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和最具破坏性的地震的发生地。在两次地震之间，地壳会累积应变，这在贴在地面上的GPS标记的逐渐移动(大地测量)中可以观察到。此外，地壳还会在数百万年的较长时间尺度上变形，例如山脉的隆起。大地测量和长期形变之间的关系还不是很清楚，特别是关于俯冲带的地震灾害。这个问题在卡斯卡迪亚俯冲带的南端，加利福尼亚州北部和俄勒冈州南部的近海尤其具有挑战性，那里的地壳既受到俯冲的影响，也受到从圣安德烈亚斯断裂系统向南转移的构造板块运动的影响。然而，卡斯卡迪亚南部的地质特征使该地区非常适合理解和隔离可能驱动地壳上部变形和地震的过程。这些特征包括高地形、高隆起率和高侵蚀率的组合；适合测年的岩石和沉积物；以及可能产生地壳变形和俯冲带地震的三个潜在的和可测试的过程。这项研究的目标是更好地了解俯冲带是如何工作的，并预测未来地震的规模和时间。除了研究目标，该项目还包括与霍帕谷小学的教职员工合作，为六年级学生开发地球科学领域和实验室练习。胡帕小学位于科学中心区的中心，主要为美国印第安人学生服务。胡帕小学的教师将加入研究团队，进行暑期实地考察。该项目的大学教职员工和学生将与教师一起开展动手活动和实地考察，使六年级的学生能够使用真实数据--这项研究的结果--练习科学研究的每一步。该研究项目还将推动其他预期的社会成果，例如妇女和代表性不足的少数民族充分参与STEM，并通过研究生和本科生培训以及对早期职业研究人员的支持，发展一支多样化的、具有全球竞争力的STEM劳动力队伍。北美卡斯卡迪亚板块边界的南端是从卡斯卡迪亚岩石圈俯冲到圣安德烈亚斯转换断层的过渡。这个复杂的形变区域，门多西诺三重结，在空间和时间上是迁移的。局部的岩石抬升和侵蚀速率、阶地形成和河道形态对门多西诺三重结合部以及可能的Blanco断裂带的北移做出了响应，Blanco断裂带是Juan de Fuca板块与其Gorda段之间的地形分界线。对卡斯卡迪亚前弧上板块的长期形变及其构造驱动因素的了解有限，使得很难将地震周期信号与观测到的现代形变模式分开。特别是，来自不同地质信号的叠印--俯冲板块性质的偏移差异和与门多西诺三重结合部有关的地壳增厚传播波--需要评估一系列时间尺度上的变形和地形变化。该项目是对卡斯卡迪亚南部晚新生代隆升、折返和侵蚀的综合研究。通过使用对不同过程的速率和时间敏感的多个地质年代学替代物(即热年代学[岩石折返1 Ma]、在目前隆起的埋藏面上的宇宙成因放射性核素埋藏测年[隆升速率约束在~0-5 Ma]和宇宙成因放射性核素衍生的盆地平均侵蚀速率[过去平均~100ka])，将有可能建立随时间的折返和侵蚀记录，并探测南部前弧的空间变化。遗迹景观的保护将被用来重建长波形变/隆起模式，并量化晚新生代的地貌生产。最后，地球动力学模型将被用来探索驱动永久上板块变形的机制，并解决卡斯卡迪亚南部的构造变形如何影响观测大地测量数据中记录的信号。这项研究将通过在适合记录持续构造变形和相关应变的地点隔离和识别(可恢复的)地震周期变形和构造驱动的地质时间尺度变形的贡献，帮助评估俯冲带的地震危险。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。

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.