Impact of horst and graben subduction on sediment flux and shallow décollement geometry in the Japan Trench

俯冲带是两个构造板块交汇的地方，会产生世界上最大的地震和海啸，对沿海社区构成重大危害。 虽然人们普遍理解这些类型的事件可能发生在哪里，但对决定它们何时发生的地质过程以及它们的最大震级知之甚少。 2011年发生了9.1级大地震和海啸的日本东北部边缘（日本海沟的东北边缘）是评估发生大地震和海啸的板块界面和周围岩石的地质性质的理想地点。2011年地震和海啸的震级比灾害模型预测的要大得多，部分原因是断层破裂在板块边界的浅层产生了前所未有的大位移（高达50- 60米）。这种大的浅层滑动直接导致了强烈的地面震动和海水位移，产生了大海啸。 这一事件突出表明，在理解控制俯冲带浅层地震滑动的物理过程方面存在重大差距。在该项目中，日本海洋科学技术厅最近收集的新的高分辨率海底以下地球物理成像和海底测深数据将用于评估日本海沟板块界面浅层发生大地震的岩石的几何形状和组成。 地垒和地堑地形的作用，传入板块上的支配的几何形状和物理性质的板块界面和周围的岩石将进行评估。 这项工作的结果将有助于建立一个理论框架，了解海底地形，断层几何形状和断层岩石成分如何影响俯冲系统的地震和海啸潜力。这样的框架不仅可以帮助改善日本的地震灾害和风险评估模型，还可以帮助改善其他类似边缘地区的地震灾害和风险评估模型，例如阿拉斯加西部、卡斯卡迪亚北部、智利和中美洲俯冲带的部分地区。该项目将支持教育，培训和网络机会，为博士生和本科生谁将参与数据分析，并在教育和推广活动。此外，还将制作一套幻灯片，介绍海洋地质学和海洋物理学方面的各种地球科学家，供本科专业和普通教育课堂使用。 这些幻灯片将提供课程主题如何应用于真实的世界问题的例子，将放大代表性不足的群体中的地球科学家的工作，并将提供与学生可能认同的不同科学家的接触。沉降几何形状，成分和输入沉积物的通量是控制浅层巨型逆冲断层力学和俯冲带长期质量平衡的基本参数。虽然地垒和地堑的俯冲是常见的，但正断层俯冲如何影响板块边界界面和周围围岩的几何形状、力学和结构演化，以及控制浅层地震和海啸滑动潜力的参数，几乎没有直接的限制。 即将到来的板块浮雕如何影响的几何形状的浅的沉降和相对体积和组成的增生与构造侵蚀的材料在日本海沟的一部分，已知主机浅孕震滑动将进行测试。从日本海沟的高分辨率测深和多道地震数据的初步观察表明，传入的板块起伏，外隆断层落差和传入的板块沉积物厚度的函数，是一个根本的重要参数，通过控制物质的增生，俯冲，或构造侵蚀的几何形状和组成的沉降。 当下板块起伏度低于阈值时，沉积物增生和跨越地垒和地堑的沉降是有利的，而构造侵蚀和平坦海底地形的平面沉降只有在起伏度高于阈值时才形成。这一想法将在日本海沟得到检验，方法是综合利用高分辨率测深和地震反射数据绘制海底构造地貌和结构图，以测量入射的海底地形起伏，量化上板块对沿着滑脱变形的反应，绘制前棱柱中发生叠瓦、延伸和塌陷的位置，并评价浅层滑脱的几何形状。 该项目将制作一个浅层滑脱和前缘棱柱的地下结构模型，以及一幅经历沉积物堆积与构造侵蚀的区域图，与日本海沟已知的地震和古地震历史相比，可用于评估传入板块起伏对沉积物通量、浅层滑脱几何形状和浅层滑动模式的影响。 这项研究的结果是适用于了解地震的潜在的其他边缘薄传入沉积物和地垒和地堑地形，如阿拉斯加，汤加，智利和中美洲。此外，还将制作一套幻灯片，介绍海洋地质学和海洋物理学方面的各种地球科学家，供本科专业和普通教育课堂使用。 这些幻灯片将提供课程主题如何应用于真实的世界问题的例子，将放大代表性不足的群体中的地球科学家的工作，并将提供与学生可能认同的不同科学家的接触。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估来支持。

Subduction zones, where two tectonic plates converge, generate the world’s largest earthquakes and tsunamis, and present significant hazards to coastal communities. While it is generally understood where these types of events can occur, little is known about the geologic processes that dictate when they will occur and what their maximum magnitude will be. The Northeastern Japan margin (the Tohoku margin of the Japan Trench), which experienced a devastating M 9.1 earthquake and tsunami in 2011, is an ideal location to evaluate the geologic properties of the plate interface and surrounding rocks that host large earthquakes and tsunamis. The magnitudes of the 2011 earthquake and tsunami were much larger than had been predicted in hazard models, in part because the fault rupture produced an unprecedented large displacement (up to 50-60m) in the shallow part of the plate boundary. This large shallow slip directly led to intense ground shaking and seawater displacement that produced the large tsunami. This event highlighted significant gaps in the understanding of the physical processes that control shallow seismogenic slip in subduction zones. In this project, new high-resolution sub-seafloor geophysical imaging and seafloor bathymetry data, recently collected by the Japan Agency for Marine Science and Technology, will be used to evaluate the geometry and composition of the rocks that host large earthquakes in the shallow portion of the plate interface in the Japan trench. The role that horst-and-graben-topography on the incoming plate has on dictating the geometry and physical properties of the plate interface and surrounding rocks will be evaluated. Results from this work will help build a theoretical framework for understanding how seafloor topography, fault geometry, and fault rock composition impact the seismogenic and tsunamigenic potential of subduction systems. Such a framework can help improve seismic hazard and risk assessment models not only in Japan, but also in other analogous margins, such as portions of the western Alaska, north Cascadia, Chilean, and Central American subduction zones. This project will support education, training, and networking opportunities for a PhD student and undergraduate student who will participate in data analysis and in an education and outreach initiatives. In addition, a slide set featuring a diverse range of geoscientists in marine geology and geophysics will be developed to use in undergraduate major and general-education classrooms. These slides will provide examples of how course topics apply to real world problems, will amplify the work of geoscientists in underrepresented groups, and will provide exposure to a diverse set of scientists with whom students may identify.Décollement geometry, composition, and the fluxes on input sediments are fundamental parameters that control shallow megathrust mechanics and the long-term mass balances at subduction zones. Although the subduction of horst and graben is common, there exist few direct constraints on how normal fault subduction affects the geometry, mechanics, and structural evolution of the plate boundary interface and surrounding wall rock, parameters proposed to control the potential for shallow seismogenic and tsunamigenic slip. How incoming plate relief affects the geometry of the shallow décollement and the relative volumes and composition of accreted versus tectonically eroded material in a portion of the Japan trench known to host shallow seismogenic slip will be tested. Preliminary observations from high-resolution bathymetric and multichannel seismic data in the Japan trench suggest incoming plate relief, a function of outer rise fault throw and incoming plate sediment thickness, is a fundamentally important parameter governing the geometry and composition of the décollement by controlling where material is accreted, subducted, or tectonically eroded. It is proposed that sediment accretion and décollements that step over horst and graben are favored when lower plate relief is below a threshold value, and that tectonic erosion and planar décollements that smooth seafloor topography only form when relief is above a threshold. This idea will be tested in the Japan trench by integrating submarine tectono-geomorphic and structural mapping of high-resolution bathymetry and seismic reflection data to measure incoming pate relief, to quantify the upper plate response to deformation along the décollement, to map where imbrication, extension, and slumping occur in the frontal prism, and to evaluate the geometry of the shallow décollement. This project will produce a subsurface structural model of the shallow décollement and frontal prism and a map of regions experiencing sediment accretion versus tectonic erosion that, when compared to the known seismic and paleoseismic history of the Japan trench, can be used to evaluate the impact of incoming plate relief on sediment fluxes, shallow décollement geometry, and the mode of shallow slip. Results from this study are applicable for understanding the seismogenic potential of other margins with thin incoming sediments and horst and graben topography, such as Alsaska, Tonga, Chile, and Central America. In addition, a slide set featuring a diverse range of geoscientists in marine geology and geophysics will be developed to use in undergraduate major and general-education classrooms. These slides will provide examples of how course topics apply to real world problems, will amplify the work of geoscientists in underrepresented groups, and will provide exposure to a diverse set of scientists with whom students may identify.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.