期刊
NATURE GEOSCIENCE
卷 1, 期 11, 页码 771-776出版社
NATURE PUBLISHING GROUP
DOI: 10.1038/ngeo318
关键词
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资金
- Swiss Re
The Philippine Sea and Pacific plate slabs both subduct beneath Tokyo, and so their configuration and seismic potential have been subject to intensive study(1-8). Previous work suggests that the Philippine Sea slab extends up to 100 km northwest of Tokyo and subducts to a depth of 90 km beneath the Kanto basin, where it is folded against the underlying Pacific slab. Here we evaluate seismic data in three dimensions and delineate a distinct 25-km-thick and 100-km-wide body beneath the Kanto basin that has hitherto been considered to be part of the Philippine Sea slab. We find that several of its characteristics - such as its high seismic velocity and the presence of a double seismic zone - point instead to an affinity with the Pacific slab, implying that the Philippine Sea slab penetrates to depths of only 35 - 40 km beneath the Kanto basin. We propose that the body is a fragment of Pacific lithosphere that formed by the collision of two intersecting seamount chains with the Japan Trench 2 - 3 million years ago. We suggest that such slab fragments may not be uncommon, especially where seamount subduction deforms trenches and near triple junctions.
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