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

两个构造板块交汇的俯冲带会产生世界上最大的地震和海啸，并对沿海社区造成重大危害。虽然人们普遍了解这些类型的事件可能发生的地点，但人们对决定它们何时发生和最大震级的地质过程知之甚少。日本东北部边缘（日本海沟的东北边缘）在2011年经历了毁灭性的9.1级地震和海啸，是评估发生大地震和海啸的板块界面和周围岩石地质特性的理想地点。2011年地震和海啸的震级比危险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部产生了前所未有的大位移（高达50-60米）。这种巨大的浅层滑动直接导致强烈的地面震动和海水位移，从而产生了大海啸。这一事件突出了在对控制俯冲带浅层发震滑动的物理过程的认识上的重大空白。在这个项目中，日本海洋科学技术机构（Japan Agency for Marine Science and Technology）最近收集的新的高分辨率海底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部发生大地震的岩石的几何形状和组成。将评估进入板块的地堑地形对决定板块界面和围岩的几何和物理性质的作用。这项工作的结果将有助于建立一个理论框架，以了解海底地形、断层几何形状和断层岩石组成如何影响俯冲系统的孕震和生海啸潜力。这样的框架不仅可以帮助改善日本的地震危险性和风险评估模型，还可以帮助改善其他类似边缘地区的地震危险性和风险评估模型，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。该项目将为参与数据分析、教育和推广活动的博士生和本科生提供教育、培训和交流机会。此外，还将开发一套幻灯片，展示海洋地质学和地球物理学领域的各种地球科学家，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现实世界问题的例子，将在代表性不足的群体中扩大地球科学家的工作，并将提供学生可能认同的各种科学家的机会。沉积物的几何形状、组成和输入沉积物的通量是控制浅层大逆冲力学和俯冲带长期物质平衡的基本参数。虽然断层和地堑的俯冲是常见的，但对于正断层俯冲如何影响板块边界界面和周围围岩的几何、力学和构造演化，并没有什么直接的约束条件，这些参数被用来控制浅层发震和海啸滑动的可能性。进入的板块起伏如何影响浅层地层的几何形状，以及在日本海沟已知的承载浅层发震滑动的部分地区，沉积与构造侵蚀物质的相对体积和组成将被测试。日本海沟的高分辨率测深和多通道地震数据的初步观测表明，外来板块的起伏是外部隆起断层抛断和外来板块沉积物厚度的函数，它是通过控制物质在何处被增生、俯冲或构造侵蚀来控制区域的几何形状和组成的一个基本重要参数。认为当下板块起伏低于阈值时，有利于沉积增积和跨地堑和地堑的沉积沉积；而当起伏高于阈值时，有利于形成平滑海底地形的构造侵蚀和平面沉积。这个想法将在日本海沟进行测试，通过整合海底构造地貌和高分辨率测深和地震反射数据的结构测绘来测量传入的地形起伏，量化沿dsamicment的上部板块对变形的反应，绘制前棱镜中发生叠瓦片、延伸和塌陷的位置，并评估浅层dsamicment的几何形状。该项目将产生一个浅层dsamen和正面棱镜的地下结构模型，以及一个经历沉积物增生与构造侵蚀的区域图，当与日本海沟已知的地震和古地震历史相比较时，可以用来评估进入的板块起伏对沉积物通量、浅层dsamen几何形状和浅层滑动模式的影响。该研究结果可应用于了解其他具有薄沉积和地堑地形的边缘地区的发震潜力，如阿尔萨斯加、汤加、智利和中美洲。此外，还将开发一套幻灯片，展示海洋地质学和地球物理学领域的各种地球科学家，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现实世界问题的例子，将在代表性不足的群体中扩大地球科学家的工作，并将提供学生可能认同的各种科学家的机会。该奖项反映了美国国家科学基金会的法定使命，并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，被认为值得支持。

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.