic basin. The P-wave velocity is 7.9 km/s beneath the Moho discontinuity, which increases downward with a rather small velocity gradient, 0.015–0.03 s−1. Beneath the continental slope, we found relatively low velocity (2.5 to 5.5–5.8 km/s) material. The oceanic Moho discontinuity associated with the subducting plate was traced down to a depth of 25 km. Our seismic data strongly suggest that oceanic layer 2 is smoothly subducting and does not break up to form a wedge structure. This result is in remarkable contrast with the velocity structure in the active margin of the Ryukyu trench area (about 1000 km south of the present experimental area), where we found a 12 km-thick, prominent low-velocity wedge is situated 50–150 km landward from the trench axis. On the seaward side of the wedge, the surface of the igneous basement undulates severely. The wedge was probably formed by materials of oceanic origin. Such a difference in velocity structure suggests that the subduction mechanism in the trench area differs from region to region in the northwestern Pacific.