Developing a comprehensive model of subduction and continental accretion at Cascadia

卡斯卡迪亚是了解俯冲动力学和大陆吸积作用的最佳地点，因为它拥有世界上最年轻的俯冲板块之一和广泛的构造单元。卡斯卡迪亚会议上可以解决各种科学问题：是什么控制了俯冲带的分段？水在俯冲带中的运输作用是什么？熔融发生在哪里，岩浆如何在地幔和地壳中迁移？大洋岩石圈是如何与大陆共生的？古地震记录表明，卡斯卡迪亚曾发生过~M9级大地震，因此需要加强对大地震的地震和海啸危害的评估。本项目开发并实施了一种先进的地震学方法，以建立整个卡斯卡迪亚俯冲带地壳和上地幔的全面、高分辨率速度模型。速度模型提供了详细的结构框架和对俯冲过程的新理解。一个解析良好的模型的结构相关性有助于解决弧前地幔的蛇纹岩作用是否沿走向发生实质性变化，以及它与沉积物俯冲、板块上先前存在的特征和火山弧下的熔体产生的关系。该项目测试了幕式地震和慢滑事件的反复发生是否与俯冲板块或俯冲大洋板块的性质有关。新的地壳模型有助于理解大洋岩石圈的吸积对大陆生长和俯冲演化的贡献。准确和高分辨率地描述地壳和上地幔结构对于完善卡斯卡迪亚的地震和海啸危险评估也是至关重要的。

Cascadia is a prime site to understand subduction dynamics and continental accretion, because it has one of the youngest subducting slabs in the world and a wide range of tectonic units. A variety of scientific questions can be addressed at Cascadia: What controls the subduction zone segmentation? What is the role of water transport in the subduction zone? Where does melting occur and how does magma migrate in the mantle and crust? And how does oceanic lithosphere accrete to the continent? Paleoseismic records show that Cascadia has a history of generating ~M9 megathrust earthquakes, so research is needed to improve the assessment of seismic and tsunami hazards from megathrust earthquakes.This project develops and implements an advanced seismological method to construct a comprehensive, high-resolution velocity model of the crust and upper mantle for the entire Cascadia subduction zone. The velocity model provides a detailed structural framework and new understanding of the subduction processes. The structural correlations of a well-resolved model help address whether serpentinization of the forearc mantle varies substantially along strike and how it is related to the subduction of sediments, pre-existing features on the slab, and melt production beneath the volcanic arc. The project tests whether the recurrence of episodic tremor and slow slip events is related to properties of the overriding plate or the subducting oceanic plate. The new crustal model helps in understanding how accretion of oceanic lithosphere contributes to continental growth and subduction evolution. Accurate and high-resolution characterization of the crust and upper mantle structure is also critical to refining seismic and tsunami hazard assessment in Cascadia.