Thermal regime and petrologic metamorphism in Alaska: Implications for subduction interface and wedge earthquakes

Characterized by repeated large earthquakes, slow slips, and tectonic tremors with their simultaneous release of large amounts of energy, the unstable subduction interface beneath Alaska presents a chance to understand the composite dynamic transition from deep to shallow subduction channel where these enigmatic fault slips and seismic events occur. The complex subducted slab morphology associated with the frequent occurrence of various types of faulting behaviors in Alaska is poorly understood. Our result shows that the subduction of the Pacific plate and the subsequent release of large amounts of fluid likely contribute to the repeated fast and slow earthquakes there, as evidenced by the petrological metamorphic transition in the incoming plate. The offshore Alaska seismogenic zone, as well as the slow earthquakes identified near the Upper Cook Inlet, compare well with the distribution of slab dehydration slivers, including large destructive earthquakes that have occurred in Alaska. The fluid upwelling from dewatered oceanic crust and the continental wedge serpentinizing is probably related to various transportation pathways controlled by dip angle and upwell in the predominant direction following the subduction channel or veins in the overriding lithosphere.

阿拉斯加下方的不稳定俯冲界面，以频发的大地震、慢滑事件与构造震颤及其伴随的大规模能量释放为典型特征，为我们探究该区域神秘断层滑动与地震事件发生的深-浅俯冲通道（subduction channel）复合动力转变过程提供了重要契机。阿拉斯加地区频繁出现多种类型的断层活动，与之相关的复杂俯冲板片形态目前尚未得到充分认知。我们的研究结果表明，太平洋板块俯冲及其后续伴随的大规模流体释放，可能是该区域反复发生快慢地震的关键诱因，这一结论可由俯冲入射板块（incoming plate）的岩石学变质转变得到佐证。阿拉斯加近海发震带，以及库克湾上游附近发现的慢地震事件，其分布特征与板片脱水条带（slab dehydration slivers）的分布高度吻合，这也涵盖了阿拉斯加地区曾发生的各类大型破坏性地震。从脱水洋壳及大陆楔蛇纹岩化过程中析出的上升流体，或与受倾角调控、且主要沿俯冲通道（subduction channel）或上覆岩石圈（overriding lithosphere）中的岩脉方向上涌的各类运移路径密切相关。