Deep seismic structure of the seismogenic plate boundary in the off-Sanriku region, northeastern Japan
Deep seismic structure of the seismogenic plate boundary in the off-Sanriku region, northeastern Japan
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日本东北三陆地区发震板块边界的深部地震结构
DOI：
10.1016/s0040-1951(99)00298-x
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发表时间：
2000
期刊：
影响因子：
2.9
通讯作者：
A. Hasegawa
中科院分区：
文献类型：
--
作者：
S. Ito;R. Hino;S. Matsumoto;H. Shiobara;H. Shimamura;T. Kanazawa;Takeshi Sato;J. Kasahara;A. Hasegawa
确定了日本海沟内斜坡区北部三陆外海的孕震板块边界带的深部地震构造。由海底地震仪和当地陆地地震台网记录的1994年远方三陆7.5级地震的余震走时数据使我们能够成像该地区的三维地震速度结构。沿板块边界，俯冲太平洋板块的最顶层是厚度为10公里的P波低速层，其厚度约为7 Kms−。目前的分析表明，这一层被解释为俯冲洋壳，至少向下延伸到约40公里处，没有任何速度变化。在盖层板块中，我们发现在东经142.5°的日本东北弧太平洋海岸线之间有一个相当高的P波速度带，约8 Kms−1，这表明地幔楔形的槽状脚趾的速度明显高于弧陆区之下的速度。高P波速度趾部向陆地的界限与孕震板块边界的向下界限相对应。再往东，P波速度约为6 Kms−1。所获得的构造图像表明，沿板块边界上覆覆板块的性质明显不同。在孕震带东半部，岛弧地壳与俯冲洋壳相互接触，而高速地幔楔则构成孕震带深部的上盘。
We determined the deep seismic structure of the seismogenic plate boundary zone of off-Sanriku, the northern part of the Japan Trench inner slope area. Travel time data from aftershocks of the 1994 Far-off Sanriku earthquake (M=7.5) recorded both by ocean bottom seismographs and the local land seismic network enable us to image the three-dimensional seismic velocity structure of the region. Along the plate boundary, there exists a P-wave low-velocity layer of ca. 7kms−1and with thickness <10km as the topmost layer of the subducting Pacific plate. The present analysis indicates that this layer, interpreted as the subducting oceanic crust, continues without any velocity variations at least down to ca. 40km depth. In the overriding plate, we found a zone of considerable high P-wave velocity, ca. 8kms−1, between the Pacific coastal line of the northeastern Japan arc at the longitude of 142.5°E. This manifests that the trenchward toe of the mantle wedge has significantly higher velocity than that beneath the land area of the arc. The landward limit of the high P-wave velocity toe corresponds to the down-dip limit of the seismogenic plate boundary. Further to the east, the P-wave velocity is ca 6kms−1. The structure image obtained indicates that the nature of the overriding plate is significantly different along the plate boundary. In the eastern half of the seismogenic zone, the island arc crust and subducting oceanic crust are in contact with each other, whereas the high velocity mantle wedge makes up the hanging wall of the deeper part of the seismogenic zone.