CAREER: Experimental investigation of deformation and slip behaviors of subduction megathrust rocks

毁灭性的地震和海啸在俯冲带反复发生，大地震事件之间的时间间隔从几十年到几个世纪不等。长期的国际合作研究和教育计划对于增进对震源物理的了解并将过去事件的知识传递给子孙后代是必要的。为了促进对巨型逆冲板块边界断层的变形和滑动行为以及俯冲带地震物理的了解，该项目涉及在沿板块边界断层预期的高压和温度条件下对天然断层岩进行创新的变形和摩擦实验。为了扩大学生在实验岩石变形和俯冲带地震和海啸灾害方面的学习机会，首席调查员开发了新的教育计划，包括高级顶石课程、为地球科学和工程方面的研究生和职业生涯早期科学家提供的培训课程，以及将教育学生关于俯冲带地震和海啸以及自然灾害减灾的国际实地考察。这些教育项目旨在提供岩石变形方面的实践实验室经验，以及对俯冲带地震的见解。通过这些计划，下一代研究人员将接受培训，以促进在构造、地球动力学和工程问题上的跨学科和国际合作，并推动发现和减轻自然灾害的传授给子孙后代。许多地球物理和地质观测，包括低地震速度、增积棱镜楔体的高反射率锥角和脉体的形成，都推断出沿着巨型逆冲板块边界断层发展的高孔隙流体压力，从而导致断层强度低。该项目将检验这样一种假设，即低有效应力下的变形和滑动行为可能控制沿巨型逆冲板块边界断层观察到的一系列滑动事件和地震。对天然巨型逆冲断层岩进行了一系列真三轴压缩试验、常规三轴拉伸试验和控制孔压下的三轴摩擦试验。通过控制孔隙压力的大小和增压速率，可以在一定加载路径和加载速率范围内实现较低的有效压力。这一系列实验将记录孔压升高以及加载路径和速率对剪切、拉伸和混合拉伸-剪切断裂和摩擦行为形成的影响，从而提供与板块边界断层滑动相关的静脉形成的力学观点。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。

Devastating earthquakes and tsunamis recur in subduction zones, and the time interval between large earthquake events ranges from decades and centuries. Long-lasting international collaborative research and education programs are necessary to advance understanding of earthquake source physics and transfer the knowledge from the past events to future generations. To advance understanding of deformation and slip behaviors of megathrust plate boundary faults and physics of earthquakes in subduction zones, this project involves development of innovative deformation and friction experiments on natural fault rocks at elevated pressure and temperature conditions that are anticipated along the plate boundary faults. To expand students' learning opportunities on experimental rock deformation and subduction zone earthquake and tsunami hazards, the principal investigator develops new education programs including a senior capstone course, a training course for graduate students and early-career scientists in geoscience and engineering, and an international field trip that will educate students on subduction zone earthquakes and tsunamis and hazard mitigation for natural disasters. The education programs are designed to provide hands-on laboratory experience in rock deformation and insights into subduction zone earthquakes. Trough these programs, next-generation researchers will be trained to facilitate interdisciplinary and international collaborations on tectonic, geodynamic, and engineering problems and to advance the transfer of discovery and natural hazard mitigation to future generations. Development of elevated pore fluid pressure along the megathrust plate boundary faults and thus low strength of faults are inferred from many geophysical and geological observations including low seismic velocity, high reflectivity taper angle of the accretionary prism wedge, and vein formation. This project will test the hypothesis that deformation and slip behaviors at low effective stress may control a spectrum of slip events and earthquakes observed along the megathrust plate boundary faults. A series of true-triaxial compression tests, conventional triaxial extension tests, and triaxial friction experiments under controlled pore pressure will be conducted on natural megathrust fault rocks. Low effective pressure at a range of loading paths and rates will be achieved by controlling of magnitude and pressurization rates of pore pressure. The series of experiments will document the effects of elevated pore pressure and loading paths and rates on the formation of shear, extensional, and hybrid extension-shear fracture and frictional behaviors, and thus can provide mechanical perspectives on vein formation associated with slip along the plate boundary faults.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.