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

地垒和地堑俯冲对日本海沟沉积物通量和浅层滑脱几何形状的影响

• 批准号: 2103514
• 负责人: Christine Regalla
• 金额: $ 31.83万
• 依托单位: Northern Arizona University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-06-15 至 2025-05-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2103514&HistoricalAwards=false
• 关键词: Impact; horst; graben; subduction; sediment

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.

俯冲带是两个构造板块汇合的地方，会产生世界上最大的地震和海啸，并对沿海社区构成重大危险。虽然人们普遍了解这些类型的事件可能发生在哪里，但人们对决定它们何时发生以及最大震级将是什么的地质过程知之甚少。日本东北边缘(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，是评估板块界面和围岩地质性质的理想地点，这些板块界面和围岩承载着大地震和海啸。2011年地震和海啸的震级比灾害模型中预测的要大得多，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了强烈的地面震动和海水移动，从而产生了大海啸。这一事件突出表明，对控制俯冲带浅层孕震滑动的物理过程的认识存在重大差距。在这个项目中，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成分。将对进入的板块上的地垒地形在决定板块界面和围岩的几何和物理性质方面所起的作用进行评估。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海啸潜力。这样的框架不仅可以帮助改进日本的地震危险性和风险评估模型，而且还可以改进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、智利和中美洲俯冲区的部分地区。该项目将为博士生和本科生提供教育、培训和网络机会，这些学生将参与数据分析以及教育和外展计划。此外，还将开发一套幻灯片，介绍海洋地质学和地球物理学方面的各种地球科学家，供本科生、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，将放大未被充分代表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。Décolement几何结构、成分和输入沉积物上的通量是控制浅层巨型逆冲机制和俯冲带长期质量平衡的基本参数。尽管地垒和地堑的俯冲是常见的，但对于正常的断层俯冲如何影响板块边界界面和围岩的几何、力学和结构演化，以及控制浅层发震和海啸滑动的可能性的参数，几乎没有直接的约束。将测试进入的板块起伏如何影响浅层解冻的几何形状，以及在日本海沟已知存在浅层孕震滑移的部分中，吸积物质与构造侵蚀物质的相对体积和组成。对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，输入板块起伏是外部上升断层投掷和输入板块沉积物厚度的函数，通过控制物质被吸积、俯冲或构造侵蚀的位置，是控制消融的几何和组成的根本重要参数。有人提出，当下部板块起伏低于阈值时，有利于跨越地垒和地块的沉积和沉积，只有当起伏高于阈值时，才会形成平滑海底地形的构造侵蚀和平面沉积。这一想法将在日本海沟中得到检验，方法是将高分辨率水深测量和地震反射数据的海底构造地貌和构造图结合起来，以测量即将到来的地形起伏，量化上板块对沿剥离变形的响应，绘制出在额棱镜中发生叠置、伸展和坍塌的位置，并评估浅剥离的几何形状。该项目将制作一个浅层崩塌和正面棱镜的地下结构模型，以及一张经历沉积物吸积与构造侵蚀的区域地图，当与日本海沟的已知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、浅层崩塌几何形状和浅层滑动模式的影响。这项研究的结果适用于理解其他边缘地区，如阿拉斯加、汤加、智利和中美洲，具有较薄的来水沉积和地垒和地块地形的地震孕育潜力。此外，还将开发一套幻灯片，介绍海洋地质学和地球物理学方面的各种地球科学家，供本科生、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，将放大代表不足的群体中地球科学家的工作，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，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。