Collaborative Research: Heterogeneous Rupture of Great Cascadia Earthquakes Inferred from Coastal Subsidence Estimates

合作研究：从海岸沉降估计推断卡斯卡迪亚大地震的非均质破裂

• 批准号: 1419824
• 负责人: Benjamin Horton
• 金额: $ 12.95万
• 依托单位: Rutgers University New Brunswick
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-09-01 至 2019-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1419824&HistoricalAwards=false
• 关键词: Collaborative; Research; Heterogeneous; Rupture; Great

Of the major subduction zones worldwide, Cascadia has not experienced rupture in the historical period. For example, each of the Alaska, Chile, Sumatra, Kamchatka, and Japan/Kurils subduction zones experienced multiple megathrust ruptures greater than magnitude 8.5 during this time. A critical step toward understanding Cascadia?s rupture patterns is reconstructing its land-level history over the past few thousands of years, a history that is linked to past earthquake cycles. This project uses a novel statistically-based microfossil (foraminifera and diatoms) analysis coupled with computer modeling to quantify coseismic subsidence in Cascadia tidal sediments to determine the rupture patterns of the Cascadia subduction. This project will produce data that is important to the assessment of seismic and tsunami hazards along the Pacific coast of North America, as well as for sites subject to teleseismic tsunamis produced by this region. The project has high potential to benefit society or advance desired societal outcomes through: 1) full participation of women in STEM; 2) increased public scientific literacy and public engagement with science and technology through public outreach efforts; 3) improved well-being of individuals in society through a better understanding of earthquake hazards in Cascadia coupled with planned outreach resource managers, decision makers, planners; 4) development of a diverse, globally competitive STEM workforce through development of early career researchers, mentoring of a post-doctoral scholar, involvement of graduate and undergraduate students in research, and activities for high school and community college students.Wetland sediments fringing estuaries at the Cascadia subduction zone harbor a record of plate-boundary earthquakes during the past 5,000 years. These are inferred from stratigraphic evidence of interbedded peaty and muddy sediment beneath tidal wetlands that are used to reconstruct land-level changes. However, the precision of past measurements of land-level changes at Cascadia is low and the measurements are spatially limited. This makes past measurements insufficient for determining which hypotheses of plate-boundary deformation are most valid. This project will re-dress this deficiency by applying recently developed statistical transfer functions to microfossils to reconstruct Cascadia's rupture patterns and timing and magnitude of strain release over several thousands of years. This technique will be employed to test three hypotheses regarding the nature of rupture during the AD 1700 and three earlier megathrust earthquakes: 1) Coseismic subsidence varied spatially and temporally during past Cascadia plate-boundary earthquakes; 2) Estimates of coseismic subsidence can differentiate between wide and narrow rupture widths; and 3) More precise dating of earthquake evidence allows more direct evaluation of megathrust segmentation. Field, laboratory, computational, and theoretical investigations will focus on four earthquake events from six estuaries from southern Oregon to northern Washington. These carefully selected sites also include a strike-normal transect. A combined approach of stratigraphic description of buried soils, AMS 14C dating and multi-proxy microfossil transfer functions, supported by testate amoebae and geochemistry, will result in the construction of land-level changes. A 3D dislocation model with the 3D megathrust fault geometry will be used to compare coseismic deformation to with paleoseismic estimates.

在全球主要俯冲带中，卡斯卡迪亚在历史时期没有经历过断裂。例如，阿拉斯加、智利、苏门答腊岛、堪察加半岛和日本/千岛群岛俯冲带在此期间都经历了多次大于 8.5 级的巨型逆冲断裂。了解卡斯卡迪亚破裂模式的关键一步是重建其过去几千年的陆地历史，这段历史与过去的地震周期有关。该项目使用一种新颖的基于统计的微化石（有孔虫和硅藻）分析结合计算机建模来量化卡斯卡迪亚潮汐沉积物中的同震沉降，以确定卡斯卡迪亚俯冲的破裂模式。该项目将产生的数据对于评估北美太平洋沿岸的地震和海啸灾害以及该地区发生远震海啸的地点非常重要。该项目通过以下方式具有造福社会或推进预期社会成果的巨大潜力：1）妇女充分参与 STEM； 2) 通过公共宣传工作提高公众科学素养和公众对科学技术的参与； 3) 通过更好地了解卡斯卡迪亚的地震灾害以及有计划的外展资源管理者、决策者、规划者，改善社会个人的福祉； 4) 通过培养早期职业研究人员、指导博士后学者、让研究生和本科生参与研究以及为高中生和社区学院学生开展活动，培养多元化、具有全球竞争力的 STEM 劳动力队伍。卡斯卡迪亚俯冲带河口边缘的湿地沉积物保​​存着过去 5,000 年来板块边界地震的记录。这些是根据潮汐湿地下方泥炭和泥质沉积物互层的地层证据推断出来的，这些沉积物用于重建土地平面变化。然而，过去对卡斯卡迪亚陆地平面变化的测量精度较低，而且测量空间有限。这使得过去的测量不足以确定哪些板块边界变形的假设最有效。该项目将通过将最近开发的统计传递函数应用于微化石来弥补这一缺陷，以重建卡斯卡迪亚的破裂模式以及数千年来应变释放的时间和幅度。该技术将用于检验关于公元 1700 年和三场早期大型逆冲地震期间破裂性质的三个假设：1）过去卡斯卡迪亚板块边界地震期间同震沉降在空间和时间上发生变化； 2）同震沉降的估计可以区分宽破裂宽度和窄破裂宽度； 3）更精确的地震证据年代测定可以更直接地评估巨型逆冲断层分段。现场、实验室、计算和理论研究将集中于从俄勒冈州南部到华盛顿州北部六个河口的四次地震事件。这些精心挑选的地点还包括一条走向正常的横断面。埋藏土壤地层描述、AMS 14C 测年和多代理微化石传递函数的综合方法，在有遗嘱变形虫和地球化学的支持下，将导致陆地水平变化的构建。具有 3D 巨型逆冲断层几何结构的 3D 位错模型将用于将同震变形与古地震估计进行比较。