Collaborative Research: A Geochemical Approach to Quantifying the Magnitude of Strain and Fluid Flow along the Subduction Interface

地球上最大的地震发生在沿着巨型逆冲断层（俯冲板块界面），这些断层将俯冲带中的刚性构造板块分开。弹性应变沿着这些板块界面的积累和释放取决于大地震后界面的“愈合”。该项目将描述在地震之间控制这种愈合的化学和机械过程。对现在暴露在陆地上的古代俯冲界面的观测将用于为滑动和流体流动的数值模型提供信息。总之，这些方法将使研究人员能够确定俯冲带过程如何影响地震的空间和时间模式，这是评估与活跃俯冲带相关的危害的重要一步。这项研究包括支持一名早期职业教师，一名博士。学生和9名本科生。其中六名本科生将从化身世界大学招募，这是一个为当地西班牙裔社区服务的本科生机构。该项目包括对两个挖掘出的地形进行结构和地球化学调查，这些地形保存了与全球活跃俯冲带阵列的板块界面有关的物理和化学条件的记录。日本的Shimanto带和阿拉斯加的Kodiak增生复合体结合在一起，形成了一个复合记录，深度从8到20公里，峰值温度在150到350摄氏度之间。在几次实地活动中收集的样品的基于电子显微镜的元素绘图将能够量化矿物相及其随渐进应变的再分布。结合阴极发光成像，电子背散射衍射，流体包裹体显微测温将约束古温度和有限应变，并确定变形机制。应变率的定量估计将通过应变幅值与剪切带厚度的现场观测和现今板块收敛速率的估计相结合来得出。这些测量和观测结果将被用来提供一个数值模型，该模型将地震滑动、流体流动和地震间再强化对板块界面地震时空分布的影响参数化。多学科工作计划旨在解决以下基本问题：Q1）与地震间变形相关的体应变和剪应变的幅度是多少？Q2）在块体中，矿物沿着鳞片状组构的溶解和在裂缝中的沉淀之间是否存在平衡？问题3）二氧化硅的局部扩散质量转移与外部衍生流体溶解二氧化硅的流入对石英脉形成的相对贡献是什么？从孕震区的上倾端到下倾端，变形机制的划分有何不同？该奖项反映了NSF的法定使命，并被认为是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的支持。

Earth’s largest earthquakes occur along the megathrusts (the subduction plate interfaces) that separate rigid tectonic plates in subduction zones. The accumulation and release of elastic strain along these plate interfaces is predicated on the “healing” of the interface after the large earthquakes. This project will characterize the chemical and mechanical processes that control this healing during the time between earthquakes. Observations of ancient subduction interfaces, now exposed on land, will be used to inform a numerical model for slip and fluid flow. Together, these approaches will allow the investigators to determine how subduction zone processes impact the spatial and temporal patterns of earthquakes—an important step in assessing the hazards associated with active subduction zones. The study includes support for an early-career faculty member, a Ph.D. student, and nine undergraduates. Six of the undergraduates will be recruited from University of the Incarnate Word, an undergraduate body that serves a local Hispanic community.This project comprises a structural and geochemical investigation of two exhumed terrains that preserve a record of the physical and chemical conditions relevant to the plate interface of the global array of active subduction zones. Combined, the Shimanto belt in Japan and the Kodiak Accretionary complex in Alaska, form a composite record spanning depths from 8 to 20 km and peak temperatures between 150 and 350˚C. Electron-microscope-based elemental mapping of samples collected during several field campaigns will enable quantification of mineral phases and their redistribution with progressive strain. Combined cathodoluminescence mapping, electron backscatter diffraction, and fluid-inclusion microthermometry will constrain paleotemperatures and finite strain, and identify deformation mechanisms. Quantitative estimates of strain rate will be derived by combining strain magnitudes with field observations of shear zone thickness and present-day estimates of plate convergence rate. These measurements and observations will be used to inform a numerical model that parameterizes the effects of seismic slip, fluid flow and interseismic restrengthening on the temporal and spatial distribution of earthquakes on the plate interface. The multidisciplinary workplan is designed to address the following fundamental questions: Q1) What are the magnitudes of volume strain and shear strain associated with interseismic deformation? Q2) Is there a balance between dissolution along the scaly fabric and precipitation of minerals within cracks in blocks? Q3) What are the relative contributions to quartz vein formation of local diffusive mass transfer of silica versus the influx of dissolved silica by an externally derived fluid? Q4) How does partitioning of deformation mechanisms vary from the updip to the downdip ends of the seismogenic zone?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.