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是否存在的流体在地球的地幔是一个控制因素，确定地震发生在俯冲带内，特别是沿着断层，使下行构造板块滑入周围的粘性地幔更深。事实上，这种地震活动位于地壳内的“冷”俯冲带，如阿拉斯加和东北，而在地幔中的“温暖”俯冲带，如卡斯卡迪亚和南开，这表明流体发挥了重要作用。将评估地震波传播速度的方向依赖性，以便解释地震位置可能存在的偏差。与此同时，还将获得有关粘滞流动地幔内部变形的信息。横波速度和纵波速度的比值将表明流体是否存在。这些限制将指导俯冲带地幔流动和温度的计算机模拟。这些结果将与板块脱水导致的矿物相变的岩石学模型相联系，这些模型在板块界面附近引入流体，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的相互作用。与日本科学家的国际合作提供了获得最好的仪器和充分研究的日本俯冲系统的机会。这项研究利用了在卡斯卡迪亚的NSF GeoPRISMS和EarthScope计划中正在进行的工作，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.