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

这项EAGER提案将从普吉湾新发现的气体和流体羽流中获取样本，以确定羽流是否来自卡斯卡迪亚俯冲带巨型逆冲断层。这个想法是，深部区域断层作为向上迁移的流体的通道，这些流体是通过沿着北美和即将到来的胡安德富卡板块之间的板块界面加热而产生的。如果普吉特湾的羽流有一个俯冲带的来源，羽流可能提供一种手段来监测压力和板块之间的流体化学，并提供一种新的方法来研究卡斯卡迪亚俯冲带巨型逆冲断层的滑动。该项目是为理解人口稠密的太平洋西北部地区的地震灾害而开发预测模型的第一步。在与普吉湾地区非常相似的环境中，包括新西兰希库朗吉边缘的纪伊半岛上的日本海沟和墨西哥下加利福尼亚半岛上的日本海沟，观察到了流体和气体通过覆盖在活动俯冲带断层上的弧前地壳向上迁移。尽管这些流体渗漏释放出具有氦、氧、氢同位素特征的流体，这些特征明确地将它们识别为来自俯冲带断层，但它们都没有释放出具有在普吉特海湾内观察到的活力或广泛空间分布的流体和气体。重要的是，以前全球确定的弧前羽流都没有出现在俯冲带中，那里会发生周期性的幕式震颤和滑动（ETS）事件-这是由俯冲带断层上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，振幅和间隔的变化是新认识到的潜在前兆，区域断层和大型幕式巨型逆冲断层地震。如果发现新的普吉特羽流来自俯冲带大推力区，这将是使用排放变化和ETS行为之间的相关性来理解大推力滑动的第一步。该奖项反映了NSF的法定使命，并被认为值得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来支持。

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.