EAR-PF: What is the role of metasomatic alteration in subduction zone episodic tremor and slip?

该奖项的全部或部分资金来自《2021年美国救援计划法案》(公法117-2)。威廉·胡佛博士被授予NSF EAR博士后奖学金，与导师凯利·康迪特博士一起在华盛顿大学开展研究和教育计划。胡佛博士将研究水-岩石反应在产生神秘的地震现象中所起的作用，这种现象被称为幕式震动和滑动(ETS)，可以在大地震之前发生，特别是沿着俯冲带断层。这项研究将集中于从现代俯冲带(例如华盛顿州和俄勒冈州的卡斯卡迪亚)的ETS特征的深处挖掘出的卡塔利纳岛(南加州)的岩石。宏观和微观尺度的构造和地球化学综合分析将揭示流体作用下的岩石蚀变如何产生具有ETS特征的变形行为。这项工作将提供对ETS源区岩石的重要直接观测，并为现代俯冲带监测和地震研究提供信息。在卡特琳娜岛的实地考察期间，胡佛博士将为来自西语裔服务机构加州州立海峡群岛的学生讲授实地课程，并指导Capstone研究项目。他还将开发和展示教育活动，作为华盛顿大学K-12推广计划的一部分。最后，这项研究将在加布里埃利诺-汤瓦部落的土地上进行，他将通过为该部落举办的外联活动来回报这项研究的实际好处。ETS的流变学模型表明，它可能赋存于交代滑石和绿泥石片岩中，胡佛博士将使用挖掘出的岩石记录来验证这一假设。他将通过Catalina Schist(CA)的野外测绘，确定从ETS源区的地球物理研究中推断出的构造和富含流体条件的地质等价物。他将把露头规模的变形分配与交代变化与主体、常量和微量元素以及锶和锂同位素地球化学联系起来。利用电子束技术的空间分辨微尺度化学和结构分析，他将确定变形机制，并将它们与所有尺度上的成分变化联系起来。这些观测将被置于地震周期的时间背景下，通过散体锂和晶体内扩散计时法。使用这种多尺度的方法，胡佛博士将记录交代作用如何控制现代俯冲带中ETS条件下的变形、分割和机制。这些结果将为未来俯冲带地震的地球物理、理论和实验研究提供信息。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2). Dr. William Hoover has been awarded an NSF EAR postdoctoral fellowship to carry out research and educational plans at the University of Washington alongside mentor Dr. Cailey Condit. Dr. Hoover will investigate the role of water-rock reaction in producing the enigmatic seismic phenomena known as episodic tremor and slip (ETS) that can precede large, damaging earthquakes, particularly along subduction zone faults. This study will focus on rocks from Catalina Island (Southern California) exhumed from depths characteristic of ETS in modern subduction zones (e.g., Cascadia in Washington and Oregon). Integrated macro- and micro-scale structural and geochemical analysis will reveal how rock alteration by fluid flow yields deformation behavior characteristic of ETS. This work will provide important direct observations of rocks from ETS source regions and inform modern subduction zone monitoring and seismic research. During field work on Catalina Island, Dr. Hoover will teach a field course to students from Hispanic-serving institution Cal State Channel Islands and mentor capstone research projects. He will also develop and present educational activities as part of the University of Washington Rockin’ Out K-12 outreach program. Lastly, this research will be carried out on land of the Gabrielino-Tongva Tribe and he will return tangible benefits of the research through outreach events held for the tribe. Rheological modeling of ETS suggests that it may be hosted within metasomatic talc and chlorite schists, and Dr. Hoover will test this hypothesis using the exhumed rock record. He will identify geologic equivalents of the structures and fluid-rich conditions inferred from geophysical studies of ETS source regions through field mapping of the Catalina Schist (CA). He will connect outcrop-scale deformation partitioning to metasomatic changes with bulk major and trace element and Sr and Li isotope geochemistry. Using spatially-resolved micro-scale chemical and structural analysis with electron microbeam techniques, he will determine deformation mechanisms and connect them to compositional changes across all scales. These observations will be placed in the temporal context of the seismic cycle through bulk Li and intra-crystalline diffusion chronometry. Using this multi-scale approach Dr. Hoover will document how metasomatism controls deformation partitioning and mechanisms at the conditions of ETS in modern subduction zones. These results will inform future geophysical, theoretical and experimental studies of subduction zone seismicity.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.