Observations of Fault Growth Under Elevated Fluid Pressure Using Dynamic Microtomography

像圣安德烈亚斯断层这样的构造断层的突然运动引起地震。更好的地震风险评估需要断层分布和传播的定量知识。慢滑事件的发现，那些发生在几个小时到几个月而不是几秒钟的事件，发生在板块交界处，比如太平洋西北部，为研究地震和其他断层不稳定性的机制提供了新的机会。地震观测将慢滑事件与断裂带内的高流体压力联系起来，但这在机械上是如何起作用的尚不清楚。最近在实验室模拟这些条件的研究表明，孔隙压力的增加减缓了断层的生长。该项目旨在推进这些实验，以提高我们对高孔隙压力下缓慢断裂机制的理解。这项工作对我们对海岸板块边界以及其他看到这种复杂断层的地区的地震危险性的理解有更广泛的影响。研究人员还将为大学生提供研究经验，并在附近的高中开展外联活动，让学生进入科学实验室。该项目资助博士后1名，研究生1名。研究人员推测，裂纹尖端的膨胀硬化会导致变形迁移，从而导致断裂的非局部化和缓慢的断层扩展。为了验证这一假设，本研究利用x射线透明变形装置进行变形实验，实时记录断层的生长情况。最先进的动态微层析成像技术将阐明变形岩石在原位条件下的断层成核过程和生长模式。他们还将在损伤模型中加入剪胀硬化来模拟孔隙压力对断层扩展的影响。数值模拟生成的三维微观结构与延时断层扫描图像的比较将为变形机制提供新的见解。目标是更好地理解断层缓慢生长的机制，从而在地震周期的震间期提供地球物理观测与大型逆冲断层应力状态之间的关键联系。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。

Sudden motions of a tectonic fault such as the San Andreas fault cause earthquakes. Better seismic risk assessment requires quantitative knowledge of fault distribution and propagation. The discovery of slow slip events, those that occur over hours to months instead of seconds, at convergent plate boundaries, like in the Pacific Northwest, provides new opportunities to study the mechanics of earthquakes and other fault instabilities. Seismic observations link slow slip events to high fluid pressure within the fault zones but how this works mechanically is still unclear. Recent studies in the lab that emulate these conditions show that increasing pore pressure slow down fault growth. This project looks to advance these experiments to improve our understanding of the mechanics of slow faulting under high pore pressure. The work has broader impacts on our understanding of seismic hazards at coastal plate boundaries as well as other areas that see this type of complex faulting. The researcher will also provide a research experience for an undergraduate, and conduct outreach to a nearby high school to bring students into a scientific lab. The project supports a postdoctoral fellow and a graduate student.The researchers hypothesize that dilatant hardening at crack tip can cause deformation to migrate, which results in delocalized fracturing and slow fault propagation. To test this hypothesis, the work enables deformation experiments using an X-ray transparent deformation apparatus to record the real-time fault growth. The state-of-the-art dynamic microtomography imaging will elucidate the fault nucleation process and growth pattern in a deforming rock at in-situ conditions. They will also incorporate dilatancy hardening into the damage model to simulate the effect of pore pressure on fault propagation. Comparison of the 3-D microstructure generated by numerical simulations and the time-lapse tomography images will provide new insights into deformation mechanisms. The goal is to build a better understanding of the mechanics of slow fault growth, and thus provide the critical link between the geophysical observations and the stress states of a megathrust fault during the interseismic period of an earthquake cycle.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.