Collaborative Research: Earthscope integrated investigation of Cascadia subduction zone tremor, structure and process

0545441克里格在这个项目中，在卡斯卡迪亚俯冲带进行了综合野外实验，以阐明水的运输，地壳滑动，幕式震颤和弧岩浆活动之间的关系。最终目标是利用地震学、大地测量学和岩石学的工具探索俯冲带中的H2O过程，并将这些结果与地球动力学和地球化学的互补约束相结合。地震成像是用来照亮（i）下降的海洋板块，它变质，和（ii）地幔楔，流体可能会产生含水相，如蛇纹岩，或在火山弧下，原生岩浆。该实验旨在穿越地震延伸到近100公里深度的卡斯卡迪亚系统的一部分，从而可以调查流体释放与Wadati-Benioff区地震发生之间的关系。流体的输送也可能是间歇性震颤和滑动（ETS）的主要驱动力，卡斯卡迪亚观察到的这种现象可能比地球上其他任何地方都要好，包括本实验中的源区。从已知的震源区的震颤的测量集成与来自GPS数据和现有的长基线倾斜仪的滑动分布。与地震成像一起，这些观测产生了无与伦比的数据集，用于确定地震、滑动与成像显示下行板块变质或上覆地幔楔水合作用的区域之间的关系。基本实验有四个组成部分：一个由灵活阵列仪器组成的宽带成像阵列，与大脚怪相结合，三个靠近非火山震颤源的小孔径地震阵列，分析PBO和PANGA GPS数据集，以确定幕式滑动事件的细节，并进行综合建模。宽带阵列的特点是在卡斯卡迪亚俯冲系统的一部分，其中包括中深度地震和Nisqually地震震源，在一个交错的配置，允许沿罢工的影响进行测试的密集横断面。这是由两个交叉线补充，一个交叉的板块，地壳似乎是脱水，和一个在瀑布山麓采样弧的根源。地震和GPS阵列尽可能与宽带成像并置，以允许同时定位地震和滑动并成像其震源区域。对这些数据进行了适合于这些数据的各种分析，包括对震颤波的波前方向进行阵列分析、地震散射波的迁移、Vp、Vs和Q的层析成像、剪切波分裂、地震重定位、调查与板块相互作用的高频相位以及为检测和量化瞬态事件而设计的专门全球定位系统处理。结合卡斯卡迪亚俯冲系统的详细岩石学-热模型对结果进行了解释。这些结果被用来放置在下行板块内的脱水途径，在中间深度的结构和地震活动之间的关系，瞬态应变事件和结构之间的关系，温度，熔融和挥发物含量的地幔楔，和大陆地壳的增长新的约束。

0545441CreagerIn this project, an integrated field experiment is undertaken in the Cascadia subduction zone to elucidate the relationship between water transport, aseismic slip, episodic tremor, and arc magmatism. The ultimate goal is to explore H2O processes in subduction zones using the tools of seismology, geodesy and petrology, and to integrate these results with complementary constraints from geodynamics and geochemistry. Seismic imaging is employed to illuminate (i) the descending oceanic plate where it metamorphoses, and (ii) the mantle wedge where fluids may be producing hydrous phases such as serpentine or, beneath the volcanic arc, primary magmas. The experiment is designed to traverse the one part of the Cascadia system where earthquakes extend to nearly 100 km depth, thus permitting an investigation of the relationship between the release of fluids and the generation of Wadati-Benioff-zone earthquakes. The transport of fluids may be also a primary driver for episodic tremor and slip (ETS), a phenomenon observed in Cascadia perhaps better than anywhere else on the planet, including source regions within this experiment. Measurements of tremor from known source regions are integrated with slip distributions derived from GPS data and existing long-baseline tiltmeters. Together with the seismic imaging, these observations yield an unparalleled data set for determining the relationship between tremor, slip and the regions where imaging indicates metamorphism of the down-going plate or hydration of the overlying mantle wedge.The basic experiment has four components: a broadband imaging array of flexible-array instruments integrated with Bigfoot, three small-aperture seismic arrays near sources of non-volcanic tremor, analysis of the PBO and PANGA GPS data sets to define the details of episodic slip events, and integrative modeling. The broadband array features a dense transect across the part of the Cascadia subduction system that includes intermediate-depth earthquakes and the Nisqually earthquake hypocenter, in a staggered configuration to allow along-strike effects to be tested. This is complemented by 2 cross lines, one crossing the slab where the crust appears to be dehydrating, and one in the Cascades foothills to sample the roots of the arc. The tremor and GPS arrays are collocated with the broadband imaging as much as possible, to allow simultaneous location of tremor and slip and imaging of their source region. These data are subject to the gamut of analyses appropriate to such data, including array analysis for wave-front orientation of tremor waves, migration of teleseismic scattered waves, tomographic images of Vp, Vs and Q, shear-wave splitting, earthquake relocation, investigation of high-frequency phases interacting with the slab, and specialized GPS processing designed for the detection and quantification of transient events. The results are interpreted in conjunction with detailed petrological-thermal models of the Cascadia subduction system. These results are used to place new constraints on the dehydration pathways within the down-going plate, the relationship between structure and seismicity at intermediate depths, the relationship between transient strain events and structure, the temperature, melt and volatile content of the mantle wedge, and the growth of continental crust.