Collaborative Research: Evaluating the contribution of crustal deformation to the present-day tectonics of convergent margins: the southern Cascadia forearc

俯冲带是地球上最大最具破坏性地震的发生地。在两次地震之间，地壳会积累应变，这可以通过贴在地面上的GPS标记逐渐移动（大地测量观测）来观察到。此外，地壳在数百万年的更长时间尺度上变形，比如山脉的隆起。大地测量观测和长期形变之间的关系还没有得到很好的理解，特别是在俯冲带的地震灾害方面。这个问题在卡斯卡迪亚俯冲带的南端尤其具有挑战性，在加利福尼亚北部和俄勒冈南部的近海，地壳受到俯冲和从圣安德烈亚斯断层系统向南转移的构造板块运动的影响。然而，南卡斯卡迪亚的地质特征使该地区非常适合理解和隔离可能导致上部地壳变形和地震的过程。这些特征包括高地形、高抬升率和高侵蚀率；适合测定年代的岩石和沉积物；还有三种潜在的、可测试的过程，可以产生地壳变形和俯冲带地震。这项研究的目的是更好地了解俯冲带是如何工作的，并预测未来地震的大小和时间。除了研究目标之外，该项目还包括与Hoopa Valley小学的教师合作，为六年级学生开发地球科学领域和实验室练习。Hoopa小学位于科学中心地区的中心，主要服务于美国印第安学生。虎霸小学的老师们将加入研究团队，进行暑期实地考察。该项目的大学教师和学生将与教师一起开展实践活动和实地考察，使六年级学生能够使用实际数据-这项研究的结果-实践科学研究的每一步。该研究项目还将促进其他预期的社会成果，如妇女和代表性不足的少数民族充分参与STEM，以及通过对研究生和本科生的培训和对早期职业研究人员的支持，培养多元化的、具有全球竞争力的STEM劳动力。北美卡斯卡迪亚板块边界的南端标志着卡斯卡迪亚岩石圈俯冲向圣安德烈亚斯转换断裂的转变。这个复杂的变形区域，门多西诺三重交界处，在空间和时间上都是迁移的。局部的岩石隆升和侵蚀速率、阶地形成和河道形态都与门多西诺三联结（Mendocino Triple Junction）和可能的布兰科断裂带（Blanco Fracture Zone）的北移有关。布兰科断裂带是胡安·德·富卡板块与其戈达板块之间的地理边界。由于对卡斯卡迪亚前弧上板块的长期变形及其构造驱动因素的了解有限，因此很难在观测到的现今变形模式中分离出地震周期信号。特别是来自不同地质信号的叠印——俯冲板块特征的迁移差异和与门多西诺三联结相关的地壳增厚传播波——需要在一系列时间尺度上对变形和地形变化进行评估。本项目是对南卡斯卡迪亚晚新生代隆升、挖掘和侵蚀的综合研究。通过使用多种对不同速率和时间过程敏感的地质年代学指标（即：AHe热年代学[岩石挖掘1Ma]，宇宙成因放射性核素埋藏定年[抬升速率限制在~0-5Ma]，以及宇宙成因放射性核素衍生的盆地平均侵蚀速率[过去~100ka的平均值]），这将有可能发展出挖掘和侵蚀的时间记录，并探测到南部前弧的空间变化。残存景观遗迹的保存将用于重建长波变形/隆起模式，并量化晚新生代的地形起伏。最后，利用地球动力学模型探索上板块永久变形的驱动机制，并探讨南卡斯卡迪亚构造变形如何影响观测大地测量数据记录的信号。这项研究将通过隔离和识别（可恢复的）地震周期变形和构造驱动的贡献，帮助估计俯冲带的地震危害，地质时间尺度的变形非常适合记录正在进行的构造变形和相关应变。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 are the sites of the Earth's largest and most damaging earthquakes. Between earthquakes, the Earth's crust accumulates strain, which is observed in gradual movement of GPS markers affixed to the ground (geodetic observations). In addition, the Earth's crust deforms over longer timescales of millions of years, such as the uplift of mountain ranges. The relationship between geodetic observations and long-term deformation is not well understood, especially with respect to earthquake hazards in subduction zones. This problem is particularly challenging at the southern end of the Cascadia Subduction zone, offshore of northern California and southern Oregon, where the Earth's crust is influenced both by subduction and by tectonic plate motion transferred from the San Andreas fault system to the south. However, the geologic characteristics of southern Cascadia make this region well-suited for understanding and isolating the processes that could drive upper crustal deformation and earthquakes. These characteristics include a combination of high topography, high uplift rates, and high erosion rates; rocks and deposits suitable for dating; and three potential, and testable, processes that could generate crustal deformation and subduction zone earthquakes. The goal of this research is to better understand how subduction zones work and to anticipate the size and timing of future earthquakes. In addition to the research objectives, this project includes partnering with faculty at Hoopa Valley Elementary School to develop geoscience field and laboratory exercises for sixth grade students. Hoopa Elementary is located in the heart of the region of scientific focus and serves primarily American Indian students. Hoopa Elementary School teachers will join the research team for summer field work. The project's university faculty and students will join the teachers in developing hands-on activities and field trips that will enable sixth grade students to practice each step of scientific research using real data - the results from this research. The research project would also advance other desired societal outcomes such as full participation of women and underrepresented minorities in STEM and development of a diverse, globally competitive STEM workforce through graduate and undergraduate student training and support of an early career researcher.The southern end of the Cascadia plate boundary in North America is marked by transition from Cascadia lithospheric subduction to San Andreas transform faulting. This complex region of deformation, the Mendocino Triple Junction, is migratory in space and time. Localized rock uplift and erosion rates, terrace formation, and river channel morphology have responded to northward movement of the Mendocino Triple Junction and possibly the Blanco Fracture Zone, which is a physiographic boundary between the Juan de Fuca plate and its Gorda segment. Limited understanding of the long-term deformation in the upper-plate of the Cascadia forearc and its tectonic drivers make it difficult to isolate the earthquake-cycle signal within observed patterns of present-day deformation. In particular, overprinting from different geologic signals - migratory differences in the character of the subducting plate and the propagating wave of crustal thickening associated with the Mendocino Triple Junction - requires an evaluation of deformation and topographic change across a range of timescales. This project is an integrated study of the Late Cenozoic uplift, exhumation and erosion of Southern Cascadia. By using multiple geochronologic proxies that are sensitive to different rates and timings of processes (i.e., AHe thermochronology [rock exhumation 1Ma], cosmogenic radionuclide burial dating on buried surfaces that are presently uplifted [uplift rate constrained from ~0-5Ma], and cosmogenic radionuclide-derived basin averaged erosion rates [averaged over last ~100ka]), it will be possible to develop a record of exhumation and erosion through time and detect spatial variations in the southern forearc. The preservation of relict landscape remnants will be exploited to reconstruct long-wavelength deformation/uplift patterns and to quantify relief production in the Late Cenozoic. Finally, geodynamic models will be used to explore the mechanisms driving permanent upper plate deformation, and address how tectonic deformation of southern Cascadia may impact the signal recorded in observed geodetic data. This research will aid estimation of earthquake hazards at subduction zones by isolating and identifying the contribution of (recoverable) earthquake cycle deformation and of tectonically-driven, geologic time scale deformation at a site well suited to record ongoing tectonic deformation and associated strain.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.