Collaborative Research: Characterizing Quaternary Fault Behavior and Surface Processes of an Active Rift: The Lake Malawi (Nyasa) Rift, East Africa

合作研究：表征第四纪断层行为和活动裂谷的表面过程：东非马拉维湖（尼亚萨）裂谷

• 批准号: 2116017
• 负责人: Christopher Scholz
• 金额: $ 76.38万
• 依托单位: Syracuse University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-04-01 至 2025-03-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2116017&HistoricalAwards=false
• 关键词: Collaborative; Research; Characterizing; Quaternary; Fault

The earliest phases of the formation of ocean basins involve the break-up of the continents. The study of continental rifts is essential for understanding hazards and potential for natural resources. The process of rifting involves active faulting, volcanic activity and associated earthquakes, and are linked with significant hazards. Rifting also leads to the formation of basins that trap sediment and can host oil and gas deposits. A fundamental question in continental rift systems is how rifting is distributed across different fault systems and how surface processes, including changes in sediment supply, erosion and lake levels may impact fault behavior. These early phase geological structures act as recorders of the different processes, but after many years of seafloor spreading, are usually buried beneath thick packages of ocean sediment, and thus mature continental margins, and ocean basins, are difficult places to study early-rifting processes. On the other hand, active continental rifts, where continents are in the early stages of break-up, reveal exposed and/or shallow geological structures and deposits related to rifting. This study considers a part of the East African Rift Valley that is nearly fully flooded with freshwater (the Lake Malawi Rift), where very high quality and relatively low cost marine geophysical methods can be used to image the floor of the rift and its subsurface. By collecting very high resolution geophysical images and integrating with information from previous academic drilling and with numerical modeling, we will reconstruct fault geometries and slip rates over the last hundreds of thousands of years, evaluate controls on why particular faults are active, and estimate past earthquake activity. Results of the study will allow for a better understanding of how rift faults may be preserved and how they can be reactivated on passive continental margins, for instance on the East Coast of North America that was formed by the rifting of North America from Africa. In addition, this study will also provide information on how rift faults redirect flows of sediment into a rift valley and assist in understanding oil and gas occurrences in rift systems as well as the role of climate-driven surface processes that may influence faulting and earthquake activity. We will train 3 doctoral students and a post-doctoral scholar during the project. Our international team consists of both U.S. residents and East African nationals, including two of the latter matriculated at Syracuse University, and we anticipate roughly equal representation by female and male researchers on the field team. We will execute an extensive outreach program in Malawi, both at institutions of Higher Education and in secondary schools, and develop museum displays in Malawi. We will interact deeply with our Malawian scientific colleagues, and also engage with the Malawi Departments of Fisheries and Antiquities to share new data sets to key stakeholders.We will undertake a combined observational, analytical and numerical modeling study of Quaternary deformation and surface processes associated with a series of active fault zones in the active Lake Malawi Rift, in the western branch of the East African Rift System. This system is one of the largest active rifts in the world and is emblematic of an early-phase, low strain rate rift in a weakly magmatic system. We will use robust marine-type high-resolution seismic and echosounder tools to make high-fidelity observations across several different structural settings. Using new offshore observations from multibeam echosounder data and high-resolution CHIRP seismic reflection data, we will determine how recent (last 25-100 ka) deformation on intrarift faults is distributed across the rift and assess how intrarift faults have propagated along their length and then linked together over time. We will generate time-displacement profiles across a series of fault zones in different structural settings (e.g., flexural vs. border fault margin settings); generate a library of fault length-displacement relationships for the different fault systems; and use classical scaling laws to estimate records of past earthquakes over the past 100 ka. The fault displacement records will be chronologically constrained by the superbly-dated, high-resolution syn-rift stratigraphy from the Lake Malawi Drilling Program, extended from the drill cores into the new grids of CHIRP seismic reflection data. The new fault displacement histories will be compared to known high-resolution hydroclimate records to determine if changes in climate regimes modulate rift fault activity. Our numerical modeling efforts will assess the stress regimes associated with changes in water and sediment loading and erosion across the rift, which will be compared with observations. New lake floor bathymetric data will reveal how structurally-controlled sediment dispersal paths have developed in the Malawi Rift, leading to a better understanding basin-filling processes in rift-lake systems. Results from our study will provide unique new constraints on past earthquake histories and provide the basis for probabilistic seismic hazard assessments.Funding for this project is provided by NSF EAR Tectonics and Geophysics Programs.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.

海盆形成的最早阶段涉及大陆的破裂。 大陆裂谷的研究对于理解危害和自然资源的潜力至关重要。裂谷的过程涉及主动断层，火山活动和相关地震，并与重大危害有关。裂谷还导致形成捕获沉积物并可以容纳石油和天然气沉积物的盆地的形成。大陆裂谷系统中的一个基本问题是裂谷如何分布在不同的断层系统中，以及表面过程（包括沉积物供应，侵蚀和湖泊水平的变化）如何影响断层行为。这些早期的地质结构充当了不同过程的记录，但是经过多年的海底扩散，通常将其埋在厚厚的海洋沉积物包装下，从而成熟的大陆边缘和海盆是很难研究早期流程过程的地方。另一方面，大陆处于分裂的早期阶段的活跃大陆裂谷，揭示了与裂谷有关的暴露和/或浅层地质结构和沉积物。 这项研究考虑了东非裂谷的一部分，几乎完全充满了淡水（马拉维湖裂谷），那里可以使用非常高的质量和相对较低的海洋地球物理方法来对裂谷及其地下的地板进行成像。 通过收集非常高的分辨率地球物理图像并与以前的学术钻探和数值建模的信息相结合，我们将在过去数十万年内重建故障的几何形状和滑动速率，评估控制特定故障为什么活动的控制，并估算过去的地震活动。这项研究的结果将可以更好地了解如何保留裂谷的断层以及如何在被动大陆边缘重新激活它们，例如，在北美北美由北美裂口形成的北美东海岸。此外，这项研究还将提供有关裂谷断层如何重定向沉积物流动到裂谷谷的信息。 在该项目期间，我们将培训3名博士生和一名博士后学者。我们的国际团队由美国居民和东非国民组成，其中包括锡拉丘兹大学后的两个入学，我们预计女性和男性研究人员在现场团队中的代表大致相同。 我们将在马拉维执行广泛的外展计划，包括高等教育机构和中学机构，并在马拉维开发博物馆展览。 我们将与我们的马拉维科学同事进行深入互动，并与马拉维渔业和古物部门互动，以与关键利益相关者共享新的数据集。我们将进行一项合并的观察，分析和数值建模，与Quaternary变形和表面过程有关东非裂谷系统西部分支的马拉维湖裂谷中的一系列主动断层区域。 该系统是世界上最大的活跃裂痕之一，它是弱岩浆系统中早期低应变率裂痕的象征。我们将使用强大的海洋型高分辨率地震和回声器工具来对几种不同的结构环境进行高保真观察。 使用来自多层回声器数据和高分辨率CHIRP地震反射数据的新离岸观测值，我们将确定在整个裂痕上分布到较新的（最后25-100 ka）的变形（最后25-100 ka）在整个裂痕上分布并评估弹药内断层的沿其长度和长度延伸的方式随着时间的推移链接在一起。我们将在不同的结构设置中（例如，弯曲与边界故障边缘设置）中生成一系列故障区域的时间置换曲线；为不同的故障系统生成故障长度置换关系的库；并使用经典的缩放法则来估计过去100 ka的过去地震记录。 断层位移记录将在按时间顺序上受到马拉维湖钻探计划的卓越日期，高分辨率的同步地层学的约束，从钻芯扩展到Chirp Seismic Reflection数据的新网格。 新的断层位移历史将与已知的高分辨率氢化记录进行比较，以确定气候状态的变化是否调节裂谷断层活动。 我们的数值建模工作将评估与整个裂谷的水和沉积物负荷和侵蚀变化相关的应力制度，这将与观察结果进行比较。 新的湖泊地板测深数据将揭示马拉维裂谷中结构控制的沉积物分散路径，从而更好地了解Rift Lake Systems的盆地填充过程。 我们研究的结果将为过去的地震历史提供独特的新约束，并为概率地震危害评估提供了基础。该项目的资金由NSF EAR Tectonics和Geophysics Program提供。这项奖项反映了NSF的法定任务，并被视为值得支持的支持。通过使用基金会的智力优点和更广泛影响的评论标准进行评估。

项目成果

Climate-driven stress changes and normal fault behavior in the Lake Malawi (Nyasa) Rift, East Africa

东非马拉维湖（尼亚萨）裂谷气候驱动的应力变化和正常断层行为

• DOI: 10.1016/j.epsl.2022.117693
• 发表时间: 2022
• 期刊: Earth and Planetary Science Letters
• 影响因子: 5.3
• 作者: Xue, Liang;Moucha, Robert;Scholz, Christopher A.
• 通讯作者: Scholz, Christopher A.