EAGER: Bubble Plume Emissions from Fault Zones within the Puget Sound Forearc

这项EAGER提案将从普吉特海湾新发现的气体和流体羽流中获取样本，以确定这些羽流是否来自卡斯卡迪亚俯冲带的大逆冲构造。该理论认为，深层区域断层充当了流体向上运移的通道，这些流体是由北美板块和即将到来的胡安·德·富卡板块之间的板块界面加热产生的。如果普吉特湾的地幔柱来源于俯冲带，那么该地幔柱将为监测板块间流体的压力和化学性质提供一种手段，并为研究卡斯卡迪亚俯冲带逆冲断层的滑动提供一种新的方法。该项目是开发预测模型以了解人口稠密的太平洋西北地区地震危害的第一步。在与普吉特海湾地区非常相似的环境中，包括Kii半岛的日本海沟、新西兰的Hikurangi边缘和墨西哥的下加利福尼亚半岛，已经观察到流体和天然气通过覆盖在活动俯冲带断层上的弧前地壳的向上运移。尽管这些流体渗漏所释放的流体具有氦、氧、氢同位素特征，可以明确地识别它们来自俯冲带断层，但它们所释放的流体和气体都没有在普吉特海湾观察到的那么活跃或广泛的空间分布。至关重要的是，以前全球确定的前弧羽流都没有位于发生周期性幕式震颤和滑动（ETS）事件的俯冲带，这些事件是由俯冲带断层的周期性局部滑动引起的。在卡斯卡迪亚，这些ETS事件的准周期为14个月，其振幅和间隔的变化被新认识为区域断裂和大型幕式大逆冲地震的潜在前兆。如果发现新的普吉特羽流来自俯冲带的大逆冲带，这将是利用排放变化与ETS行为之间的相关性来理解大逆冲滑动的第一步。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This EAGER proposal will obtain samples from newly identified gas and fluid plumes in Puget Sound to determine whether the plumes come from the Cascadia subduction zone megathrust. The idea is that deep regional faults act as pathways for upward migration of fluid that has been generated by heating along the plate interface between the North America and the incoming Juan de Fuca Plate. If the Puget Sound plumes have a subduction zone source, the plumes may provide a means to monitor the pressure and chemistry of the fluid between the plates, and provide a new approach for studying slip on the Cascadia subduction zone megathrust fault. This project is a first step toward developing predictive models for understanding seismic hazards in the heavily-populated Pacific Northwest.Upward migration of fluid and gas through the forearc crust that overlies active subduction zone faults has been observed in settings very similar to the Puget Sound region, including Japan Trench on the Kii peninsula, New Zealand at the Hikurangi margin, and on the Baja California Peninsula, Mexico. Although these fluid seeps emit fluid with helium, oxygen, hydrogen isotope signatures that unambiguously identify them as coming from the subduction zone fault, none of them emit fluid and gas with the vigor or wide spatial distribution observed within Puget Sound. Critically, none of the previous globally-identified forearc plumes are in subduction zones where periodic Episodic Tremor and Slip (ETS) events occur - that arise from periodic local slippage on the subduction zone fault. At Cascadia, these ETS events have a quasi-period of 14 months and variations in the amplitude and intervals are newly-recognized as potential precursors to both regional faulting and large episodic megathrust earthquakes. If the the new Puget plumes are found to be derived from the subduction zone megathrust zone, it would be the first step in using correlations between the variations in emissions and ETS behavior to understand slip on the megathrust.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.