Subduction of a wedge‐shaped Philippine Sea plate beneath Kanto, central Japan, estimated from converted waves and small repeating earthquakes
Subduction of a wedge‐shaped Philippine Sea plate beneath Kanto, central Japan, estimated from converted waves and small repeating earthquakes
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DOI：
10.1029/2009jb006962
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发表时间：
2010-07
影响因子：
--
通讯作者：
N. Uchida;T. Matsuzawa;J. Nakajima;A. Hasegawa
中科院分区：
文献类型：
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作者：
N. Uchida;T. Matsuzawa;J. Nakajima;A. Hasegawa
[1]为了了解东京都地区的地震构造，我们估计了关东俯冲下的菲律宾海板块(PHS)的构型。除了划定小灵通上边界和下边界的小规模重复地震外，以前未被识别的来自下边界中继源的上边界转换波对边界位置提供了新的限制。794个S到P波和212个P到S转换波与∼200中继站位置的结果表明：(1)小灵通呈楔形，厚度从东京以下50公里处减至东北端为零；(2)关东东部小灵通相对平坦，在其东北端附近向上弯曲。根据伊豆-博宁弧前的PHS也具有类似的楔形形状，我们推测它的形状是在其俯冲之前形成的。另一方面，位于其东北端的相对平坦的PHS及其向上弯曲可能是与下伏的厚太平洋板块(PAC)相互作用而持续变形的结果。PHS俯冲前的弧前历史和俯冲后与PAC接触的历史表明，这部分PHS的温度比其他地区低，这可能是关东PHS异常深震活动的原因。较低的PHS温度意味着大地震的震源区可能比预期延伸得更深，这是评估东京灾难性地震地点时的一个重要事实。
[1] We estimate the configuration of the Philippine Sea plate (PHS) subducted beneath Kanto to understand the seismotectonics in the Tokyo metropolitan area. In addition to small repeating earthquakes that delineate both the upper and lower boundaries of the PHS, previously unrecognized converted waves at its upper boundary from lower-boundary repeater sources provide a new constraint on the position of the boundary. The results from 794 S-to-P and 212 P-to-S converted waves together with ∼200 repeater locations show that (1) the PHS has a wedge-like shape, decreasing in thickness from 50 km beneath Tokyo to zero at its northeastern limit, and (2) the PHS is relatively flat in the eastern part of Kanto and bends upward near its northeastern limit. From the fact that the PHS in the Izu-Bonin forearc also has a similar wedge-like shape, we infer that its shape was formed before its subduction. On the other hand, the relatively flat PHS at its northeastern limit and its upward bend are probably a consequence of ongoing deformation from an interaction with the underlying thick Pacific plate (PAC). The history of the PHS as a forearc before subduction and its contact with the PAC after subduction suggests that the temperature of this part of the PHS is colder than other regions, which probably causes anomalously deep seismicity on the PHS in Kanto. Colder PHS temperatures imply that the source regions of large earthquakes may extend deeper than expected, an important fact when assessing the locations of disastrous earthquakes for Tokyo.