Spatial variations of incoming sediments at the northeastern Japan arc and their implications for megathrust earthquakes
Spatial variations of incoming sediments at the northeastern Japan arc and their implications for megathrust earthquakes
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DOI：
10.1130/g46757.1
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发表时间：
2020-06-01
期刊：
影响因子：
5.8
通讯作者：
Miura, Seiichi
中科院分区：
文献类型：
--
作者：
Gou Fujie;Kodaira, Shuichi;Miura, Seiichi
流入沉积物的性质是俯冲带发生大规模逆冲地震的关键控制因素。在2011年M-w 9东北地震（日本近海）中，俯冲洋板块输送的富含蒙脱石的粘土矿物在海沟附近巨大板间同震滑动的发展中发挥了关键作用。最近，我们在太平洋板块西北部进行了密集的可控震源地震调查，以调查传入的海洋板块的性质。我们的地震反射数据表明，在大多数地区，海底与声学基底之间的沉积层厚度为几百米，但也有少数地区的沉积物似乎非常薄。我们的广角地震数据表明，在这些薄沉积物地区的声学基底不是海洋地壳的顶部，而是与最近的火山活动有关的沉积物内的岩浆侵入。这意味着这些地方的沉积物下部，包括富含蒙皂石的远洋红棕色粘土层，已受到严重干扰和热变质。2011年东北地震的巨大同震滑动在一个刚刚开始俯冲的薄沉积物区域附近停止。基于这些观察，我们提出，后扩张的火山活动在俯冲前的海洋板块是一个因素，可以塑造的规模和分布的板间地震俯冲后，通过其干扰和热变质的当地沉积层。
The nature of incoming sediments is a key controlling factor for the occurrence of megathrust earthquakes in subduction zones. In the 2011 M-w 9 Tohoku earthquake (offshore ,Japan), smectite-rich clay minerals transported by the subducting oceanic plate played a critical role in the development of giant interplate coseismic slip near the trench. Recently, we conducted intensive controlled-source seismic surveys at the northwestern part of the Pacific plate to investigate the nature of the incoming oceanic plate. Our seismic reflection data reveal that the thickness of the sediment layer between the seafloor and the acoustic basement is a few hundred meters in most areas, but there are a few areas where the sediments appear to he extremely thin. Our wide-angle seismic data suggest that the acoustic basement in these thin-sediment areas is not the top of the oceanic crust, but instead a magmatic intrusion within the sediments associated with recent volcanic activity. This means that the lower part of the sediments, including the smectite-rich pelagic red-brown clay layer, has been heavily disturbed and thermally metamorphosed in these places. The giant coseismic slip of the 2011 Tohoku earthquake stopped in the vicinity of a thin-sediment area that is just beginning to subduct. Based on these observations, we propose that post-spreading volcanic activity on the oceanic plate prior to subduction is a factor that can shape the size and distribution of interplate earthquakes after subduction through its disturbance and thermal metamorphism of the local sediment layer.