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

这项急切的提议将从普吉特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巨型逆冲带。其想法是，深区域断层充当向上迁移流体的通道，这些流体是沿着北美和进入的胡安德富卡板块之间的板块界面加热产生的。如果Puget Sound热柱具有俯冲带源，则可能提供一种监测板块间流体压力和化学的手段，并为研究卡斯卡迪亚俯冲带巨型逆冲断裂的滑动提供新的途径。该项目是开发预测模型以了解人口稠密的太平洋西北部地震灾害的第一步。在与普吉特湾地区非常相似的环境中，已经观察到流体和天然气通过活动俯冲带断层上覆的弧前地壳向上迁移，包括基伊半岛的日本海沟、新西兰希库兰吉边缘的新西兰海沟和墨西哥的下加利福尼亚半岛。尽管这些流体渗漏释放出具有氦、氧、氢同位素特征的流体，这些特征明确地表明它们来自俯冲带断层，但它们都没有释放出具有普吉特湾内观察到的活力或广泛空间分布的流体和气体。关键的是，以前全球识别的弧前热柱都不在俯冲带，在那里周期性地发生幕式地震和滑动(ETS)事件-这些事件是由俯冲带断层上周期性的局部滑动引起的。在卡斯卡迪亚，这些ETS事件的准周期为14个月，振幅和间隔的变化被新确认为区域断裂和大型幕式巨型逆冲地震的潜在前兆。如果新的普吉特羽流被发现来自俯冲带巨型逆冲带，这将是利用排放变化和ETS行为之间的相关性来了解巨型逆冲上的滑移的第一步。这一裁决反映了NSF的法定使命，并通过使用基金会的智力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.