What controls interplate coupling?: Evidence for abrupt change in coupling across a border between two overlying plates in the NE Japan subduction zone
What controls interplate coupling?: Evidence for abrupt change in coupling across a border between two overlying plates in the NE Japan subduction zone
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DOI：
10.1016/j.epsl.2009.04.003
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发表时间：
2009-06
影响因子：
5.3
通讯作者：
N. Uchida;J. Nakajima;A. Hasegawa;T. Matsuzawa
中科院分区：
文献类型：
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作者：
N. Uchida;J. Nakajima;A. Hasegawa;T. Matsuzawa
利用大量重复小地震资料，对日本东北部俯冲带最南端（日本关东以东）的板块间耦合进行了详细研究。在这个海沟-海沟-海沟型三联结区域，俯冲的太平洋板块与两个不同的上覆板块（北美板块和菲律宾海板块）接触。根据包括小型重复地震在内的许多板块间事件的滑动矢量，沿太平洋板块上表面确定了从三重交界处向西北延伸的两个上覆板块之间的边界。根据1993 - 2007年小地震的累积滑动估计的板间耦合系数显示，从南（约0.3）到北（约0.7）跨越边界有明显的变化。这一边界也对应了近80年来沿日本海沟发生的70年代中期板块间地震震源区域的南缘，再次表明了向北耦合更强。我们还利用从全国地震仪台网获得的大量走时数据研究了沿板块边界的震源分布和地震速度结构。结果表明，在菲律宾海板块覆盖区域，太平洋板块上方有明显的低速带，沿板块边界地震活动性低；而在北美板块覆盖区域，没有低速带，地震活动性高。这些观测结果表明，上覆板块的地质差异控制着板块界面的大规模耦合。
Interplate coupling in the southernmost extent of the northeast Japan subduction zone (east off-Kanto, Japan) is investigated in detail using a large data set of small repeating earthquakes. In this region of the trench-trench-trench type triple junction, the subducting Pacific plate is in contact with two different overlying plates (the North American and Philippine Sea plates). The border between the two overlying plates extending northwestward from the triple junction is identified along the upper surface of the Pacific plate based on the slip vectors of many interplate events including small repeating earthquakes. The interplate coupling coefficient estimated from the cumulative slip of small repeating earthquakes for the period from 1993 to 2007 reveals a distinct change from south (ca. 0.3) to north (ca. 0.7) across the border. This border also corresponds to the southern limit of the source areas of M> 7 interplate earthquakes in the last 80 years along the Japan trench, again indicating the stronger coupling to the north. We also investigate hypocenter distribution and seismic velocity structure along the plate boundary from a large number of travel-time data obtained from the nationwide seismograph network. The results reveal a distinct low-velocity zone just above the Pacific plate and low seismicity along the plate boundary in the region overlain by the Philippine Sea plate, whereas there are no low-velocity zones and the seismicity is high in the region overlain by the North American plate. These observations imply that the geological difference of overlying plate controls large-scale coupling at the plate interface.