Along-arc structural variation of the plate boundary at the Japan Trench margin: Implication of interplate coupling
Along-arc structural variation of the plate boundary at the Japan Trench margin: Implication of interplate coupling
复制标题
DOI：
10.1029/2001jb001664
复制
发表时间：
2002-12
影响因子：
--
通讯作者：
T. Tsuru;Jin-Oh Park;S. Miura;S. Kodaira;Y. Kido;Tsutomu Hayashi
中科院分区：
文献类型：
--
作者：
T. Tsuru;Jin-Oh Park;S. Miura;S. Kodaira;Y. Kido;Tsutomu Hayashi
[1] 日本海沟辐合边缘经常发生M7.5级以上的大板间地震。震中分布不均，主要集中在北部地区。为了研究这种分布与构造结构之间的关系，我们自1996年以来进行了多道地震勘探。我们的数据显示了两种板间沉积单元：楔形单元和通道状单元。两个单元的 P 波速度均低于上覆岛弧地壳的基底部分。速度为2~3 km/s的楔形单元广泛分布于北部弧前区。它的厚度随着深度的增加而减小，在~12公里深度处厚度达到数百米。南部地区观察到速度为3~4 km/s的通道状单元，沿下倾方向延伸。其厚度在~12公里深度处达到~2公里。如果这些单元的低速度是由于流体的存在而导致的，正如许多作者假设的那样，那么假设孔隙率恒定，则单元越厚意味着流体含量越高。考虑到流体减少了基础摩擦，并且假设特定界面处的可用流体与沉积物中的总流体含量成正比，单元的厚度变化将导致沿弧线的板块边界处不同程度的耦合。这可能为边缘板间地震发生的区域差异提供一种解释。此外，我们试图引起人们对通道状沉积物作为剪切应力释放器的可能性的关注。
[1] At the Japan Trench convergent margin, many large interplate earthquakes of greater than M7.5 frequently occur. Their epicenters have uneven distribution, mostly located in the northern area. To investigate the relationship between this distribution and tectonic structures, we have conducted multichannel seismic surveys since 1996. Our data show two kinds of interplate sedimentary units: a wedge-shaped unit and a channel-like unit. Both units have a lower P wave velocity than the basal part of the overriding island arc crust. The wedge-shaped unit having a velocity of 2–3 km/s is widely distributed over the forearc region in the northern area. Its thickness decreases with depth, becoming several hundred meters at a depth of ∼12 km. The channel-like unit having a velocity of 3–4 km/s is observed in the southern area, extending in the downdip direction. Its thickness reaches ∼2 km at a depth of ∼12 km. If the low velocity of these units results from the existence of fluid, as many authors assume, the units being thick implies higher fluid content assuming constant porosity. Considering that fluid reduces basal friction and with an assumption that fluid available at a specific interface is proportional to the total fluid content in the sediment, the thickness variation of the units would cause different degrees of coupling at the plate boundary along the arc. This may provide one explanation for the regional disparity in the interplate earthquake occurrence in the margin. Furthermore, we attempt to call attention to the possibility that the channel-like sediment works as a shear stress releaser.