Collaborative Research: the role of fluids in intermediate-depth seismicity and wedge anisotropy: Case studies for Cascadia and Alaska, with a comparison to Japan

这项研究的主要目标是确定地幔中流体的存在是否是一个控制因素，决定地震发生在俯冲带内的位置，特别是沿着断层，使下行的构造板块向周围的粘性地幔更深地滑动。这种地震活动位于“冷”俯冲带（如阿拉斯加和东北）的地壳内，而位于“暖”俯冲带（如卡斯卡迪亚和南开）的地幔内，这一事实表明，流体在其中起着重要作用。将评估地震波传播速度的方向依赖性，以便考虑地震位置的可能偏差。同时，还可获得黏性流动地幔内部的变形信息。横波速度和纵波速度的比值将提示流体存在或不存在的地方。这些约束条件将指导俯冲带地幔流动和温度的计算机模拟。这些结果将与与板块脱水相关的矿物相变化的岩石学模型联系起来，该模型在板块界面附近引入流体并导致弧火山作用的产生。三位地球科学家——地球动力学家、岩石学家和地震学家——的深入合作，成为跨学科地球系统研究的典范。研究生和本科生将接受在其子学科中使用最先进方法的培训，并学习如何解决与互补子学科不断发展的结果之间的相互作用。与日本科学家的国际合作提供了最好的仪器和充分研究日本俯冲系统的途径。这项研究利用了美国国家科学基金会在卡斯卡迪亚的地质系统和地球观测项目正在进行的工作，并计划在阿拉斯加进行。

The main goal of this study is to determine whether the presence of fluids within Earth's mantle is a controlling factor determining where earthquakes occur within subduction zones, specifically along the fault that enables the down-going tectonic plate to slip deeper into surrounding viscous mantle. The fact that this seismicity is located within the crust at 'cool' subduction zones, such as Alaska and Tohoku, versus in the mantle at 'warm' subduction zones, such as Cascadia and Nankai, suggests that fluids play an important role. Directional dependence of seismic wave propagation speeds will be assessed, so that possible bias in earthquake locations can be accounted for. Simultaneously, information about deformation within the viscously flowing mantle will be obtained. Ratios of shear and compressional wave velocities will suggest where fluids are present or not. These constraints will guide computer modeling of mantle flow and temperature in the subduction zones. These results will be linked to petrologic models of mineral phase change associated with plate dehydration that introduce fluids near the plate interface and lead to the generation of arc volcanism.In-depth collaboration by three geoscientists- a geodynamist, petrologist, and seismologist, serves as a model of interdisciplinary Earth System research. Graduate and undergraduate students will receive training in the use of state-of-the-art methods in their sub-discipline as well as learning how to address interplay with evolving results from complementary sub disciplines. The international collaboration with Japanese scientists provides access to the best instrumented and well-studied Japanese subduction system. The study leverages ongoing work in the NSF GeoPRISMS and EarthScope Programs at Cascadia and that planned for Alaska.