Seismic evidence for water transportation in the forearc off Northern Japan
Seismic evidence for water transportation in the forearc off Northern Japan
复制标题
日本北部弧前水运的地震证据
DOI：
10.1029/2019jb018600
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发表时间：
2020
期刊：
影响因子：
--
通讯作者：
Dapeng Zhao
中科院分区：
文献类型：
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作者：
Zhiteng Yu;Dapeng Zhao
水循环在弧火山作用、地震孕育、地幔流变学和俯冲带热结构中起着重要作用。以往的地震研究表明，在日本东北部和北海道的巨型逆冲断层带中存在强烈的结构不均匀性。然而，由于缺乏长期的海底地震观测站，对弧前地区的水运仍然知之甚少。利用日本北方太平洋永久海底地震台网（S‐net）最近记录的高质量数据，研究了千岛群岛和东北地区弧前区地壳和上地幔的精细三维P波速度（Vp）结构。我们的研究结果显示，地幔楔角部的速度很高，这意味着那里的蛇纹化程度很低。我们认为，研究区的弧前地幔是寒冷和无水的。弧前区下的板片界面可能具有低渗透性，这控制了流体向地幔楔和上覆板块的通量。俯冲太平洋板块顶部的低Vplayer被解释为俯冲洋壳。俯冲洋壳的脱水作用发生在80-120公里深处，为上覆地幔楔提供了大量的水，产生弧火山，部分水可能向上迁移到浅水区。大型逆冲断层地震（Mw≥ 6.0）主要发生在逆冲断层带的低Vp斑块周围。低渗透性板块界面的破坏将导致流体向上流动，这可能引发大型逆冲断层地震和弧前地幔楔中的地震活动。
The water cycle plays an essential role in arc volcanism, earthquake generation, mantle rheology, and thermal structure of subduction zones. Previous seismic studies have revealed strong structural heterogeneities in the megathrust zone in Northeast Japan and Hokkaido. However, water transportation in the forearc region remains poorly understood due to the lack of long‐term seismic observatories at the seafloor. Using high‐quality data recently recorded by the permanent ocean‐bottom‐seismometer network (S‐net) in the Pacific Ocean off Northern Japan, we study the fine three‐dimensionalPwave velocity (Vp) structure of the crust and upper mantle beneath the Kuril and Tohoku forearc region. Our results reveal high velocities in the mantle‐wedge corner, implying a low degree of serpentinization there. We suggest that the forearc mantle in the study region is cold and anhydrous. The slab interface under the forearc area may have a low permeability, which controls the fluid flux to the mantle wedge and the overriding plate. A low‐Vplayer atop the subducting Pacific plate is interpreted as the subducted oceanic crust. Dehydration of the subducted oceanic crust occurs at depths of 80–120 km, providing a large volume of water to the overriding mantle wedge to produce arc volcanoes, and part of the water may migrate upward to the shallow area. Large megathrust earthquakes (Mw≥ 6.0) mainly occurred around low‐Vppatches in the megathrust zone. Destruction of the low‐permeability slab interface would result in fluid flow upward, which may trigger large megathrust earthquakes and seismicity in the mantle wedge under the forearc.